Journal of Clinical and Experimental Neuropsychology

ISSN: 0168-8634 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/ncen19

Attentional deficits following closed-head injury Jennie Ponsford & Glynda Kinsella To cite this article: Jennie Ponsford & Glynda Kinsella (1992) Attentional deficits following closed-head injury, Journal of Clinical and Experimental Neuropsychology, 14:5, 822-838, DOI: 10.1080/01688639208402865 To link to this article: http://dx.doi.org/10.1080/01688639208402865

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Journal of Clinical and Experimental Neuropsychology 1992, Vol. 14, NO.5, p ~822-838 .

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Attentional Deficits Following Closed-Head Injury*

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Jennie Ponsford' and Glynda Kinsella2 Bethesda Hospital, Richmond, Victoria La Trobe University, Bundoora, Victoria

ABSTRACT Aimed to assess, in the light of current attentional theories, the nature of the attentional deficit in a group of severely traumatically head-injured subjects,relative to a group of orthopaedic rehabilitation patients, and to establish which neuropsychological measures best reflected the deficit. Three separate studies were conducted in order to meet these aims.The first study focused on selective attention; the second, on vigilance or sustained attention; the third, on the Supervisory Attentional System. Results provided no evidence for the presence of deficits of focused attention, sustained attention, or supervisory attentional control, but ample evidence for the presence of a deficit in speed of information processing. Those neuropsychological measures shown to be the best measures of this deficit included the Symbol Digit Modalities Test, simple and choice reaction-time tasks, colour naming and word reading scores on the Stroop, and the Paced Auditory Serial Addition Test.

A frequent complaint made by the victims of closed-head injury is that of their difficulty in concentrating. Recent follow-up studies covering periods from 3 months to 7 years postinjury (McKinlay, Brooks, Bond, Martinage, & Marshall, 1981; Oddy, Coughlan, Tyerman, & Jenkins, 1985; Van Zomeren & Van den Burg, 1985) have confirmed that poor concentration and slowness are amongst the more common problems reported by severely head-injured patients or their relatives. There has also been a growing body of evidence from neuropsychological studies, such as those of Gronwall and Sampson (1974), Miller (1970), Van Zomeren (1981), and Stuss et al. (1985), which suggests that attentional deficits may result from closed-head injury. However, the exact nature of these attentional deficits remains rather poorly understood, and many clinicians remain at a loss as to how to measure such difficulties objectively. There is a need to establish which neuropsychological measures are sensitive to attentional deficits in headinjured subjects.

* The authors wish to acknowledge the assistance of Carolyn Curran, Maria Nechwatal, Kim Ng, and Margaret Norden. Address for correspondence: Dr. Jennie Ponsford, Bethesda Hospital, 30 Erin Street, Richmond, Victoria, Australia, 3 121. Accepted for publication: February 12, 1992.

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INVESTIGATION OF ATTENTIONAL DEFICITS

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One possible reason for the relative lack of studies of attention following brain injury is the continuing controversy as to the meaning of the concept of attention and its mechanisms. Attention is clearly a multidimensional concept. Some of the aspects of attention that have emerged from recent theories include tonic and phasic alertness (the organism’s readiness to respond), sustained attention or vigilance (the organism’s capacity to sustain that readiness over periods from one-half to eight hours), and selective attention (the organism’s capacity to select out relevant information for conscious processing, and ignore irrelevant stimuli). According to the influential model proposed by Schneider and Shiffrin (19771, there are two forms of information processing: automatic and controlled. Automatic processing (involved in tasks such as driving a car) occurs without subject control, has no capacity limitations, and does not demand the subject’s conscious attention. Controlled processing, does, on the other hand, require conscious attention and has a limited capacity and rate. Schneider and Shiffrin (1977) used two measures of efficiency of performance on controlled processing tasks: speed of performance (or reaction-time) and accuracy. According to Schneider and Shiffrin’s (1977) model there are two qualitatively different limitations of selective attention. Errors of focused attention occur when automatic response tendencies interfere with a new task requiring controlled processing. Divided attention errors occur when the demands of a task exceed the subject’s conscious processing capacity or speed. Schneider and Shiffrin (1977) concluded that divided attention deficits result from limitations in the “rate of short-term search”; that is, in the rate of controlled information processing. Speed of information processing is, therefore, a central construct in divided attention. Shallice (1982) has subsequently put forward a more complex model, postulating the existence of a Supervisory Attentional System (SAS). This is said to regulate the efficient use of attentional resources in a goal-directed fashion, especially in novel or complex situations. This system was seen by Shallice to correlate with Luria’s (1966) unit for programming, regulation, and verification of activity. He predicted that its function was impaired by frontal-lobe injury. He and his colleagues went on to develop the Tower of London task as a test of the function of this system. Given that frontal-lobe contusion frequently results from closed-head injury, the present authors felt it would not be surprising to see impairment of this system in head-injured subjects. Following from the work of Van Zomeren, Brouwer, and Deelman (1984), who have made a significant contribution in this area, the present study aimed to assess aspects of attention in a group of severely traumatically head-injured subjects, and to establish which commonly used neuropsychological measures best reflected any deficits present. This would facilitate the assessment of attentional difficulties in clinical settings. Clearly, however, such neuropsychological measures may share more or less common variance. It is of importance, therefore, to determine if there is a minimum set of measures that, in linear combination, effectively discriminate between head-injured and normal subjects.

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Because of the large number of tasks that had to be administered to subjects, three separate studies were conducted in order to meet these aims. The first, and major, study focused on selective attention - specifically, the presence of deficits in focused attention and deficits in speed and/or accuracy of performance on tasks of increasing complexity. An attempt was made to examine phasic alertness within this study. The second study focused on vigilance, or sustained attention. The third study focused on the Supervisory Attentional System.

STUDY 1: SELECTIVE ATTENTION: FOCIJSED AND DIVIDED ATTENTION DEFICITS METHOD Subjects The experimental subjects for this study were 47 patients with severe closed-head injury of traumatic origin, who were admitted to Bethesda Hospital, Melbourne, for rehabilitation, and who met the criteria for entrance into the study. All subjects were aged between 16 and 45 years, had no history of previous neurological or psychiatric disturbance, were less than 12 months postinjury, and had sufficient visual acuity and dominant arm function to perform the set tasks. They had a period of posttraumatic amnesia (PTA) lasting at least 7 days, thereby being classified as severe head injuries according to Russell and Smith’s (1961) classification, and all subjects were judged to have emerged from PTA at least 2 weeks prior to the assessment. Whilst in PTA, the subjects had been monitored daily using the Westmead PTA Scale (Shores, Marosszeky, Sandanam, & Batchelor. 1986), and they were judged to have emerged from FTA when they received a perfect score on this scale on three consecutive days. Of the 47 head-injured subjects, 29 were males and 18 were females. Their ages ranged from 16 to 43 years (M= 23.4 years; SD = 7.4 years). The average interval between injury and assessment was 112.0 days (SD= 76.3 days), the range being 28 to 355 days. The subjects’ length of PTA ranged from 7 to 168 days (M= 39.6 days; SD = 34.8 days). Forty-two of the subjects had a PTA lasting more than 2 weeks. Glasgow Coma Scale (GCS) scores on admission to hospital were documented in 38 out of the 47 cases. The mean GCS score on admission to hospital for these 38 subjects was 4.7 (SD= 2.1). the range being 3 to 9. Of the 47 head-injured subjects. 42 had had CT scans following their injury. Of these 42 subjects, 5 showed no abnormality on CT, 22 showed bilateral pathology (6 of which showed edema only), and 15 showed unilateral pathology. Focal frontal lesions were specifically noted in the reports of 17 cases. However, it must be noted that CT scans have limited resolution, reducing their utility in localising damage resulting from closedhead injury. The subjects had an average of 11.4 years of education (SO= 2.1 years; range = 8 - 17 years). The control group consisted of 30 orthopaedically injured motor accident rehabilitation patients from Bethesda Hospital, matched for age and years of education with the headinjured group. They had no history of neurological or psychiatric disturbance, including drug or alcohol abuse, and had no documented history of head injury, loss of consciousness, or loss of memory surrounding their accident. They were also excluded if they were taking any medication that might potentially have affected their performance. They had to have a functional dominant arm in order to perform the tasks. The control group consisted of 24 males and 6 females. Their ages ranged from 16 to 42 years (M= 25.4 years; SD = 5.9 years). They had an average of 11.4 years of education (SD= 1.5 years; range = 9-16 years).

INVESTIGATIONOF ATI'ENlTONAL DEFICITS

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Measures and Procedures In general, an attempt was made to utilise commonly used neuropsychological measures in order to facilitate practical application of the findings of the present study by clinicians. Focused Attention Deficits The Stroop Color Word Test (Stroop, 1935) was used to assess the presence of focused attention deficits. The test consisted of three subtests: reading printed colour names, naming the colours of blocks, and naming the colours of words that are themselves colour names. The first two subtests are generally performed quickly and with ease, because they utilize essentially well-trained response tendencies, and no conflict is involved. However, on the third task, the subject must suppress the more automatic or well-trained tendency to read the word and name the colour instead, thereby requiring much more time for colour naming. The magnitude of the difference is an index of the interference effect. It was hypothesized that if head-injured subjects showed greater focused attention deficits, the interference effect would be significantly greater in the head-injured group than in the control group (that is, their scores would be disproportionately lower relative to the other two tasks). For each subtest, the score represented the number of words or colours correctly named in 45 seconds. The number of errors made on each subtest was also recorded. Divided attention: speed and accuracy of controlled information processing and effects of increasing load Schneider and Shiffrin (1977) used measures of speed of response and accuracy in their assessment of the efficiency of controlled information processing. They concluded that divided attention deficits result from limitations in the rate of controlled information processing. Divided attention deficits (in speed and/or accuracy) would become apparent with increasing load. Three central constructs in measuring the efficiency of divided attention are, therefore, speed of performance, accuracy of performance, and effects of increasing load or complexity. In the present study, a range of tasks was used to assess divided attention - which allowed for the measurement of speed of information processing and accuracy of performance at varying levels of complexity. Two of the tasks (Reaction time and the PASAT) enabled direct examination of the effects of increasing complexity or load on the task, a feature that is important in the examination of divided attention. i) Simple and Four-Choice Reaction time (Van Zomeren, 1981). These tasks were selected in order to assess and compare speed of reaction time as a measure of speed of information processing, in the two groups. Another aim was to assess the relative effects of increased task complexity on reaction time in each group. Thirdly, an attempt was made to examine the relative effects of a warning signal preceding the stimulus in head-injured versus control subjects, following from the work of Costa (1962), who found that the reaction time of brain-damaged subjects was not significantly lowered by the introduction of a warning signal as it is in normal subjects. It was felt that this might shed some light on the status of phasic alertness responses in this group of head-injured subjects. The apparatus was designed along the lines of that used by Van Zomeren (1981), enabling reaction-time to be split into a decision component and a movement component. The decision time, recorded in ms, was taken as the reaction-time measure, in order to avoid contaminating the reaction-time measure with the possible effects of subtle motor deficits. The apparatus was able to operate under four modes: Simple Reaction time with Warning Signal (a buzz preceded the stimulus by, on average, 1 s. but was randomly varied from 0.9-1.1 s in order to prevent anticipatory reactions), Simple Reaction time No Warning Signal, Choice Reaction time with Warning Signal, and Choice Reaction time N o Warning Signal.

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ii) Symbol Digit Modalities Test (Smith, 1973). Both written and oral forms were administered. The score for each form represented the number of items completed correctly. The number of errors made was also recorded.

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iii) Letter Cancellation Tusk. This was designed by the first author as a measure of speed of information processing. that also allowed for the measurement of accuracy of selective attention. One thousand capitalized letters of the alphabet were printed in a random order on an A-4 size page. The two target letters were B and M,and there were 50 of each of these letters distributed randomly on the page. The subject was asked to cross out all the B’s and all the M’s on the page as quickly as possible. The total time taken to complete the task was recorded, in seconds, as the speed measure. The accuracy measure was the percentage of target letters correctly crossed out. iv) Paced Auditory Serial Addition Test (PASAT) (Gronwall & Sampson, 1974). This was the final measure of speed of controlled information processing. A random series of taperecorded digits was presented to the subjects, who were instructed to add pairs of numbers, such that each number they heard was added to the one immediately preceding it. before the presentation of the next stimulus. The task was presented at four different pacings: with a 2.4 s, a 2.0 s, a 1.6 s, or a 1.2 s interstimulus interval. For each pacing, the percentage correct responses was computed, as were overall measures of the mean time per correct response (in seconds), and the error rate, as a percentage of the total number of responses across all pacings. RESULTS AND DISCUSSION Mean scores obtained by each group and univariate F ratios for each of the attentional variables are listed in Table 1. Looking first at focused attention, on the Stroop the head-injured group scored lower than the control group on each subtest, reflecting slower performances. They did not, however, show a disproportionately greater susceptibility to the interference effect on the third subtest, on which they were required to name the colours of words that were themselves colour names. A t test comparing the magnitude of the interference effect in the two groups indicated that the interference effect was, in fact, significantly greater in the control group than in the headinjured group ( t = 3.14, df = 75, p = .002). There was, therefore, no evidence to support the presence of greater focused attention deficits, as measured by the Stroop interference effect, in this group of head-injured subjects. There was, however, ample evidence of reduced speed of information processing in the head-injured group. As can be seen from Table 1, there were highly significant differences between the groups on all of the speed measures, the headinjured subjects performing consistently more slowly than the control subjects. On the other hand, whilst there was a tendency for the head-injured subjects to have slightly higher error scores on most of the measures, the error scores for both groups were low on most tasks. The only statistically significant differences in error scores between the head-injured and control groups occurred on the PASAT. Except on the PASAT, the head-injured subjects were performing more slowly, but not significantly less accurately than controls. The PASAT would

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Table 1. Mean Scores Obtained by Each Group and Univariate F-Ratios for Each of the Measures. ~~~

~

Head Injury (n= 47)

M

(SD)

62.2 (12.9) 1.1 (1.4)

73.7 0.4

(12.3) ( 1.4)

15.08 (1,751 .ooo*** '' .421 0.66

82.8 (17.3) 0.5 (0.9)

102.7 0.5

(15.5) (0.9)

26.35 (1,75) .000*** " .959 0.26

37.8 (11.0) 2.0 ( 1.5)

46.2 1.6

(10.0) ( 1.5)

11.45 1.31

(76.0) ( 1.9) (87.2) (0.2) (72.0) ( 1.9) (81.4) (0.9)

409.9 0.03 443.3 0.03 375.4 0.9 433.3 0.1

(60.4) (0.2) (54.3) (0.2) (38.6) ( 1.2) (47.8) (0.4)

21.89 (1,751 .000*** 0.58 .450 .000*** 41.93 ,841 0.41 .ooo*** 29.97 .loo 2.78 .ooo*** 37.6 .830 0.47

38.4 (12.1) 0.7 ( 1.3) 45.1 (13.7) 0.7 ( 1.2)

52.9 0.5 63.1 0.7

(11.4) (0.9) (11.1) ( 1.1)

27.57 0.39 36.37 0.67

448.7 (179.4) 88.7 (6.5)

304.7 90.2

(43.2) (4.9)

18.55 1.25

4.6 (1.6) 15.8 (11.1)

3.5 7.6

(1.1) (7.4)

11.36 7.34

.001***

64.7 62.5 55.3 39.8

(21.4) (16.6) (16.6) (12.7)

5.15 10.39 11.94 10.98

.026** ,002*** .001*** .001***

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(SD) STROOP word reading - score - errors colour naming - score - errors naming colors of words - score - errors SIMPLE RT-NWS (ms) - errors CHOICE RT-NWS (ms) - errors SIMPLE RT-WS ( m ~ ) - errors CHOICE RT-WS (rns) - errors SDMT -Written score - errors SDMT - Oral score - errors CANCELLATION - Time (s) - Percent correct PASAT Mean time per correct response Error rate Percent correct: 2.4 s pacing 2.0 s pacing 1.6 s pacing 1.2 s pacing

Control (n= 30)

486.9 0.3 558.7 0.04 453.8 1.6 534.0 0.2

54.8 49.7 43.1 30.3

(16.8) (17.2) (14.1) (12.0)

F

df

" "

P

.001*** .257

.000*** ,536

,ooo*** .979

.ooo*** .267

.008**

appear to b e the most complex of the four tasks, making significantly greater cognitive demands. Unlike the other tasks, it was not paced by the subject. The head-injured subjects were, therefore, unable to sacrifice speed of performance to achieve greater accuracy which may be what they did on the less cognitively demanding tasks.

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From the results of the reaction-time task, it can be seen that, whilst both simple and four-choice reaction-time tasks discriminated significantly between the groups, the magnitude of the difference between groups was significantly greater on the choice reaction-time tasks, both with and without a warning signal. A series of t tests comparing the magnitude of the relative differences in reaction-time between simple and four-choice reaction-time tasks confirmed that the head-injured subjects were disproportionately slower than controls on the choice reaction-time tasks, both with and without a warning signal (Reaction-time No Warning Signal: t = 4.77,df= 75,p= .OOQ Reaction time Warning Signal: c = 1.18, df = 71, p = .032).It appears that the reaction times of the head-injured subjects were disproportionately affected by the increased complexity of the task. On the PASAT, however, there was no disproportionate deterioration in performance of the head-injured subjects with increased rate of presentation of the digits. Whilst the head-injured subjects performed consistently and significantly worse than controls across all pacings, the results of an analysis of variance showed no significant interaction between group and pacing ( F = .61, d ? =3,225, p = .610). It was somewhat surprising that a greater complexity effect was evident in the head-injured subjects on the Reaction time Task but not on the PASAT. The PASAT would appear to be a far more complex task at all levels, demanding far greater cognitive effort. Possible reasons for these differential effects require further investigation. The introduction of a warning signal on the reaction-time task reduced the reaction-times of both groups to an approximately equal degree on both simple and choice reaction time tasks. Results of t tests comparing the magnitude of reduction in reaction-time in response to a warning signal confirmed that there were no significant differences between the groups in this respect for either simple or choice reaction-time tasks (Simple RT: t = -.11, d ! = 7 5 , p = .91; Choice RT: t = 1.57, df= 75,p = .120).Thus, in this group of head-injured subjects, there was no evidence to support the presence of abnormal phasic alertness responses, as measured by speed of response to a warning signal. Whilst a large number of measures individually discriminated between the groups, there may have been common factors underlying the attentional deficits shown by head-injured subjects on these variables. That this might be the case was indicated by the substantialcorrelationsshown between some of these variables. For example, performance on the written version of the Symbol Digit Modalities Test correlated 0.881 with performance on the oral version of the same test, performance on the color naming subtest of the Stroop correlated 0.749 with performance on the word reading subtest, and performance on the 1 6 s pacing on the PASAT correlated 0.872 with performance on the 1.2-spacing. The extent to which common variance may account for some of the differences between the groups on the individual measures was best determined by a stepwise discriminant function analysis. The results of Step-up Discriminant Function Analysis are presented in Table

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Table 2. Best Set of Discriminating Variables, Their Correlations With the Canonical Discriminant Function and Canonical Discriminant Function Coefficients. POOLED STANDARDIZED WITHIN-GROUPS CANONICAL CORRELATIONS DISCRIMINANT BETWEEN FUNCTION DISCRIMINATING COEFFICIENTS VARIABLES AND CANONICAL DISCRIMINANT FUNCTION

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VARIABLE

CHOICE Reaction-time - NO WARNING SIGNAL SYMBOL DIGIT MODALITIES TEST - ORAL SIMPLE Reaction time - WITH WARNING SIGNAL SIMPLE Reaction time - NO WARNING SIGNAL STROOP WORD READING SCORE PASAT - PERCENT CORRECT FOR 1.6 S PACING PASAT - PERCENT CORRECT FOR 2.0 S PACING STROOP -NAMING COLOURS OF WORDS STROOP WORD READING SUBTEST -ERROR SCORE

.62359 .58078 .52721 .45060 -.37397 -.33274 -.31044 -.32592 .07798

1.34600 -.79209 .65231 -1.13187 .725 16 -.76600 .81142 -.35826 .23314

2. The criterion for variable selection was Wilks’ lambda, the F to enter and remove was set at 1.00, the tolerance level for variable entry equalled .001, and the prior probability for classification into each group was 0.50. Box’s M test revealed homogeneity of variance [ F (45,12687.7) = 1.29, p = .0931]. Table 2 lists the correlations between each of the variables and the canonical discriminant function. The discriminant function consisted of 9 variables that in a weighted sum, provided the best discrimination between the groups. The function discriminated significantly at p = .001, with Wilks’ lambda = .410, Chi square = 62.82, df = 9. Table 3 shows the classification results indicating how well the final set of discriminating variables discriminated between the groups. The set of variables correctly classified 88.31 percent of grouped cases. That factorial commonality underlay the discrimination value of some of the individual variables was apparent. Thus, for example, Choice Reaction-time With Warning Signal showed the second highest correlation with the discriminant

Table 3. Classification Results. Actual Group

Number of Cases

1. Head Injury 2. Control

47

30

Predicted Group Membership 1. Head Injury 2. Control

38 (80.9%) 0 (0.0%)

9 (19.1%) 30 (100.0%)

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JENNIE PONSEORD AND GLYNDA IUNSEJ-LA

function but did not appear as a selected variable in the discriminant analysis. It correlated 0.912 with Choice Reaction-time No Warning Signal and -.481 with Symbol Digit Modalities Test-Oral Version. These two variables, that also correlated highly with the discriminant function were selected in the discriminant analysis. The discriminant function established with step-up discriminant analysis is always constrained by the single best discriminating variable, however small the difference may be between this and the other variables. The search for the best discriminating function is ideally achieved with a step-down analysis. No algorithm for a step-down discriminant function analysis is available. However, a step-down regression analysis with groups as the criterion variable may give some indication of the subset of variables that may be involved. This analysis yielded a regression equation involving only one of the attentional measures, the oral version of the Symbol Digit Modalities Test, with a Multiple R of 0.60 (F = 41.14, df= 1,75, p< .OOOO). This result suggests that the bulk of the betweengroups variance accounted for by the discriminant function may be attributed to this variable. This was confirmed with a subsequentdiscriminant function analysis, using only this variable (Wilks’ lambda = .67343, Chi-square = 29.5, df= 1, p< .OOOO) and 76.6 percent correct classification. The increase in classification errors compared with the nine-variable function was minimal. These results suggest that divided attention deficits in the head-injured subjects may be vested primarily in the oral version of the Symbol Digit Modalities Test. With discriminant and regressional analysis, shrinkage is always a problem and cross-validation of these findings is necessary before any firm conclusions C a n be drawn. However, the subject-to-variable ratio for both the nine-variable and the single-variable function was sufficiently high to suggest that shrinkage may not be substantial (Fletcher, Rice, & Ray, 1978). In summary, as far as selective attention was concerned, there was no evidence from this study to support the presence of increased focused attention deficits. There was, however, ample evidence for the presence of reduced speed of information processing in severely head-injured subjects. Results suggested that, where possible, head-injured subjects tended to sacrifice speed to maintain accuracy. Where this was not possible, as on the PASAT, they made significantly more errors than controls. There was evidence of a differential effect of increasing load or complexity in the head-injured subjects’ performance on the reactiontime task. However, no complexity effect was apparent on the PASAT. The test that was shown to be the best single measure of the deficit in speed of information processing was the oral version of the Symbol Digit Modalities Test. However, simple and choice reaction-time tasks, colour naming and word reading scores on the Stroop, and the Paced Auditory Serial Addition Test were also good discriminators. Having established the presence of this deficit in speed of information processing, the next step was to examine the capacity of a second group of subjects in sustained attention or vigilance.

INVESTIGATION OF AlTENTIONALDEFICITS

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STUDY 2: VISUAL VIGILANCE

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METHOD Subjects The experimental subjects for this study were 19 patients (14 males, 5 females) with severe closed-head injury of traumatic origin, who were admitted to Bethesda Hospital for rehabilitation, and who met the criteria for entrance into the study (the same as in Study 1). Their ages ranged from 16 to 41 years (M= 26.1 years; SD = 8.0 years). The average interval from injury to assessment was 75.4days (SD= 34.1 days), the range being 28-153 days. The subjects’ mean length of PTA was 32.0 days (SD= 25.5 days), the range being 7-90 days. Glasgow Coma Scale scores on admission to hospital were available for 14 of the 20 subjects. For these 14 subjects, the mean GCS score on admission to hospital was 4.8 (SD= 2.1), the range being 3 to 9. Eighteen of the 19 head-injured subjects had had CT scans following injury. Of these, the scans of three subjects showed no abnormality. Seven subjects showed bilateral pathology and eight showed unilateral pathology. Seven of these subjects were reported to have focal frontal-lobe lesions. The subjects had an average of 11.6 years of education (SD= 1.8 years; range = 9-16 years). The control group consisted of 20 orthopaedically injured motor accident rehabilitation patients from Bethesda Hospital, matched for age and years of education with the headinjured group. They were selected according to the same criteria used for selecting controls in Study 1. The control group consisted of 17 males and 3 females ranging in age from 17 to 45 years (M= 25.6 years SD = 8.1 years). They had an average of 11.3 years of education (SD = 1.8 years; range 9-14 years).

Apparatus and Procedures Visual Vigilance Tusk. This task was designed along the lines of that used by Anderson, Halcomb, and Doyle (1973) to assess visual vigilance in leaming-disabled children. For this task, the subject was seated alone in a quiet room at a table, on which was mounted the same tilted metal box used for the reaction-time tasks in Study 1. Two pairs of lights were mounted at the top of the apparatus. One of each of the lights flashed in combinations of red-red, green-green, red-green, or green-red at a high event rate of one flash every 2 s, or 30 per minute. The stimulus-duration was 0.2 s. A 2-minute practice session preceded the task, which then lasted for about 45 minutes (since the task was subject-paced, the exact length of time taken to complete the task was determined by the reaction-times of the subject). A total of 900 stimuli were presented, of which 60 were either red-green or green-red combinations. These 60 stimuli were the target stimuli. They occurred randomly, with the restriction that 10 targets occurred in each block of 150 stimuli. The subject held hisher finger at a resting point while waiting for a signal, and was instructed to press the right-hand response button, marked True, whenever target stimuli appeared, and to press the left-hand response button, marked False, whenever any other stimulus appeared. The task was thereby paced by the subject. Correct button presses to target stimuli were designated hits. Incorrect responses when target stimuli occurred were designated misses, and incorrect responses when nontargets occurred were designated fulse positive responses. The time between the offset of the signal and the onset of button pressing constituted the measure of reaction-time, recorded in milliseconds. For each subject, the total number of hits, misses, and false positives, and their mean reaction-times, in ms, were computed for the whole task, and for six consecutive segments of 150 stimuli. Each of the control and head-injured subjects performed the vigilance task once.

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RESULTS AND DISCUSSION Figure 1 shows the number of hits made by the two groups over each of the successive time periods. It can be seen that, in terms of number of hits, the performance of both groups tended to deteriorate in the third and fourth time period (that is, between 15 and 30 min after commencing the task) but improved again somewhat in the fifth and sixth time period. Results of a two-way analysis of variance showed that the main effect of Time-on-Task was significant at the .005level (F = 3.48; df= 5,185; p = .005).This implied that the test was capable of eliciting impairments of sustained attention. However, there was no evidence for a differential effect of Time-on-Task on Groups (Time-on-Task x Groups interaction: F = 1.77; df = 5,185; p = .122). The performance of the head-injured subjects did not deteriorate significantly more over time than did that of the control group. The head-injured group tended to make fewer hits, on average, but the results of the analysis of variance indicated that the differences between groups were not significant (F= 1.37; df= 1,37;p = .250). Similarly, there were no significant differences in the number of false positive responses made by each group (F = .06; df= 1,37; p = .803), both groups making very few false positive responses overall (see Figure 2).

II

I

I

0

1

2

I

I

i

I

3

4

5

0

TIME PERIOD

* Head Injury * Control Fig. 1. Percentage hits made by each group over the six successive time periods.

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NUMBER OF FALSE POSITIVES

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0.6

0

1

2

3

5

4

6

TIME PERIOD

*Head Injury

-+-

Control

Fig. 2. Mean number of false positive responses made by each group over the six successive time periods.

Figure 3 shows the mean overall reaction-times of the two groups over each of the six successive time periods and the reaction-times to target stimuli. The head-injured group was significantly slower to respond than was the control group across the entire task ( F = 12.58; df= 1,37;p = .OOl). There was, however, no significant interaction between Groups and Time-on-Task ( F = 0.98; df= 5,185; p = .429), indicating that there was no differential effect of Time-on-Task between the groups in terms of reaction-time. In both groups, reaction-times to target stimuli were much slower than were reaction-times to nontarget stimuli. Again, the head-injured group was significantly slower to respond than were the controls to target stimuli across the entire task ( F = 21.68; df= 1,37; p = .OOO). There was no significant interaction between Groups and Time-on-Task ( F = 1.29; df= 5,185; p = .271). In summary, the head-injured group performed significantly slower on this task than did the control group. As in the previous study, they did not, however, perform significantly less accurately. Most importantly, there were no statistically significant differences between the groups in terms of their responses over time. The performance of head-injured subjects did not deteriorate over time significantly more than did that of the control subjects.

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1100

8oo 700

600

500 400

ENNlE PONSFORD AND GLYNDA KINSELLA

REACTION TIME (ms) I

14

F

0

+ ,

A Y

1 ++ 4

u

HI R.T to targets

A

0

-5 CON R.T to targets

-63-

-st HI Overall R.T

1

"

n -

I

I

2

3

CON Overall R.T

4

5

6

TIME PERIOD Fig. 3. Mean overall reaction-times and reaction-times to targets only for each group over the six successive time periods.

STUDY 3: SUPERVISORY ATTENTIONAL CONTROL

METHOD Subjects The experimental subjects for this study were 22 patients (15 males, 7 females) with severe closed-head injury of traumatic origin, who were admitted to Bethesda Hospital for rehabilitation, and who met the criteria for entrance into the study (the same as those for Studies 1 and 2). Their ages ranged from 16 to 43 years (M = 26.0 years; SD = 8.8 years). The average interval between injury and assessment was 85.1 days (SD= 47.0 days), the range being 28 - 201 days. The subjects' length of FTA ranged from 7 days to 90 days (M = 33.2 days; SD = 25.6 days). The Glasgow Coma Scale scores on admission to hospital were available for 16 of the 22 subjects. These 16 subjects had a mean GCS score of 4.88 (SD= 2.23), the range being 3 to 9. Twenty-one of the 22 head-injured subjects had had CT scans following injury. Three cases showed no abnormality. Nine cases showed bilateral pathology (of which one showed edema only), and nine cases showed unilateral pathology. Eight cases were specifically noted to have focal frontal-lobe lesions. The subjects had an average of 11.4 years of education (SD= 1.8 years; range = 9 - 16 years). The control group consisted of 19 orthopaedicallyinjured motor accident rehabilitation patients from Bethesda Hospital (18 males); they were matched for age and years of education with the head-injured group, and selected according to themme criteria used to select controls in Studies 1 and 2. Their ages ranged from 17 to 45 years (M = 25.3 years; SD = 8.0 years). They had an average of 11.4 years of education (SO = 2.0 years; range = 9-16 years).

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INVESTIGATION OF ATTENTIONAL DEFICITS

Apparatus and Procedures Following from the work of Shallice (1982), the Tower of London task was used to investigate the relative capacities of the two groups of subjects in terms of their so-called Supervisory Attentional Control - their capacity to plan the solution to complex and novel tasks, allocating controlled attentional resources in a goal-directed fashion. The Tower of London task was constructed so that satisfactory performance would require the use of a general programming system, such as the Supervisory Attentional System. The apparatus consisted of three beads (one red, one green, and one blue) which had to be moved from a starting configuration on three sticks of unequal length to a target position in a minimum number of moves and according to certain rules. Four problems required a minimum of two or three moves, four required four moves, and four required five moves. If the subject made a mistake or broke the rules, the stopwatch was turned off, the beads returned to the starting pattern, and the subject was asked to try again. They were allowed as many attempts as required to solve the problem, up to a maximum time limit of 60 s. Four measures were recorded. The planning time represented the interval, in seconds, from the experimenter’s last verbalization to the f i s t “click” of the apparatus, which occurred when the subject began to move the beads in an attempt to solve the problem. The mean planning time was calculated across the 12 problems. The solution time represented the time, in seconds, from the experimenter’s last verbalization until the subject had successfully solved the problem or until the time limit had expired. The mean solution time was also calculated across the 12 problems. The number of errors made was also recorded, as was the total number of correct solutions achieved within the time limit.

RESULTS AND DISCUSSION Table 4 shows the results obtained by the two groups on the Tower of London task. Consistent with the results of the two previous studies, the head-injured subjects had significantly longer planning times and solution times than did the control subjects. There was also a significant difference in the number of problems solved correctly within the time limit. There were, however, no significant differences between the groups in terms of the number of errors made. Once again, the pattern of reduced speed of information processing, but comparable accuracy, was apparent in the head-injured subjects.

Table 4. Results Obtained by the Head-Injured and Control Groups on the Tower of London Task. Head-injured ( n = 22) Mean Planning Time (s) Mean Solution Time (s) Error Score Number Correct

M

(SD)

6.7 23.0 5.8 10.6

(3.5) (6.0) (2.8) (1.0)

Control

t

(n = 19)

M

(SD)

4.0 16.0 6.4 11.4

(2.5) (4.0) (2.9) (0.8)

2.84 4.26 -0.72 -2.75

df

39 39 39 39

P

.007** .OOO** ,473 .009**

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JENNIE PONSFORD AND GLYNDA KINSELLA

-

30 20

-#+Head

10 -

0

I

I

Injury

1

4-Control I

I

I

Fig. 4. Mean number of problems solved by each group at the f i t attempt in less than 60

seconds.

The mean number of problems solved at the first attempt in less than 60 s by each group of subjects is shown in Figure 4. It can be seen from this that there were no significant differences between the groups in this respect; if anything, the head-injured group performed slightly better than the control group on the more difficult problems. In this respect, the performance of this head-injured group differed from that of Shallice's (1982) group of patients with left-anterior lesions. They performed significantly worse than other groups in terms of percentage of problems solved correctly at the first attempt, having particular difficulty with the more complex problems. They achieved an average of less than 45 percent for problems requiring four moves, and less than 30 percent for problems requiring five moves. Our group of head-injured subjects did not exhibit impairment of the so-called Supervisory Attentional System described by Shallice (1982), as measured by performance on the Tower of London task. There was, however, further evidence of reduced speed of information processing in the head-injured group.

CONCLUSIONS The results of these studies, taken together, provide no evidence for the presence of deficits in focused attention, sustained attention, or Supervisory Attentional

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INVESTIGATION OF ATTENITONAL DEFICITS

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Control in severely head-injured subjects. There was, however, ample evidence for the presence of reduced speed of information processing in the head-injured group. The test that was shown to be the best single measure of this deficit was the oral version of the Symbol Digit Modalities Test, although simple and choice reaction-time tasks, colour naming,and word reading scores on the Stroop, and the Paced Auditory Serial Addition Test were also good discriminators. Results suggested that, where possible, head-injured subjects tended to sacrifice speed to maintain accuracy, but where this was not possible, as on the PASAT, they made significantly more errors than did controls. There was evidence of a differential effect of increasing complexity of task in the head-injured subjects’ performance on the reaction-time task, but not on the PASAT. These results are somewhat contradictoryto widely held assumptionsregarding the attentional deficits of traumatically head-injured patients: namely, that headinjured patients not only perform more slowly, but that they also make more attentional errors, have difficulty in sustaining attention, and show poor selfregulation of their attentional resources. The results of the present studies are, however, entirely consistent with the findings of some previous research in this area, including that of Gronwall and Sampson (1974), Miller (1970), Van Zomeren (1981), Brouwer and van Wolfelaar (1985), and Stuss et al. (1985), who have consistently found reduced speed of performance, but not significant reductions in terms of accuracy or performance over time, relative to controls. Whilst it may be that the tasks used to assess attention in the present study were not sensitive enough, it is clear that caution should be exercised in interpreting the neuropsychological test performances of head-injured patients, being careful to separate out speed of performance from quality of performance. Finally, the results of the present study suggest that it may be possible to achieve a greater quality of performance from head-injured subjects by slowing down the pace at which information is presented, reducing background distractions or noise, or allowing additional time to complete tasks.

REFERENCES Anderson, R.P., Halcomb, C.G., & Doyle, R.B. (1973). The measurement of attentional deficits. Exceptional Children, 39, 534-539. Brouwer, W.H., & van Wolfelaar, P.C. (1985). Sustained attention and sustained effort after closed-head injury: Detection and 0.10 Hz heart rate variability in a low event rate vigilance task. Cortex, 21, 1 1 1-1 19. Costa, L.D. (1962). Visual reaction-time of patients with cerebral disease as a function of length and constancy of preparatory interval. Perceptual and Motor Skills, 14, 391. Fletcher, J.M., Rice, W.J., & Ray, R.M. (1978). Linear discriminant function analysis in neuropsychological research: Some uses and abuses. Cortex, 14,564-577. Gronwall, D.M.A., & Sampson, H. (1974). The psychological effects of concussion. Auckland: Auckland University Press. Luria, A.R. (1 966). Higher cortical function in man. London: Tavistock. McKinlay, W.W., Brooks, D.N., Bond,M.R.,Martinage, D.P., tkMarshal1,M.M. (1981).

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The short-term outcome of severe blunt head injury as reported by relatives of the injured persons. Journal of Neurology, Neurosurgery and Psychiatry, 44,527. Miller, E. (1970). Simple and choice reaction-time following severe head injury. Cortex,

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6, 121-127.

Oddy, M., Coughlan, T., Tyerman, A., & Jenkins, D. (1985). Social adjustment after closed-head injury: A further follow-up seven years after injury. Journal of Neurology, Neurosurgery and Psychiatry, 48,564-568. Russell, W.R., & Smith, A. (1961). Posttraumatic amnesia in closed head injury. Archives of Neurology. 5,4. Schneider, W., & Shiffrin, R.M.(1977). Controlled and automatic human information processing: I. Detection, search and attention. Psychologicai Review, 84.1-66. Shallice, T.(1982). Specific impairments of planning. In D.E. Broadbent & L.Weiskrantz (Eds.), The neuropsychology of cognitive function (pp. 199-209). London: The Royal Society. Shores, E.A., Marosszeky, J.E., Sandanam, J., & Batchelor, J. (1986). F'reliminary validation of a clinical scale for measuring the duration of posttraumatic amnesia. Medical Journal of Australia, 144.569-572. Smith, A. (1973). Symbol Digit Modalities Test. Los Angeles: Western Psychological Services. Stroop, J.R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18,643-662. Stuss, D.T.. Ely, P., Hugenholtz, H., Richard, M.T., La Rochelle, S.,Poirier, C.A., & Bell, I. (1985). Subtle neuropsychological deficits in patients with good recovery after closed-head injury. Neurosurgery, 17,4147. Van Zomeren, A.H. (198 1). Reaction-timeand attentionafer closed head injury. Lhg: Swets & Zeitlinger. Van Zorneren, A.H., Brouwer, W.H., & Deelrnan, B.G.(1984). Attentional deficits: The riddles of selectivity. speed and alertness. In N. Brooks (Ed.), Closed-head injury: Psychological, social and family consequences (pp. 74-107). Oxford: Oxford University Press. Van Zomeren, A.H., & Van Den Burg, W.(1985). Residual complaints of patients two years after severe head injury. Journal of Neurology, Neurosurgery and Psychiatry, 48, 21-28.

Attentional deficits following closed-head injury.

Aimed to assess, in the light of current attentional theories, the nature of the attentional deficit in a group of severely traumatically head-injured...
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