British Journal of Psychology (1992), 83, 479-491
Printed in Great Britain
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0 1992 The British Psychological Society
Effects of mood manipulation and anxiety on performance of an emotional Stroop task Anne Richards* Department of Pgcbology, Birkbeck College, Universig of London, Malet Street, London WClE 7HX, UK
Christopher C. French, Wendy Johnson, Jennifer Naparstek and Jane Williams Goldsmitbs’ College, University of London In Study 1 subjects high and low in trait anxiety were asked to identify the colour of anxiety-related, anxiety-matched neutral, happiness-related and happinessmatched neutral words. There were two types of stimulus presentation : blocked trials, where stimuli were blocked with respect to their valence, and mixed trials, where stimuli were mixed with respect to their valence. Subjects high in trait anxiety took longer to identify the colour of anxiety-related compared to matched neutral words for blocked-trial presentation only. In Study 2 subjects were exposed to either a positive or a negative mood-manipulation followed by a mixed-trial Stroop task. The mood manipulation procedure was successful in producing predicted changes in self-reported state anxiety. Analyses showed that high-trait-anxiety subjects exhibited interference effects consistent with the induced mood. No such effects were observed for the low-trait-anxiety subjects.
It has now been established beyond reasonable doubt that there are differences in information processing by anxious compared to non-anxious individuals. Research has examined both clinical and normal populations. Bower’s (1981) model proposes that subjects high in anxiety should have perceptual sensitivity for threat-related information. This model proposes that each distinct emotion has an emotion node in semantic memory. Emotion nodes may be activated by a variety of stimuli including symbolic verbal cues and physiological cues. Activation spreads from these nodes, resulting in increased activation in associated nodes. This model predicts that emotion will enhance the salience of mood-congruent material, resulting in an increase in perceptual sensitivity for that material. The model also predicts that there should be mood-dependent retrieval. The evidence for this latter prediction has been equivocal (e.g. Bower & Mayer, 1985, 1989). However, there has been a great deal of support for the former prediction. Research has clearly indicated that high-anxiety subjects have a selective attentional bias for threatening information (for reviews see Eysenck, MacLeod & Mathews, 1987; MacLeod, 1990; Williams, Watts, MacLeod & Mathews, 1988). Several studies have used a modified version of the Stroop paradigm (Stroop, * Requests for reprints.
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1935) to examine cognitive processes in anxiety. The classic paradigm involves presenting a subject with colour words written in different coloured inks. The subject’s task is to identify the colour of the ink whilst ignoring the semantic content of the word. When the colour of the ink is congruent with the word (e.g. ‘blue’ written in blue ink), the time taken to name the colour of the word is reduced compared to identifying the colour of a row of Xs. Conversely, on incongruent trials (e.g. ‘red’ written in blue ink), colours are named more slowly than for a row of Xs. The modified paradigm involves the presentation of emotional and non-emotional words in different coloured inks, and the task of the subject is to identify their colour. For example, an emotional word such as ‘mutilate ’ may be presented in say, red, and the task of the subject is to say ‘red’. Bower’s (1981) prediction of mood-congruent interference effects using the Stroop paradigm has generally been supported. Ray (1979) found that pre-examination students took longer to name the colour of examination-related Stroop words compared to matched-neutral words. Mood congruent interference effects were demonstrated by Mathews & MacLeod (1985) using clinically anxious patients, and by Williams & Broadbent (1986) with a sample of overdose patients, and by Watts, McKenna, Sharrock & Trezise (1986) with spider-phobics. All the above studies have presented Stroop words on cards. The subjects begin at the top left corner and speak out loud the colour names of the words. The cards contain words of all the same hedonic tone, that is, the cards consist entirely of threatening words or entirely of neutral words. Richards & Millwood (1989) departed from the standard paradigm in several ways. Firstly, a computer was used to present stimuli. Secondly, a manual as opposed to the more usual vocal response was required, and thirdly, words were presented individually on the screen. In the typical emotional Stroop paradigm response latencies reflect the time taken to identify a series of colour-words, including those trials on which errors were made. The computerized version differentiates between correct and incorrect responses. Richards & Millwood (1989) found that whereas low-trait-anxious subjects were unaffected by the hedonic tone of the stimulus words, high-trait-anxious subjects took longest to identify the colour of threat-related material and were quickest at identifying the colour of pleasant words. This study used trials mixed with respect to their valence. That is, each word could have been either threat-related, pleasant or neutral, and subjects could not predict the valence on a trial-to-trial basis. Richards & French (1990) used the computerized emotional Stroop paradigm with blocked presentation and found that high-trait-anxious subjects took longer to identify the colour of anxiety-related compared to matched neutral words. The present study directly compares the effects of presenting stimuli randomly mixed with respect to their valence with presenting stimuli blocked with respect to their valence. Neely (1976, 1977) and Stanovich & West (1979, 1981) put forward a two-process model of word recognition in which the first stage of lexical access is viewed as a process of automatic spreading activation. This is then followed by a second, optional, stage whereby there is a strategic allocation of limited capacity resources. The spreading activation effect appears very rapidly, reaching asymptotic levels in about 200 ms (Meyer & Schvaneveldt, 1971; Ratcliff & McKoon, 1981).
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If the interference effect for threat-related Stroop words is due to short-term automatic spreading activation we would expect comparable interference effects for both mixed-list and blocked presentation for high-trait subjects. This is because interference effects should occur on a trial-to-trial basis and dissipate prior to the onset of the next trial. On the other hand, if there are longer-lasting effects such as a mood manipulating effect of the words themselves, then we might expect there to be greater interference for blocked presentation compared to mixed-list presentation. Mood may build up across a block of emotional words but be unaffected by a block of neutral words. For example, high-trait-anxiety subjects may take longer to identify the colour of anxietyrelated words when they are presented under blocked conditions because the mood manipulating effect of the words themselves has an interfering effect. Thus, the interference effect for blocked presentation, as measured by the difference in reaction time to the anxiety-related block compared to the neutral block, should be larger than the interference effect for mixed-list presentation. In mixed-list presentation, differentially valenced words which are presented together should have the effect of diluting any mood manipulating effect of the words. The present study will examine the effects of both happiness-related and anxietyrelated words using mixed-list and blocked presentation.
STUDY 1 Method Subjects A total of 63 subjects participated in the study (38 were female). Their ages ranged from 18 to 46 years (mean of 23.57 years).
Materials and apparatus The stimuli were 20 anxiety-related words, 20 happiness-related words, 20 neutral words matched for length and frequency to the anxiety-related words (anxiety-matched neutrals), and 20 neutral words matched to the happiness-related words (happiness-matched neutrals). These words are presented in Appendix A. An additional set of 80 neutral words were selected for the practice session. A BBC B+ microcomputer controlled stimulus presentation and recorded response latencies and errors.
Design There were two between-subjects factors, group membership (high- vs. low-trait-anxiety), and order of presentation (blocked-trials first vs. mixed-trials first). There were three within-subjects factors ; valence set (anxiety-related vs. happiness-related), emotionality (emotional vs. non-emotional) and type of stimulus presentation (mixed-trial vs. blocked-trial presentation). The mixed trials consisted of a series of trials of differently valenced Stroop words, randomly presented, with four short breaks presented at equal intervals throughout the presentation. The blocked trials consisted of four separate sets of Stroop words, each block consisting of Stroop words of the same valence. The allocation of each stimulus word to either the blocked or the mixed condition was determined randomly for each subject. The order of the blocks was randomly determined for each subject as was the order of the presentation within each block. The colour in which each word was presented (red, green, yellow or blue) was also randomly determined. Subjects were allocated to the conditions randomly until there was a minimum of 10 subjects in each 20
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condition. Each of the 80 stimulus words was presented twice in either the mixed or the blocked condition. The allocation of stimuli to either the mixed or the blocked condition was determined randomly for each subject. This produced a total of 160 trials.
Procedtrre Subjects completed the state and trait versions of the Spielberger State-Trait Anxiety Inventory (STAI; Spielberger, Gorsuch, Lushene, Vagg & Jacobs, 1983) and the Beck Depression Inventory (BDI; Beck, Ward, Mendelson, Mock & Erbaugh, 1961). Subjects scoring 40 and above on the trait form of the STAI were allocated to the high-trait-anxiety group. All other subjects were allocated to the low-traitanxiety group. This cut-off point was decided on the basis of previous studies (e.g. Richards & French, 1990;Richards & Millwood, 1989). Subjects were seated at a BBC B+ microcomputer which presented stimuli and recorded reaction times and errors. Subjects were informed that a series of words would be presented on the screen in different colours, and that words would be presented individually in the centre of the screen. Subjects were instructed to identify the colour of the word (red, green, yellow or blue) by pressing the appropriate key on the computer keyboard. They were instructed to ignore the semantic content of the word, and to respond as quickly as possible whilst maintaining accuracy. Each word remained on the screen until a response was made. There was a 1 s inter-trial interval. Following a practice session consisting of 80 neutral trials, subjects were presented with the mixedtrials first followed by the blocked-trials, or vice versa.
Results A series oft tests was performed on the questionnaire scores for the high- and lowtrait-anxiety groups (see Table 1 for means). It was found that, as expected, the two groups differed in terms of their state anxiety (t(6l) = 6 . 3 4 , ~< .OOl), trait anxiety ( t ( 6 l ) = 13.91,p < .OOl) and depression (t(6l) = 5 . 8 , ~< .OOl). The two groups did not differ in terms of their age (t(6l) = 0.12). Reaction time (RT) difference indices were calculated. The anxiety-related difference index (ARD) was calculated by subtracting the RT to anxiety-matched neutral (AMN) trials from the RT to the anxiety-related (AR) trials. The happinessrelated difference index (HRD) was calculated by subtracting the RT to the happiness-matched neutral (HMN) trials from the R T to the happiness-related (HR) trials. An analysis of variance was performed on these data, with two between-subjects factors (group and order of presentation), and two within-subjects factors (type of presentation and valence of index: ARD vs. HRD). Means and standard deviations of the difference indices are presented in Table 2. This analysis showed that the high-trait group had an overall mean difference score of +29.20 ms, indicating that emotional stimuli took longer to identity than nonemotional stimuli. This was significantly Werent to the mean difference index for the low-trait group of -7.13 ms (F(1,59) = 4 . 8 6 , ~< .05). There was also a main effect of valence, showing a greater mean difference for the ARD index compared to the HRD index (F(1,59) = 6.14, p < .05), with means of +28.82 ms and - 14.40 ms respectively. There was a significant interaction between type of presentation and valence (F(1,59) = 7.13, p < .Ol). However, these effects were modified by the significant interaction between group membership, type of presentation and valence (F(1,59) = 4.53, p < .05). A simple interaction analysis showed that there was
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Table 1. Subject characteristics for Study 1 Anxiety group Measure
Low-trait
High-trait
34.31 34.00 3.79 23.65 39
45.21 47.25 9.29 23.46 24
STAI State
Trait BDI Age N
Note. STAI = Spielberger State-Trait Anxiety Inventory ; BDI = Beck Depression Inventory.
Table 2. Mean difference RTs and standard deviations (in parentheses) for Study 1 Blocked
Mixed
Anxiety group
N
ARD
HRD
ARD
HRD
Low-trait BF
18
-11.01 (140.05) 15.52 (125.72)
-27.11 (170 .OO) -42.57 (145.65)
13.50 (70.75) 9.71 (107.27)
11.94 (100 .OO) -25.76 (128.45)
93.50 (191.30) 163.60 (250.74)
3.36 (164.13) -46.70 (126.56)
- 13.14
13.93 (71.75) 9.80 (82.50)
BS
High-trait BF BS
21 14 10
(61.42) 17.00 (111.77)
Note. BF = Blocked-trials presented first; BS = Blocked-trials presented second ; ARD = Anxietyrelated minus anxiety-matched neutrals ; HRD = Happiness-related minus happiness-matched neutrals.
no interaction between valence of type of presentation for the low-trait group (F(1,59) = 0.48, n.s.). However, there was a significant interaction between valence and type of presentation for the high-trait group (F(1,59) = 4.99, p < .05). This interaction is presented in Fig. 1. Additional analyses showed a significant difference between the two valence indices for blocked presentation (F(1,59) = 8.45, p < .Ol), but not for mixed presentation (F(1,59) = 0.18, n.s.). In order to investigate a possible role of depression and state anxiety in producing interference effects the difference indices were correlated with the personality measures of state anxiety, trait anxiety and depression. In line with the analyses presented above, trait anxiety was significantly correlated with the anxiety-related difference index for the blocked-trials (r = .28, p < .05). There were no other significant correlations.
+
20-2
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140
r
b -40
I
I
I
ARD
HRD
I
Valence
Figure 1. Interaction of type of presentation x valence for high-trait-anxiety subjects in Study 1. RT = reaction time; ARD = anxiety-related difference index; HRD = happiness-related difference index. Presentation 0 , blocked; mixed.
+,
As the error rate was low (3.3 per cent), no analyses were performed on the error data. Discussion The present study has shown that subjects high in trait anxiety took longer to identify the colour of anxiety-related words, even though they were explicitly instructed to ignore the semantic content of the words. This study is in line with previous studies demonstrating a cognitive bias towards the processing of threatrelated stimuli in anxiety. This interference effect was found only for high-trait subjects and only for blocked-trial presentation. From this study it appears that the size of any short-term spreading activation effect was not in itself sufficient to produce significant interference in the high-trait group. Being presented with a block of trials consisting of all anxiety-related words appears to be influential in producing longer reaction times for high-trait subjects. One explanation for this could be that the block of anxiety-related words has a mood manipulating effect for high-trait subjects. However, the happiness-related block of trials failed to produce a corresponding increase in reaction time relative to the happiness-matched neutral block of trials, perhaps indicating that presentation of a block of positive words is insufficient to improve mood even though a block of negative words may induce a negative mood. The failure to demonstrate mixed-trial interference effects appears at first sight to
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be incompatible with previous work as Richards & Millwood (1989) found anxietyrelated effects using a mixed-list paradigm. The present study was based on that of Richards & Millwood in that a computerized Stroop paradigm was employed. However, Richards & Millwood exposed subjects to a mood manipulation procedure prior to performing the emotional Stroop task. This task was unsuccessful in differentially manipulating mood, but state anxiety for all subjects was increased slightly but non-significantly (F(1,34) = 3.54, p < .07), irrespective of the type of mood-manipulation employed. This may have increased arousal generally and been influential in producing mood-congruent interference effects.
STUDY 2 To investigate further the failure to find interference effects using mixed-list presentation, a second study was undertaken which employed a mood manipulation procedure. The manipulation used by Richards & Millwood consisted of presenting subjects with either soluble or insoluble anagrams. However, as this technique was unsuccessful, the present study employed a technique introduced by Richards & Whittaker (1990) which involved the presentation of different types of positive and negative newspaper photographs. This technique has been shown successfully to manipulate self-reported state anxiety levels. The current study is also of theoretical importance as it will allow an examination of state and trait anxiety effects in emotional Stroop interference. Mathews & MacLeod (1985) found correlational evidence for state anxiety accounting for more of the variance than trait anxiety in an emotional Stroop paradigm. On the other hand, Mogg, Mathews & Weinman (1989) found that this interference effect was significantly correlated with trait-anxiety but not state-anxiety scores. Also, Williams & Nulty (1986) found that interference in the colour-naming of negative stimuli reflected stable cognitive biases in depression-prone people rather than transient mood. In an attempt to examine the influence of trait and state anxiety on attention, MacLeod & Mathews (1988) employed a dot detection technique. Students high and low in trait anxiety were given the attentional deployment task 12 weeks before a major examination (when state anxiety was relatively low) and then again just one week before the exam (when state anxiety was relatively high). The authors observed that the high-trait subjects deployed attention toward threat-related material on both occasions, although, for the examination-related stimuli, there was no difference between the two groups 12 weeks before the examination. However, one week before the exam the low-trait subjects showed increased attentional avoidance for the words whereas the high-trait subjects showed an enhanced attentional bias towards them. Mogg, Mathews, Bird & MacGregor-Morris (1990) examined the effects of stress on the processing of threat-related information in high- and low-trait subjects using a colour-naming task and an attentional deployment task. In contrast to MacLeod & Mathews (1988), they found that the selective interference effect of highstress on the colour-naming of the achievement threat words was not related to subjects’ trait levels. They argue for an involvement of both stress and trait anxiety in the processing of threat-related information. In particular, they propose that when stress is prolonged, as in the MacLeod & Mathews study, trait factors may modify
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the attentional bias. However, under acute stress, as in their own study, both highand low-trait subjects are equally affected. Study 2 attempts to examine the effects of state and trait anxiety in a mixed-list Stroop paradigm. Study 1 of Mogg et al. (1990) just failed significantly to influence self-reported state anxiety. The present study will attempt to induce moods using the Richards & Whittaker technique. In addition to this, both MacLeod & Mathews (1988) and Mogg et al. (1990) presented only threat-related and neutral material. The present study presents both anxiety-related and happiness-related stimuli, under both a positive and a negative mood manipulation procedure. This will allow for the possibility of mood-congruent and mood-incongruent processing of both happinessrelated and anxiety-related stimuli. On the basis of MacLeod & Mathews (1988) it is predicted that under increased state anxiety, high-trait individuals should exhibit increased interference, whereas there should be decreased interference for the lowtrait group. If, on the other hand, Mogg et al.’s suggestion that acute stress does not have differential effects on the performance of high- and low-trait anxiety is valid, we would expect interference effects to occur across groups. We intend to examine the effect of increases and decreases in state anxiety on the processing of happiness-related stimuli. Is it the case that high-trait-anxiety subjects’ attentional bias is affected only by increases in stress? The present study will investigate the possibility of a general attentional bias towards information congruent with current emotion in such subjects.
Method SubJects A total of 40 subjects participated in the study, none of whom had participated in Study 1. There were 27 females and 13 males, with ages ranging between 18 and 48 years (mean of 23.82 years).
Materials and apparatus The same stimulus words were used as for Study 1. The six pictures employed by Richards & Whittaker (1990) were used in the mood-manipulationprocedure. Three of the pictures were negative (e.g. violent) and three were positive (e.g. scenic). These photographs had been selected from newspaper articles.
Subjects were presented with only mixed-valence trials. Stimuli were randomly selected from the pool of words in the same way as for Study 1. There were two between-subjects factors: group membership (high- vs. low-trait-anxiety) and mood-manipulation (positive vs. negative). Also, there were two within-subjects factors : valence set (anxiety-related vs. happiness-related) and emotionality (emotional vs. non-emotional). Subjects were assigned to the high- and low-trait-anxietygroups on the basis of trait anxiety scores as in Study 1, and were randomly allocated to the mood-manipulation conditions.
Procedure After completing the state and trait versions of the Spielberger State-Trait Anxiety Inventory and the Beck Depression Inventory, subjects were exposed to either a positive or a negative mood-manipulation procedure. As a rationale for examining the newspaper photographs subjects were informed that the study was investigating the effectiveness of newspaper photography. Subjects were presented with three pleasant or three unpleasant pictures, one at a time, and asked to rate each photograph on (a) whether
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it would attract attention, (6) the professionalism of the photograph, and ( 6 ) its pleasantness/ unpleasantness. A second state anxiety questionnaire was completed at the end of the session. Subjects were thanked for their participation and asked to take part in what they were told was a second study. The procedure for the Stroop session was the same as for Study 1. All subjects were fully debriefed upon completion of the experiment.
Results A summary of subjects’ characteristics is presented in Table 3.
Table 3. Subject characteristics for Study 2 Anxiety group
Low-trait PMM ~
High-trait
NMM
PMM
NMM
29.09 36.18 32.64 4.18 24.64 11
38.70 34.80 46.90 8.10 24.80 10
38.30 40.10 43.70 6.20 22.20 10
~~~
STAI State 1 State 2
Trait BDI Age N
28.89 27.22 30.67 2.56 23.33 9
~~
Note. PMM = Positive mood manipulation; NMM = Negative mood manipulation; STAI = Spielberger State-Trait Anxiety Inventory; State 1 = Pre-mood manipulation score; State 2 = Postmood manipulation score; BDI = Beck Depression Inventory.
A three-way analysis of variance was performed on the scores from the two state questionnaires. This had two between-subjects factors, group membership (high- vs. low-trait-anxiety), and mood-manipulation (positive vs. negative), and one withinsubject factor, occasion of testing (pre- vs. post-manipulation). As expected, the high-trait group had significantly higher average state anxiety scores than the lowtrait group with means of 37.98 and 30.58, respectively (F(1,36) = 9.02, p < .Ol). There was an interaction between type of mood manipulation and occasion of testing (F(1,36) = 10.79, p < .Ol). This showed that after the positive mood-manipulation procedure state anxiety scores decreased from 34.05 to 31.21, whereas state anxiety scores increased from 33.48 to 38.05 after negative mood-manipulation. There were no other main or interaction effects. It therefore appears that the mood manipulation procedure was successful in producing changes in self-reported state anxiety and that this did not interact with group membership. Three two-way analyses of variance, with one between-subjects factor (group membership) and one within-subject factor (mood-manipulation), were performed on the subject characteristic data. The first analysis, performed on the trait scores, showed that as expected the two groups differed in terms of their trait anxiety scores
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(F(1,36) = 68.19, p < .OOl). There were no significant effects involving the mood manipulation factor. The second analysis on the BDI scores showed, as expected, that the high-trait group had significantly higher depression scores than the low-trait group (F(1,36) = 14.82,p < .OOl). Again, there were no significant effects involving the mood manipulation factor. The third analysis showed that the groups did not differ in terms of age. The ARD and HRD indices were calculated in the same way as for Study 1. As the cell variances were heterogeneous a square root transformation was applied (Kirk, t968). (The same pattern of results was obtained from analyses performed on the original data.) The means are presented in their original form in Table 4. Table 4. Mean difference RTs and standard deviations (in parentheses) for Study 2 NMM
PMM Anxiety group Low-trait High-trait
ARD
HRD
ARD
HRD
36.11 (111.10) 0.60 (156.02)
- 5.33 (136.57) 116.60 (225.83)
-24.64
-4.27
(52.11) 72.00 (86.36)
(66.94) -25.30 (28.75)
Note. PMM = Positive mood manipulation ; NMM = Negative mood manipulation; ARD = Anxietyrelated minus anxiety-matchedneutrals ; HRD = Happiness-related minus happiness-matchedneutrals.
An analysis of variance was performed on the transformed difference indices. This had two between-subjects factors ; group (high- vs. low-trait-anxiety) and moodmanipulation (positive vs. negative) and one within-subject factor of valence (ARD vs. HRD). This analysis showed a three-way interaction involving all factors (F(1,36) = 5.29, p < .05). A simple interaction analysis showed a significant interaction between mood manipulation and valence of index for the high-trait group (F(1,36) = 5.22,p < .05) but not for the low-trait group (F(1,36) = 0.87, n.s.). It appears from the above analysis that there is a mood-congruency effect for the high-trait group, in that under positive mood manipulation such subjects show greater interference for happinessrelated words, whereas under negative manipulation there appears to be greater interference for anxiety-related words. No such effects were observed for the lowtrait group. Thus, it appears that where the mood is congruent with the valence of the stimulus (i.e. positive mood and happiness-related words or negative mood and anxietyrelated words) there is interference for the high-trait group. The high-trait group take longer to ignore the Stroop words when the semantic content of the word is congruent with their current mood. When the mood is incongruent with the valence of the stimuli (i.e. positive mood and anxiety-related stimuli or negative mood and happiness-related stimuli) there is a small facilitation effect.
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As in Study 1, the two difference indices were calculated and correlated with the psychometric scores of state anxiety, trait anxiety and depression. The correlations were performed separately for positive and negative mood manipulation. It was found that for the negative mood manipulation trait anxiety correlated significantly with the ARD index (I = .62, p < .Ol). There were no other significant effects. There were too few errors for any meaningful analyses to be performed (1.3 per cent).
+
Discussion Study 2 demonstrated that the mood manipulation procedure was successful in producing predicted changes in self-reported state anxiety. This replicates earlier studies (e.g. Richards & Whittaker, 1990) by demonstrating that presentation of differentially valenced photographs is successful in manipulating self-reported state anxiety. It is also a very quick and simple procedure to implement. In line with previous studies, the nature of the mood manipulation (pleasant or unpleasant) did not interact with group membership. This indicates that the effects of the procedure produced similar changes for high- and low-trait-anxiety subjects. The only difference between the mixed-trial presentation for Study 1 (on first occasion of testing) and Study 2 was the implementation of a mood-manipulation procedure prior to performing the task. Study 2, to some extent, reconciles the findings of non-significant effects for mixed-trial presentation in Study 1 with the Richards & Millwood (1989) study. As stated, Richards & Millwood exposed subjects to a mood-manipulation procedure which had the effect of increasing state anxiety slightly but non-significantly. These increases may have been sufficient to produce mood-congruent interference effects for the high-trait subjects. Blocked presentation in Study 1 may have produced a mood manipulating effect for anxietyrelated material but not for happiness-related material. It can plausibly be argued therefore that mixed-trial presentation will only produce interference effects if hightrait subjects are in an emotional state which differs from their usual baseline state. Furthermore, it is clear from both studies that depression does not appear to play any mediating role. However, as depression was not manipulated in these studies it is not possible to rule out state depression as an important factor. All correlations with depression were non-significant. The correlational analyses support the notion of an interacting effect of state and trait anxiety. Study 2 has shown that subjects high in trait anxiety have an attentional bias towards stimuli which are congruent with their current mood in that they are unable to ignore them, and that low-trait subjects have a tendency in the opposite direction. MacLeod & Mathews (1988) propose that threat-related material shows an enhanced ability to capture the selective system in anxious individuals. The present study offers support for this hypothesis. However, it appears from the present data that this is not restricted to threat-related material. It appears that subjects high in trait anxiety have greater susceptibility for stimuli congruent with their mood. There was no such susceptibility for low-trait subjects. This finding does not fit with Bower’s model which would predict that there should be mood congruent effects for both high- and low-trait-anxiety subjects. It also does not fit easily with MacLeod &
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Mathews’ suggestions, whose hypotheses are limited to threat-related attentional biases. MacLeod & Mathews (1988) found equivalent increases in levels of state anxiety across their two experimental sessions (12 weeks and one week before examination) which were associated with different effects for the two groups. Consistent with this is the finding from our Study 2 of equivalent increases and decreases in state anxiety which were associated with different patterns of results. Mogg e t a/. (1990) suggested that it may have been the prolonged stress to which subjects in MacLeod & Mathews’ (1988) study were subjected, which modified the high- and low-trait subjects’ performance on the dot detection task whereas the acute stress employed in their own study affected high- and low-anxiety subjects equally. The present results show that acute mood manipulations can have different effects on high- and low-anxiety subjects, undermining Mogg et al.’s suggestion. However, there are major methodological differences between the experiments which could account for the discrepant results. The present investigation used a computerized Stroop task together with a manual response, whereas Mogg et al. (1990) used Stroop words presented on cards together with a vocal response. Further research is needed to resolve these issues. References Beck, A. T., Ward, C. H., Mendelson, M., Mock, J. E. & Erbaugh, J. K. (1961). An inventory for measuring depression. Archives of General Psychiatry, 4, 561-571. Bower, G. H. (1981). Mood and memory. American Psychologist, 36, 129-148. Bower, G. H. & Mayer, J. D. (1985). Failure to replicate mood-dependent retrieval. Bulletin of the Psychonomic Society, 23, 3 9 4 2 . Bower, G. H. & Mayer, J. D. (1989). In search of mood-dependent retrieval. Journal of Social Behaviour and Personality, 4, 121-156. Eysenck, M. W., MacLeod, C. & Mathews, A. (1987). Cognitive functioning and anxiety. Psychological Research, 49, 189-1 95. Kirk, R. E. (1968). Experimental Design: Proceduresfor the Behavioral Sciences. Monterey, CA: Basic Books. MacLeod, C. (1990). Mood disorders and cognition. In M. W. Eysenck (Ed.), Cognitive Psychology: A n International Review, pp. 9-56. Chichester : Wiley. MacLeod, C. & Mathews, A. (1988). Anxiety and allocation of attention to threat. Quarter4 Journal of Experimental Psychology, MA, 653-670. Mathews, A. & MacLeod, C. (1985). Selective processing of threat cues in anxiety states. Behavior Research and Therapy, 23, 563-569. Meyer, D. E. & Schvaneveldt, R. W. (1971). Facilitation in recognizing pairs of words: Evidence of a dependence between retrieval functions. Journal of Experimental Psychology, 90, 227-234. Mogg, K., Mathews, A., Bird, C. & MacGregor-Morris, R. (1990). Effects of stress and anxiety on the processing of threat stimuli. Journal of Personalig and Social Psychology, 39, 1230-1237. Mogg, K., Mathews, A. & Weinman, J. (1989). Memory bias in clinical anxiety. Journal of Abnormal Psychology, 96, 94-98. Neely, J. H. (1976). Semantic priming and retrieval from lexical memory: Evidence for facilitatory and inhibitory processes. Memory and Cognition, 4, 648-654. Neely, J. H. (1977). Semantic priming and retrieval from lexical memory: Role of inhibitionless spreading activation and limited-capacity attention. Journal of Experimental Psychology :General, 106, 226-254. Ratcliff, R. & McKoon, G. (1981). Does activation really spread? Psychological Review, 88, 454-462. Ray, C. (1979). Examination stress and performance on a color-word interference test. Perceptual and Motor Skills, 49, 400-402.
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Richards, A. & French, C. C. (1990). Central versus peripheral presentation of stimuli in an emotional Stroop task. Anxiety Research, 3, 41-49. Richards, A. & Millwood, B. (1989). Colour-identification of differentially valenced words in anxiety. Cognition and Emotion, 3, 171-176. Richards, A. & Whittaker, T. M. (1990). Effects of anxiety and mood manipulation in autobiographical memory. British Journal of Clinical Psychology, 29, 145-1 53. Spielberger, C. D., Gorsuch, R. L., Lushene, R., Vagg, P. R. & Jacobs, G. A. (1983). Manual for the State-Trait Anxiety Inventor_y(Form Y ) .Palo Alto, CA : Consulting Psychologists Press. Stanovich, K. E. & West, R. F. (1979). Mechanisms of sentence context effects in reading: Automatic activation and conscious attention. Memory and Cognition, 7 , 77-85. Stanovich, K. E. & West, R. F. (1981). The effects of sentence context on ongoing word recognition: Tests of a two-process theory. Journal of Experimental Psychology :Human Perception and Performance, 7 , 658-672. Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18, 643-662. Watts, F. N., McKenna, F. P., Sharrock, R. & Trezise, L. (1986). Colour-naming of phobic-related words. British Journal of Psychology, 77, 97-1 08. Williams, J. M. G. & Broadbent, K. (1986). Distraction by emotional stimuli: Use of a Stroop task with suicide attempters. British Journal of Clinical Psychology, 25, 101-1 10. Williams, J. M. G. & Nulty, D. D. (1986). Construct accessibility, depression and the emotional Stroop task : Transient mood or stable structure? Personality and Individual Differences, 7 , 485-491. Williams, J. M. G., Watts, F. N., MacLeod, C. & Mathews, A. (1988). Cognitive Psychology and Emotional Disorders. Chichester : Wiley. Received 21 May 1990; revised version received 28 January 1992
Appendix A. Words used in studies AR
AMN
HR
HMN
Weak Worried Agony Panicky Failure Nervous Helpless Terrified Painful Die Sickness Disease Tragedy Accident Suffering Cancer Paralysed Despair Distressed Coffin
Take Bramble Verse Section Clothes Picture Interest Margarine Around CUP Material Library Whistle Instead Something Taller Expensive Service Understand Lesser
Optimistic Love Brave Successful Reassured Confident Strength Pleasure Happiness Ecstasy Healthy Homely Laughter Warmth Overjoyed Friend 1y Security Capable
Typewriter Ring Stick Profession Carpenter Cardboard Bu i1ding Magnetic Associate Grounds Climate System Inventor Corner Offspring Alphabet Para 11e1 Measure Cord Lighter
Good Relaxed
Note. AR = anxiety-related; AMN = anxiety-matched neutral; HR = happiness-related; HMN = happiness-matched neutral.
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0 1992 The British Psychological Society
Effects of mood manipulation and anxiety on performance of an emotional Stroop task Anne Richards* Department of Pgcbology, Birkbeck College, Universig of London, Malet Street, London WClE 7HX, UK
Christopher C. French, Wendy Johnson, Jennifer Naparstek and Jane Williams Goldsmitbs’ College, University of London In Study 1 subjects high and low in trait anxiety were asked to identify the colour of anxiety-related, anxiety-matched neutral, happiness-related and happinessmatched neutral words. There were two types of stimulus presentation : blocked trials, where stimuli were blocked with respect to their valence, and mixed trials, where stimuli were mixed with respect to their valence. Subjects high in trait anxiety took longer to identify the colour of anxiety-related compared to matched neutral words for blocked-trial presentation only. In Study 2 subjects were exposed to either a positive or a negative mood-manipulation followed by a mixed-trial Stroop task. The mood manipulation procedure was successful in producing predicted changes in self-reported state anxiety. Analyses showed that high-trait-anxiety subjects exhibited interference effects consistent with the induced mood. No such effects were observed for the low-trait-anxiety subjects.
It has now been established beyond reasonable doubt that there are differences in information processing by anxious compared to non-anxious individuals. Research has examined both clinical and normal populations. Bower’s (1981) model proposes that subjects high in anxiety should have perceptual sensitivity for threat-related information. This model proposes that each distinct emotion has an emotion node in semantic memory. Emotion nodes may be activated by a variety of stimuli including symbolic verbal cues and physiological cues. Activation spreads from these nodes, resulting in increased activation in associated nodes. This model predicts that emotion will enhance the salience of mood-congruent material, resulting in an increase in perceptual sensitivity for that material. The model also predicts that there should be mood-dependent retrieval. The evidence for this latter prediction has been equivocal (e.g. Bower & Mayer, 1985, 1989). However, there has been a great deal of support for the former prediction. Research has clearly indicated that high-anxiety subjects have a selective attentional bias for threatening information (for reviews see Eysenck, MacLeod & Mathews, 1987; MacLeod, 1990; Williams, Watts, MacLeod & Mathews, 1988). Several studies have used a modified version of the Stroop paradigm (Stroop, * Requests for reprints.
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1935) to examine cognitive processes in anxiety. The classic paradigm involves presenting a subject with colour words written in different coloured inks. The subject’s task is to identify the colour of the ink whilst ignoring the semantic content of the word. When the colour of the ink is congruent with the word (e.g. ‘blue’ written in blue ink), the time taken to name the colour of the word is reduced compared to identifying the colour of a row of Xs. Conversely, on incongruent trials (e.g. ‘red’ written in blue ink), colours are named more slowly than for a row of Xs. The modified paradigm involves the presentation of emotional and non-emotional words in different coloured inks, and the task of the subject is to identify their colour. For example, an emotional word such as ‘mutilate ’ may be presented in say, red, and the task of the subject is to say ‘red’. Bower’s (1981) prediction of mood-congruent interference effects using the Stroop paradigm has generally been supported. Ray (1979) found that pre-examination students took longer to name the colour of examination-related Stroop words compared to matched-neutral words. Mood congruent interference effects were demonstrated by Mathews & MacLeod (1985) using clinically anxious patients, and by Williams & Broadbent (1986) with a sample of overdose patients, and by Watts, McKenna, Sharrock & Trezise (1986) with spider-phobics. All the above studies have presented Stroop words on cards. The subjects begin at the top left corner and speak out loud the colour names of the words. The cards contain words of all the same hedonic tone, that is, the cards consist entirely of threatening words or entirely of neutral words. Richards & Millwood (1989) departed from the standard paradigm in several ways. Firstly, a computer was used to present stimuli. Secondly, a manual as opposed to the more usual vocal response was required, and thirdly, words were presented individually on the screen. In the typical emotional Stroop paradigm response latencies reflect the time taken to identify a series of colour-words, including those trials on which errors were made. The computerized version differentiates between correct and incorrect responses. Richards & Millwood (1989) found that whereas low-trait-anxious subjects were unaffected by the hedonic tone of the stimulus words, high-trait-anxious subjects took longest to identify the colour of threat-related material and were quickest at identifying the colour of pleasant words. This study used trials mixed with respect to their valence. That is, each word could have been either threat-related, pleasant or neutral, and subjects could not predict the valence on a trial-to-trial basis. Richards & French (1990) used the computerized emotional Stroop paradigm with blocked presentation and found that high-trait-anxious subjects took longer to identify the colour of anxiety-related compared to matched neutral words. The present study directly compares the effects of presenting stimuli randomly mixed with respect to their valence with presenting stimuli blocked with respect to their valence. Neely (1976, 1977) and Stanovich & West (1979, 1981) put forward a two-process model of word recognition in which the first stage of lexical access is viewed as a process of automatic spreading activation. This is then followed by a second, optional, stage whereby there is a strategic allocation of limited capacity resources. The spreading activation effect appears very rapidly, reaching asymptotic levels in about 200 ms (Meyer & Schvaneveldt, 1971; Ratcliff & McKoon, 1981).
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If the interference effect for threat-related Stroop words is due to short-term automatic spreading activation we would expect comparable interference effects for both mixed-list and blocked presentation for high-trait subjects. This is because interference effects should occur on a trial-to-trial basis and dissipate prior to the onset of the next trial. On the other hand, if there are longer-lasting effects such as a mood manipulating effect of the words themselves, then we might expect there to be greater interference for blocked presentation compared to mixed-list presentation. Mood may build up across a block of emotional words but be unaffected by a block of neutral words. For example, high-trait-anxiety subjects may take longer to identify the colour of anxietyrelated words when they are presented under blocked conditions because the mood manipulating effect of the words themselves has an interfering effect. Thus, the interference effect for blocked presentation, as measured by the difference in reaction time to the anxiety-related block compared to the neutral block, should be larger than the interference effect for mixed-list presentation. In mixed-list presentation, differentially valenced words which are presented together should have the effect of diluting any mood manipulating effect of the words. The present study will examine the effects of both happiness-related and anxietyrelated words using mixed-list and blocked presentation.
STUDY 1 Method Subjects A total of 63 subjects participated in the study (38 were female). Their ages ranged from 18 to 46 years (mean of 23.57 years).
Materials and apparatus The stimuli were 20 anxiety-related words, 20 happiness-related words, 20 neutral words matched for length and frequency to the anxiety-related words (anxiety-matched neutrals), and 20 neutral words matched to the happiness-related words (happiness-matched neutrals). These words are presented in Appendix A. An additional set of 80 neutral words were selected for the practice session. A BBC B+ microcomputer controlled stimulus presentation and recorded response latencies and errors.
Design There were two between-subjects factors, group membership (high- vs. low-trait-anxiety), and order of presentation (blocked-trials first vs. mixed-trials first). There were three within-subjects factors ; valence set (anxiety-related vs. happiness-related), emotionality (emotional vs. non-emotional) and type of stimulus presentation (mixed-trial vs. blocked-trial presentation). The mixed trials consisted of a series of trials of differently valenced Stroop words, randomly presented, with four short breaks presented at equal intervals throughout the presentation. The blocked trials consisted of four separate sets of Stroop words, each block consisting of Stroop words of the same valence. The allocation of each stimulus word to either the blocked or the mixed condition was determined randomly for each subject. The order of the blocks was randomly determined for each subject as was the order of the presentation within each block. The colour in which each word was presented (red, green, yellow or blue) was also randomly determined. Subjects were allocated to the conditions randomly until there was a minimum of 10 subjects in each 20
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condition. Each of the 80 stimulus words was presented twice in either the mixed or the blocked condition. The allocation of stimuli to either the mixed or the blocked condition was determined randomly for each subject. This produced a total of 160 trials.
Procedtrre Subjects completed the state and trait versions of the Spielberger State-Trait Anxiety Inventory (STAI; Spielberger, Gorsuch, Lushene, Vagg & Jacobs, 1983) and the Beck Depression Inventory (BDI; Beck, Ward, Mendelson, Mock & Erbaugh, 1961). Subjects scoring 40 and above on the trait form of the STAI were allocated to the high-trait-anxiety group. All other subjects were allocated to the low-traitanxiety group. This cut-off point was decided on the basis of previous studies (e.g. Richards & French, 1990;Richards & Millwood, 1989). Subjects were seated at a BBC B+ microcomputer which presented stimuli and recorded reaction times and errors. Subjects were informed that a series of words would be presented on the screen in different colours, and that words would be presented individually in the centre of the screen. Subjects were instructed to identify the colour of the word (red, green, yellow or blue) by pressing the appropriate key on the computer keyboard. They were instructed to ignore the semantic content of the word, and to respond as quickly as possible whilst maintaining accuracy. Each word remained on the screen until a response was made. There was a 1 s inter-trial interval. Following a practice session consisting of 80 neutral trials, subjects were presented with the mixedtrials first followed by the blocked-trials, or vice versa.
Results A series oft tests was performed on the questionnaire scores for the high- and lowtrait-anxiety groups (see Table 1 for means). It was found that, as expected, the two groups differed in terms of their state anxiety (t(6l) = 6 . 3 4 , ~< .OOl), trait anxiety ( t ( 6 l ) = 13.91,p < .OOl) and depression (t(6l) = 5 . 8 , ~< .OOl). The two groups did not differ in terms of their age (t(6l) = 0.12). Reaction time (RT) difference indices were calculated. The anxiety-related difference index (ARD) was calculated by subtracting the RT to anxiety-matched neutral (AMN) trials from the RT to the anxiety-related (AR) trials. The happinessrelated difference index (HRD) was calculated by subtracting the RT to the happiness-matched neutral (HMN) trials from the R T to the happiness-related (HR) trials. An analysis of variance was performed on these data, with two between-subjects factors (group and order of presentation), and two within-subjects factors (type of presentation and valence of index: ARD vs. HRD). Means and standard deviations of the difference indices are presented in Table 2. This analysis showed that the high-trait group had an overall mean difference score of +29.20 ms, indicating that emotional stimuli took longer to identity than nonemotional stimuli. This was significantly Werent to the mean difference index for the low-trait group of -7.13 ms (F(1,59) = 4 . 8 6 , ~< .05). There was also a main effect of valence, showing a greater mean difference for the ARD index compared to the HRD index (F(1,59) = 6.14, p < .05), with means of +28.82 ms and - 14.40 ms respectively. There was a significant interaction between type of presentation and valence (F(1,59) = 7.13, p < .Ol). However, these effects were modified by the significant interaction between group membership, type of presentation and valence (F(1,59) = 4.53, p < .05). A simple interaction analysis showed that there was
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Table 1. Subject characteristics for Study 1 Anxiety group Measure
Low-trait
High-trait
34.31 34.00 3.79 23.65 39
45.21 47.25 9.29 23.46 24
STAI State
Trait BDI Age N
Note. STAI = Spielberger State-Trait Anxiety Inventory ; BDI = Beck Depression Inventory.
Table 2. Mean difference RTs and standard deviations (in parentheses) for Study 1 Blocked
Mixed
Anxiety group
N
ARD
HRD
ARD
HRD
Low-trait BF
18
-11.01 (140.05) 15.52 (125.72)
-27.11 (170 .OO) -42.57 (145.65)
13.50 (70.75) 9.71 (107.27)
11.94 (100 .OO) -25.76 (128.45)
93.50 (191.30) 163.60 (250.74)
3.36 (164.13) -46.70 (126.56)
- 13.14
13.93 (71.75) 9.80 (82.50)
BS
High-trait BF BS
21 14 10
(61.42) 17.00 (111.77)
Note. BF = Blocked-trials presented first; BS = Blocked-trials presented second ; ARD = Anxietyrelated minus anxiety-matched neutrals ; HRD = Happiness-related minus happiness-matched neutrals.
no interaction between valence of type of presentation for the low-trait group (F(1,59) = 0.48, n.s.). However, there was a significant interaction between valence and type of presentation for the high-trait group (F(1,59) = 4.99, p < .05). This interaction is presented in Fig. 1. Additional analyses showed a significant difference between the two valence indices for blocked presentation (F(1,59) = 8.45, p < .Ol), but not for mixed presentation (F(1,59) = 0.18, n.s.). In order to investigate a possible role of depression and state anxiety in producing interference effects the difference indices were correlated with the personality measures of state anxiety, trait anxiety and depression. In line with the analyses presented above, trait anxiety was significantly correlated with the anxiety-related difference index for the blocked-trials (r = .28, p < .05). There were no other significant correlations.
+
20-2
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140
r
b -40
I
I
I
ARD
HRD
I
Valence
Figure 1. Interaction of type of presentation x valence for high-trait-anxiety subjects in Study 1. RT = reaction time; ARD = anxiety-related difference index; HRD = happiness-related difference index. Presentation 0 , blocked; mixed.
+,
As the error rate was low (3.3 per cent), no analyses were performed on the error data. Discussion The present study has shown that subjects high in trait anxiety took longer to identify the colour of anxiety-related words, even though they were explicitly instructed to ignore the semantic content of the words. This study is in line with previous studies demonstrating a cognitive bias towards the processing of threatrelated stimuli in anxiety. This interference effect was found only for high-trait subjects and only for blocked-trial presentation. From this study it appears that the size of any short-term spreading activation effect was not in itself sufficient to produce significant interference in the high-trait group. Being presented with a block of trials consisting of all anxiety-related words appears to be influential in producing longer reaction times for high-trait subjects. One explanation for this could be that the block of anxiety-related words has a mood manipulating effect for high-trait subjects. However, the happiness-related block of trials failed to produce a corresponding increase in reaction time relative to the happiness-matched neutral block of trials, perhaps indicating that presentation of a block of positive words is insufficient to improve mood even though a block of negative words may induce a negative mood. The failure to demonstrate mixed-trial interference effects appears at first sight to
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be incompatible with previous work as Richards & Millwood (1989) found anxietyrelated effects using a mixed-list paradigm. The present study was based on that of Richards & Millwood in that a computerized Stroop paradigm was employed. However, Richards & Millwood exposed subjects to a mood manipulation procedure prior to performing the emotional Stroop task. This task was unsuccessful in differentially manipulating mood, but state anxiety for all subjects was increased slightly but non-significantly (F(1,34) = 3.54, p < .07), irrespective of the type of mood-manipulation employed. This may have increased arousal generally and been influential in producing mood-congruent interference effects.
STUDY 2 To investigate further the failure to find interference effects using mixed-list presentation, a second study was undertaken which employed a mood manipulation procedure. The manipulation used by Richards & Millwood consisted of presenting subjects with either soluble or insoluble anagrams. However, as this technique was unsuccessful, the present study employed a technique introduced by Richards & Whittaker (1990) which involved the presentation of different types of positive and negative newspaper photographs. This technique has been shown successfully to manipulate self-reported state anxiety levels. The current study is also of theoretical importance as it will allow an examination of state and trait anxiety effects in emotional Stroop interference. Mathews & MacLeod (1985) found correlational evidence for state anxiety accounting for more of the variance than trait anxiety in an emotional Stroop paradigm. On the other hand, Mogg, Mathews & Weinman (1989) found that this interference effect was significantly correlated with trait-anxiety but not state-anxiety scores. Also, Williams & Nulty (1986) found that interference in the colour-naming of negative stimuli reflected stable cognitive biases in depression-prone people rather than transient mood. In an attempt to examine the influence of trait and state anxiety on attention, MacLeod & Mathews (1988) employed a dot detection technique. Students high and low in trait anxiety were given the attentional deployment task 12 weeks before a major examination (when state anxiety was relatively low) and then again just one week before the exam (when state anxiety was relatively high). The authors observed that the high-trait subjects deployed attention toward threat-related material on both occasions, although, for the examination-related stimuli, there was no difference between the two groups 12 weeks before the examination. However, one week before the exam the low-trait subjects showed increased attentional avoidance for the words whereas the high-trait subjects showed an enhanced attentional bias towards them. Mogg, Mathews, Bird & MacGregor-Morris (1990) examined the effects of stress on the processing of threat-related information in high- and low-trait subjects using a colour-naming task and an attentional deployment task. In contrast to MacLeod & Mathews (1988), they found that the selective interference effect of highstress on the colour-naming of the achievement threat words was not related to subjects’ trait levels. They argue for an involvement of both stress and trait anxiety in the processing of threat-related information. In particular, they propose that when stress is prolonged, as in the MacLeod & Mathews study, trait factors may modify
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the attentional bias. However, under acute stress, as in their own study, both highand low-trait subjects are equally affected. Study 2 attempts to examine the effects of state and trait anxiety in a mixed-list Stroop paradigm. Study 1 of Mogg et al. (1990) just failed significantly to influence self-reported state anxiety. The present study will attempt to induce moods using the Richards & Whittaker technique. In addition to this, both MacLeod & Mathews (1988) and Mogg et al. (1990) presented only threat-related and neutral material. The present study presents both anxiety-related and happiness-related stimuli, under both a positive and a negative mood manipulation procedure. This will allow for the possibility of mood-congruent and mood-incongruent processing of both happinessrelated and anxiety-related stimuli. On the basis of MacLeod & Mathews (1988) it is predicted that under increased state anxiety, high-trait individuals should exhibit increased interference, whereas there should be decreased interference for the lowtrait group. If, on the other hand, Mogg et al.’s suggestion that acute stress does not have differential effects on the performance of high- and low-trait anxiety is valid, we would expect interference effects to occur across groups. We intend to examine the effect of increases and decreases in state anxiety on the processing of happiness-related stimuli. Is it the case that high-trait-anxiety subjects’ attentional bias is affected only by increases in stress? The present study will investigate the possibility of a general attentional bias towards information congruent with current emotion in such subjects.
Method SubJects A total of 40 subjects participated in the study, none of whom had participated in Study 1. There were 27 females and 13 males, with ages ranging between 18 and 48 years (mean of 23.82 years).
Materials and apparatus The same stimulus words were used as for Study 1. The six pictures employed by Richards & Whittaker (1990) were used in the mood-manipulationprocedure. Three of the pictures were negative (e.g. violent) and three were positive (e.g. scenic). These photographs had been selected from newspaper articles.
Subjects were presented with only mixed-valence trials. Stimuli were randomly selected from the pool of words in the same way as for Study 1. There were two between-subjects factors: group membership (high- vs. low-trait-anxiety) and mood-manipulation (positive vs. negative). Also, there were two within-subjects factors : valence set (anxiety-related vs. happiness-related) and emotionality (emotional vs. non-emotional). Subjects were assigned to the high- and low-trait-anxietygroups on the basis of trait anxiety scores as in Study 1, and were randomly allocated to the mood-manipulation conditions.
Procedure After completing the state and trait versions of the Spielberger State-Trait Anxiety Inventory and the Beck Depression Inventory, subjects were exposed to either a positive or a negative mood-manipulation procedure. As a rationale for examining the newspaper photographs subjects were informed that the study was investigating the effectiveness of newspaper photography. Subjects were presented with three pleasant or three unpleasant pictures, one at a time, and asked to rate each photograph on (a) whether
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it would attract attention, (6) the professionalism of the photograph, and ( 6 ) its pleasantness/ unpleasantness. A second state anxiety questionnaire was completed at the end of the session. Subjects were thanked for their participation and asked to take part in what they were told was a second study. The procedure for the Stroop session was the same as for Study 1. All subjects were fully debriefed upon completion of the experiment.
Results A summary of subjects’ characteristics is presented in Table 3.
Table 3. Subject characteristics for Study 2 Anxiety group
Low-trait PMM ~
High-trait
NMM
PMM
NMM
29.09 36.18 32.64 4.18 24.64 11
38.70 34.80 46.90 8.10 24.80 10
38.30 40.10 43.70 6.20 22.20 10
~~~
STAI State 1 State 2
Trait BDI Age N
28.89 27.22 30.67 2.56 23.33 9
~~
Note. PMM = Positive mood manipulation; NMM = Negative mood manipulation; STAI = Spielberger State-Trait Anxiety Inventory; State 1 = Pre-mood manipulation score; State 2 = Postmood manipulation score; BDI = Beck Depression Inventory.
A three-way analysis of variance was performed on the scores from the two state questionnaires. This had two between-subjects factors, group membership (high- vs. low-trait-anxiety), and mood-manipulation (positive vs. negative), and one withinsubject factor, occasion of testing (pre- vs. post-manipulation). As expected, the high-trait group had significantly higher average state anxiety scores than the lowtrait group with means of 37.98 and 30.58, respectively (F(1,36) = 9.02, p < .Ol). There was an interaction between type of mood manipulation and occasion of testing (F(1,36) = 10.79, p < .Ol). This showed that after the positive mood-manipulation procedure state anxiety scores decreased from 34.05 to 31.21, whereas state anxiety scores increased from 33.48 to 38.05 after negative mood-manipulation. There were no other main or interaction effects. It therefore appears that the mood manipulation procedure was successful in producing changes in self-reported state anxiety and that this did not interact with group membership. Three two-way analyses of variance, with one between-subjects factor (group membership) and one within-subject factor (mood-manipulation), were performed on the subject characteristic data. The first analysis, performed on the trait scores, showed that as expected the two groups differed in terms of their trait anxiety scores
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(F(1,36) = 68.19, p < .OOl). There were no significant effects involving the mood manipulation factor. The second analysis on the BDI scores showed, as expected, that the high-trait group had significantly higher depression scores than the low-trait group (F(1,36) = 14.82,p < .OOl). Again, there were no significant effects involving the mood manipulation factor. The third analysis showed that the groups did not differ in terms of age. The ARD and HRD indices were calculated in the same way as for Study 1. As the cell variances were heterogeneous a square root transformation was applied (Kirk, t968). (The same pattern of results was obtained from analyses performed on the original data.) The means are presented in their original form in Table 4. Table 4. Mean difference RTs and standard deviations (in parentheses) for Study 2 NMM
PMM Anxiety group Low-trait High-trait
ARD
HRD
ARD
HRD
36.11 (111.10) 0.60 (156.02)
- 5.33 (136.57) 116.60 (225.83)
-24.64
-4.27
(52.11) 72.00 (86.36)
(66.94) -25.30 (28.75)
Note. PMM = Positive mood manipulation ; NMM = Negative mood manipulation; ARD = Anxietyrelated minus anxiety-matchedneutrals ; HRD = Happiness-related minus happiness-matchedneutrals.
An analysis of variance was performed on the transformed difference indices. This had two between-subjects factors ; group (high- vs. low-trait-anxiety) and moodmanipulation (positive vs. negative) and one within-subject factor of valence (ARD vs. HRD). This analysis showed a three-way interaction involving all factors (F(1,36) = 5.29, p < .05). A simple interaction analysis showed a significant interaction between mood manipulation and valence of index for the high-trait group (F(1,36) = 5.22,p < .05) but not for the low-trait group (F(1,36) = 0.87, n.s.). It appears from the above analysis that there is a mood-congruency effect for the high-trait group, in that under positive mood manipulation such subjects show greater interference for happinessrelated words, whereas under negative manipulation there appears to be greater interference for anxiety-related words. No such effects were observed for the lowtrait group. Thus, it appears that where the mood is congruent with the valence of the stimulus (i.e. positive mood and happiness-related words or negative mood and anxietyrelated words) there is interference for the high-trait group. The high-trait group take longer to ignore the Stroop words when the semantic content of the word is congruent with their current mood. When the mood is incongruent with the valence of the stimuli (i.e. positive mood and anxiety-related stimuli or negative mood and happiness-related stimuli) there is a small facilitation effect.
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As in Study 1, the two difference indices were calculated and correlated with the psychometric scores of state anxiety, trait anxiety and depression. The correlations were performed separately for positive and negative mood manipulation. It was found that for the negative mood manipulation trait anxiety correlated significantly with the ARD index (I = .62, p < .Ol). There were no other significant effects. There were too few errors for any meaningful analyses to be performed (1.3 per cent).
+
Discussion Study 2 demonstrated that the mood manipulation procedure was successful in producing predicted changes in self-reported state anxiety. This replicates earlier studies (e.g. Richards & Whittaker, 1990) by demonstrating that presentation of differentially valenced photographs is successful in manipulating self-reported state anxiety. It is also a very quick and simple procedure to implement. In line with previous studies, the nature of the mood manipulation (pleasant or unpleasant) did not interact with group membership. This indicates that the effects of the procedure produced similar changes for high- and low-trait-anxiety subjects. The only difference between the mixed-trial presentation for Study 1 (on first occasion of testing) and Study 2 was the implementation of a mood-manipulation procedure prior to performing the task. Study 2, to some extent, reconciles the findings of non-significant effects for mixed-trial presentation in Study 1 with the Richards & Millwood (1989) study. As stated, Richards & Millwood exposed subjects to a mood-manipulation procedure which had the effect of increasing state anxiety slightly but non-significantly. These increases may have been sufficient to produce mood-congruent interference effects for the high-trait subjects. Blocked presentation in Study 1 may have produced a mood manipulating effect for anxietyrelated material but not for happiness-related material. It can plausibly be argued therefore that mixed-trial presentation will only produce interference effects if hightrait subjects are in an emotional state which differs from their usual baseline state. Furthermore, it is clear from both studies that depression does not appear to play any mediating role. However, as depression was not manipulated in these studies it is not possible to rule out state depression as an important factor. All correlations with depression were non-significant. The correlational analyses support the notion of an interacting effect of state and trait anxiety. Study 2 has shown that subjects high in trait anxiety have an attentional bias towards stimuli which are congruent with their current mood in that they are unable to ignore them, and that low-trait subjects have a tendency in the opposite direction. MacLeod & Mathews (1988) propose that threat-related material shows an enhanced ability to capture the selective system in anxious individuals. The present study offers support for this hypothesis. However, it appears from the present data that this is not restricted to threat-related material. It appears that subjects high in trait anxiety have greater susceptibility for stimuli congruent with their mood. There was no such susceptibility for low-trait subjects. This finding does not fit with Bower’s model which would predict that there should be mood congruent effects for both high- and low-trait-anxiety subjects. It also does not fit easily with MacLeod &
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Anne Richards and others
Mathews’ suggestions, whose hypotheses are limited to threat-related attentional biases. MacLeod & Mathews (1988) found equivalent increases in levels of state anxiety across their two experimental sessions (12 weeks and one week before examination) which were associated with different effects for the two groups. Consistent with this is the finding from our Study 2 of equivalent increases and decreases in state anxiety which were associated with different patterns of results. Mogg e t a/. (1990) suggested that it may have been the prolonged stress to which subjects in MacLeod & Mathews’ (1988) study were subjected, which modified the high- and low-trait subjects’ performance on the dot detection task whereas the acute stress employed in their own study affected high- and low-anxiety subjects equally. The present results show that acute mood manipulations can have different effects on high- and low-anxiety subjects, undermining Mogg et al.’s suggestion. However, there are major methodological differences between the experiments which could account for the discrepant results. The present investigation used a computerized Stroop task together with a manual response, whereas Mogg et al. (1990) used Stroop words presented on cards together with a vocal response. Further research is needed to resolve these issues. References Beck, A. T., Ward, C. H., Mendelson, M., Mock, J. E. & Erbaugh, J. K. (1961). An inventory for measuring depression. Archives of General Psychiatry, 4, 561-571. Bower, G. H. (1981). Mood and memory. American Psychologist, 36, 129-148. Bower, G. H. & Mayer, J. D. (1985). Failure to replicate mood-dependent retrieval. Bulletin of the Psychonomic Society, 23, 3 9 4 2 . Bower, G. H. & Mayer, J. D. (1989). In search of mood-dependent retrieval. Journal of Social Behaviour and Personality, 4, 121-156. Eysenck, M. W., MacLeod, C. & Mathews, A. (1987). Cognitive functioning and anxiety. Psychological Research, 49, 189-1 95. Kirk, R. E. (1968). Experimental Design: Proceduresfor the Behavioral Sciences. Monterey, CA: Basic Books. MacLeod, C. (1990). Mood disorders and cognition. In M. W. Eysenck (Ed.), Cognitive Psychology: A n International Review, pp. 9-56. Chichester : Wiley. MacLeod, C. & Mathews, A. (1988). Anxiety and allocation of attention to threat. Quarter4 Journal of Experimental Psychology, MA, 653-670. Mathews, A. & MacLeod, C. (1985). Selective processing of threat cues in anxiety states. Behavior Research and Therapy, 23, 563-569. Meyer, D. E. & Schvaneveldt, R. W. (1971). Facilitation in recognizing pairs of words: Evidence of a dependence between retrieval functions. Journal of Experimental Psychology, 90, 227-234. Mogg, K., Mathews, A., Bird, C. & MacGregor-Morris, R. (1990). Effects of stress and anxiety on the processing of threat stimuli. Journal of Personalig and Social Psychology, 39, 1230-1237. Mogg, K., Mathews, A. & Weinman, J. (1989). Memory bias in clinical anxiety. Journal of Abnormal Psychology, 96, 94-98. Neely, J. H. (1976). Semantic priming and retrieval from lexical memory: Evidence for facilitatory and inhibitory processes. Memory and Cognition, 4, 648-654. Neely, J. H. (1977). Semantic priming and retrieval from lexical memory: Role of inhibitionless spreading activation and limited-capacity attention. Journal of Experimental Psychology :General, 106, 226-254. Ratcliff, R. & McKoon, G. (1981). Does activation really spread? Psychological Review, 88, 454-462. Ray, C. (1979). Examination stress and performance on a color-word interference test. Perceptual and Motor Skills, 49, 400-402.
Effects of mood manipulation and anxiety
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Richards, A. & French, C. C. (1990). Central versus peripheral presentation of stimuli in an emotional Stroop task. Anxiety Research, 3, 41-49. Richards, A. & Millwood, B. (1989). Colour-identification of differentially valenced words in anxiety. Cognition and Emotion, 3, 171-176. Richards, A. & Whittaker, T. M. (1990). Effects of anxiety and mood manipulation in autobiographical memory. British Journal of Clinical Psychology, 29, 145-1 53. Spielberger, C. D., Gorsuch, R. L., Lushene, R., Vagg, P. R. & Jacobs, G. A. (1983). Manual for the State-Trait Anxiety Inventor_y(Form Y ) .Palo Alto, CA : Consulting Psychologists Press. Stanovich, K. E. & West, R. F. (1979). Mechanisms of sentence context effects in reading: Automatic activation and conscious attention. Memory and Cognition, 7 , 77-85. Stanovich, K. E. & West, R. F. (1981). The effects of sentence context on ongoing word recognition: Tests of a two-process theory. Journal of Experimental Psychology :Human Perception and Performance, 7 , 658-672. Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18, 643-662. Watts, F. N., McKenna, F. P., Sharrock, R. & Trezise, L. (1986). Colour-naming of phobic-related words. British Journal of Psychology, 77, 97-1 08. Williams, J. M. G. & Broadbent, K. (1986). Distraction by emotional stimuli: Use of a Stroop task with suicide attempters. British Journal of Clinical Psychology, 25, 101-1 10. Williams, J. M. G. & Nulty, D. D. (1986). Construct accessibility, depression and the emotional Stroop task : Transient mood or stable structure? Personality and Individual Differences, 7 , 485-491. Williams, J. M. G., Watts, F. N., MacLeod, C. & Mathews, A. (1988). Cognitive Psychology and Emotional Disorders. Chichester : Wiley. Received 21 May 1990; revised version received 28 January 1992
Appendix A. Words used in studies AR
AMN
HR
HMN
Weak Worried Agony Panicky Failure Nervous Helpless Terrified Painful Die Sickness Disease Tragedy Accident Suffering Cancer Paralysed Despair Distressed Coffin
Take Bramble Verse Section Clothes Picture Interest Margarine Around CUP Material Library Whistle Instead Something Taller Expensive Service Understand Lesser
Optimistic Love Brave Successful Reassured Confident Strength Pleasure Happiness Ecstasy Healthy Homely Laughter Warmth Overjoyed Friend 1y Security Capable
Typewriter Ring Stick Profession Carpenter Cardboard Bu i1ding Magnetic Associate Grounds Climate System Inventor Corner Offspring Alphabet Para 11e1 Measure Cord Lighter
Good Relaxed
Note. AR = anxiety-related; AMN = anxiety-matched neutral; HR = happiness-related; HMN = happiness-matched neutral.
