Acta Psychologica 148 (2014) 173–180

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Time perception and temporal order memory Scott W. Brown 1, G. Andrew Smith-Petersen Department of Psychology, University of Southern Maine, Portland, ME 04104–9300, United States

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Article history: Received 15 November 2013 Received in revised form 4 February 2014 Accepted 11 February 2014 Available online 4 March 2014 PsycINFO classification: 2340 2343 2346 Keywords: Time perception Temporal order Attentional resources Dual-task interference

a b s t r a c t The purpose of this research was to investigate the relation between the attentional resources underlying time perception and temporal order memory. Subjects made judgments about temporal attributes associated with a series of wordlists. Each word was displayed for 1.4 s, and the lists contained 10 words (14 s total), 15 words (21 s total), or 20 words (28 s total). Subjects judged either the list duration, the temporal order of the words, or both duration and temporal order. In addition, there were three mental workload conditions: control (no additional task requirements), and two mental arithmetic tasks (subtract 3 or subtract 7 from a series of random numbers). The results showed a pattern of bidirectional interference between timing and temporal order: the concurrent temporal order task interfered with duration judgments, and the concurrent timing task interfered with temporal order judgments. Bidirectional interference also occurred between the mental workload task and both duration judgments and temporal order judgments. The results indicate that duration and temporal order are closely related temporal attributes, and suggest that the processing of these attributes relies on a common set of executive attentional resources. © 2014 Elsevier B.V. All rights reserved.

“Temporal judgments require an ordered memory representation of the event sequence under concern and this requires at least a partial retrieval of the order of the constituent events” (Michon & Jackson, 1984, p. 303). 1. Introduction This research concerns the nature of temporal information. Our interest centers on the relationship between perceived duration and temporal order memory (also known as serial order memory). Are judgments of duration and judgments of temporal order essentially equivalent in some sense, or are they different? Conceptually, it seems appropriate to place various temporal attributes together into the same general category. Attributes such as duration (the temporal extent of an interval), order (the sequencing of a series of events), successiveness and simultaneity (the temporal relation between two or more events), and change (as indicated by a shifting or transformation of stimulus events) all involve temporal information processing. An especially close connection would seem to exist between duration and order or sequence processing (Brown & Merchant, 2007). Monitoring the duration of events typically involves segmenting an interval into an ordered series of smaller units, as in generating counts or rhythmic sequences (Grondin, Meilleur-Wells, & Lachance, 1999; Grondin, Ouellet, & Roussel, 2004; Guay & Wilberg, 1983; Poynter, 1989; Poynter & Homa, 1983). Similarly, ordering a sequence may involve

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http://dx.doi.org/10.1016/j.actpsy.2014.02.003 0001-6918/© 2014 Elsevier B.V. All rights reserved.

establishing explicit temporal relations between the component events, an operation that relies fundamentally on timing processes. Many theoretical accounts of serial order memory emphasize the role of timing processes, postulating that item order is represented by placing the items along a temporal dimension (e.g., Brown, Morin, & Lewandowsky, 2006; Brown, Preece, & Hulme, 2000; Farrell & McLaughlin, 2007; Lewandowsky, Brown, Wright, & Nimmo, 2006; Lewandowsky, Nimmo, & Brown, 2008). It follows that the perception of these temporal attributes would share common cognitive mechanisms or processes. We approach this topic by focusing on the role of attentional resources in temporal processing. If duration and order are closely related attributes, then one may expect that manipulations of attentional processing would produce comparable effects both in duration judgments and in temporal order judgments. One basic issue is whether a pattern of bidirectional (i.e., mutual) interference occurs when duration and ordering tasks are performed together, which would imply that both tasks rely on the same set of attentional resources. In the sections that follow, we review the research bearing on these issues.

1.1. Relation between duration and order processing Research on the relation between duration and order is limited. Although there exists a well-established literature on duration judgments and a substantial body of work on temporal order judgments, research in these different areas has tended to develop independently. However, a small number of studies employing diverse methodologies have

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examined the relationship between these temporal attributes, and this research points to a close connection between duration and order. In one experiment (Elvevag, Brown, McCormack, Vousden, & Goldberg, 2004), schizophrenic patients and control subjects performed a line length judgment task, a timing task in which they judged the duration of a series of 333 to 2333 ms tones, and a temporal order task in which they judged the position of a probe letter within a 7-letter sequence. The results showed that both groups were equally accurate at judging line lengths, but the patients were less accurate than the controls in their judgments of duration and temporal order. Elvevag et al. (2004) argued that duration and order tasks rely on temporal processing resources, and that the poor performance of the patients on these tasks supports a temporal deficit hypothesis of schizophrenia. Farrell (2008, exp.1) examined the relation between memory for order and rhythm timing. Lists of 6 digits were presented with irregular intervals separating the digits. Some trials included grouping instructions in which subjects were asked to perceive the 6 digits as being composed of two groups of 3 digits each. Following list presentation, a cue prompted subjects to either recall the digits in order or tap on a button to reproduce the rhythm of the digit sequence. The results showed that grouped lists lead to more accurate serial recall and more accurate rhythm reproduction, leading Farrell (2008) to conclude that there was a “common basis for timing and order information in short-term memory” (p. 136). Brown, Vousden, and McCormack (2009) devised a series of experiments to examine the relation between (a) recalling the serial order of items as a function of their temporal distance from the time of recall, and (b) judging the same temporal distance intervals in a duration discrimination task. Overall, serial position curves on the memory tasks paralleled serial position curves on the duration discrimination tasks. For example, in one study (exp. 1) 7 letters were presented sequentially followed by a probe letter; the task was to judge the serial position of the probe. The results showed a strong recency effect (memory of the last 4 items) and a smaller primacy effect (memory of the first 3 items). This pattern was duplicated in a timing task (exp. 2), in which subjects judged the durations of 7 tones (ranging from 333 to 2333 ms) that represented the temporal distances of the items in the previous experiment. Timing performance was most accurate for the shorter intervals (corresponding recency in exp. 1) and next most accurate for the longer intervals (corresponding to primacy). These results support the idea that timing is an important component of memory for serial order. 1.2. Effects of mental workload on duration and order processing Mental workload refers to the amount of mental effort or attentional resources needed to perform a task (O'Donnell & Eggemeier, 1986). In the duration judgment literature, mental workload has been used to demonstrate what is known as the interference effect. The interference effect refers to a disruption in timing that occurs when subjects are asked to keep track of time and perform a concurrent distractor task during the interval (for summaries of this work, see Block, Hancock, & Zakay, 2010; Brown, 1997, 2008, 2010). Compared with control conditions without any concurrent task, dual-task conditions typically lead to greater error in duration judgments. This error in timing may be in the form of underestimation error, absolute error, or increased variability in duration judgment responses. Many theorists (e.g., Brown & West, 1990; Hicks, Miller, Gaes, & Bierman, 1977; Zakay, 1989) attribute the interference effect to a diversion of attentional resources away from temporal processing. This view is supported by studies employing various techniques designed to manipulate attentiveness to the passage of time. In general, the less attention directed to time, the greater the error in duration judgments (Brown, 2008). All this research establishes time perception as an attentional task that is very sensitive to resource allocation. There is also evidence for a similar interference effect occurring with temporal order judgments. This work bears on a debate as to whether temporal order information is automatically encoded or whether it

requires intentional, controlled processing. Initially, theorists had proposed that the order information contained in a sequence of items was extracted automatically when that sequence was processed (Hasher & Zacks, 1979). This encoding was thought to be automatic and unintentional, using few (if any) attentional resources. However, a number of subsequent empirical studies have contradicted this notion (Auday, Kelminson, & Cross, 1991; Jackson, 1985; Jackson & Michon, 1984; Marshall, Chen, & Jeter, 1989; Michon & Jackson, 1984; Tzeng, Lee, & Wetzel, 1979; Zacks, Hasher, Alba, Sanft, & Rose, 1984). This research shows that encoding temporal order information is a deliberative, capacity-consuming process. For example, there is an effect of intention. Temporal order judgments are more accurate when subjects are instructed to pay attention to the ordering of the event sequence (e.g., Naveh-Benjamin, 1990a, 1990b). In one experiment (Correa, Sanabria, Spence, Tudela, & Lupianez, 2006), subjects judged the temporal order of two lights whose onsets were separated by 10 to 110 ms. A cue indicating whether the lights would appear sooner (400 ms) or later (1400 ms) in the following interval directed subject's attention to different parts of the interval. The results showed that valid cues lead to more accurate judgments and smaller JNDs (Just Noticeable Differences) relative to invalid cues. These effects are analogous to comparisons of prospective (intentional) versus retrospective (incidental) duration judgments, which show that prospective judgments are generally longer and more accurate than retrospective judgments (Block & Zakay, 1997). A critical finding is that concurrent distractor tasks such as shadowing (Healy, 1975, 1977), articulatory suppression (Alloway, Kerr, & Langheinrich, 2010; Crowder, 1978; Jones, Farrand, Stuart, & Morris, 1995), and manual tapping (Alloway et al., 2010) act to disrupt temporal order memory. Naveh-Benjamin (1990a, exp. 2) had subjects attend to the temporal order of words in a list and perform a concurrent arithmetic task. The results showed that the more demanding the arithmetic task, the greater the impairment in temporal order judgments. Attentional allocation is an explicit element in some contemporary theories of temporal order memory. The computational model known as SIMPLE conceives of memory items represented in a multidimensional space, with one dimension representing time (Brown, Neath, & Chater, 2007; Lewandowsky et al., 2006). SIMPLE includes a parameter representing the “attentional weight” given to the temporal dimension. As more attention is devoted to time, there is a corresponding reduction in the amount of attention devoted to other dimensions, and vice versa. Thus, workload studies of both perceived duration and temporal order memory produce similar results. Both types of tasks are resourcedependent, are sensitive to resource allocation, and are susceptible to interference from concurrent distractor tasks. 1.3. Bidirectional interference in duration and order processing The interfering effect of concurrent distractor tasks is an important issue in the time perception literature. Resource theory (Navon & Gopher, 1979, 1980; Wickens, 1984) posits that if two tasks rely upon the same pool of attentional resources, then the simultaneous performance of both tasks should suffer (producing a pattern of bidirectional interference) due to resource competition. In contrast, if the two tasks rely on different resource pools, or if the resource overlap between them is only partial, then interference is expected to be either nonexistent or unidirectional, with one task showing interference but the other task being unaffected (e.g., Navon & Gopher, 1980; Tsang, Shaner, & Vidulich, 1995; Wickens, 1980). Therefore, interference patterns between concurrent timing and distractor tasks may reveal the nature of the attentional resources that support duration processing (Brown, 2008). Distractor tasks involving executive cognitive functions tend to produce bidirectional interference patterns with timing, whereas nonexecutive distractor tasks produce unidirectional interference (that is, they interfere with timing, but timing does not interfere with them); see Brown (2006) for a review. Executive functions are cognitive

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processes that monitor and control thought and behavior (Logan, 1985; Stuss & Alexander, 2000). Such processes include planning, reasoning, memory updating, attentional switching, and inhibitory control (Baddeley, 1986; Baddeley & Della Sala, 1996; Banich, 2009; Royall & Mahurin, 1996). Although some studies have failed to find a relation between timing and executive function (e.g., Fortin, Schweickert, Gaudreault, & Viau-Quesnel, 2010; Ogden, Salominaite, Jones, Fisk, & Montgomery, 2011), recent research by Brown, Collier, and Night (2013) found strong bidirectional interference effects between timing and shifting, updating, and inhibition executive tasks. To our knowledge, there are no corresponding studies of bidirectional interference between temporal order memory and executive tasks. However, several experiments have combined concurrent order and duration processing in a dual-task format. Henson, Hartley, Burgess, Hitch, and Flude (2003) reported a series of studies involving the visual presentation of letter sequences. In an Item Probe (IP) condition, a single probe letter followed the letter sequence, and subjects judged whether the probe was on the list. In a List Probe (LP) condition, a letter list followed the sequence, and subjects judged whether the letter list matched the letter sequence. One study (exp. 4) required that subjects perform the IP and LP tasks both singly and concurrently with a timing task that involved synchronized tapping with a series of tones. The results showed that both probe tasks interfered with timing by increasing tapping error. In addition, the concurrent tapping task interfered with both IP and LP performance; notably, the impairment was greater for the LP (sequence judgment) task. Fortin and colleagues studied the relation between duration and order in the context of a memory search task. In one study (Fortin & Massé, 1999, exp. 1), a memory set of letters appeared sequentially on a screen. In a temporal production condition, subjects judged whether a probe letter matched any of the items in the memory set while simultaneously producing a 2-s interval via a button press. In an order-plustemporal production condition, subjects judged whether a probe letter appeared in a specified serial position within the memory set while they also produced a 2-s interval. The results showed that subjects generated longer temporal productions (indicating greater interference) in the order condition. In later research, Fortin, Champagne, and Poirier (2007, exp. 1), combined temporal production with either a spatial or temporal memory task. In the spatial task, letters appeared simultaneously in different quadrants of a square. Subjects then judged whether a probe letter had appeared in a specific location while they produced a 2.7 s interval. In the temporal task, a sequence of letters appeared one at a time in the same location. Subjects then judged whether a probe letter had appeared at a particular point within the sequence while they produced the 2.7 s interval. The results showed that increasing the size of the memory set lengthened temporal productions in the temporal memory task, but not in the spatial memory task. Fortin et al. (2007) concluded that the interference between the temporal memory and temporal production tasks occurred because the two tasks competed for the same set of central timing resources. Brown and colleagues conducted a series of dual-task interference studies designed specifically to test whether timing and sequencing or ordering tasks rely on executive attentional resources. Brown (2006) had subjects perform serial temporal production (generating a series of 5-s intervals) and random number generation (RNG) tasks both separately and concurrently. RNG is a sequencing task that requires subjects to produce a continuous series of digits in a random order. Numerous interference studies show that RNG performance depends on the same attentional resources involved in a host of other executive tasks (Baddeley, Emslie, Kolodny, & Duncan, 1998; Lemaire, Abdi, & Fayol, 1996; Robbins et al., 1996; Teasdale et al., 1995; Towse & Valentine, 1997). The dual-task conditions revealed clear evidence of bidirectional interference: RNG caused temporal productions to become longer and more variable, and timing caused the random number sequence to become less random. In another study (Brown & Merchant, 2007), subjects again performed serial temporal production and

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sequencing tasks alone and in combination. Exp. 1 involved a sequence reasoning task in which subjects evaluated statements describing the ordering of pairs of letters; exp. 2 involved a sequence monitoring task, in which subjects tracked familiar event sequences, such as an alphabetic listing of letters (A-B-C…) or an alphanumeric series of letter-number pairs (A-4, B-5, C-6…). The findings showed that the concurrent sequencing tasks interfered with timing performance and concurrent timing interfered with sequencing performance. More recently, Brown (2014) examined interference patterns between serial temporal production and two types of reasoning tasks in which subjects evaluated pairs of statements describing familiar actions. Sequence reasoning required subjects to judge whether the stated actions appeared in the correct temporal order, whereas similarity reasoning involved judging whether the statement pairs described similar objects or actions. The results showed a strong bidirectional interference effect between the timing and sequence tasks. In contrast, the similarity task interfered with timing, but was itself either unaffected by concurrent timing or affected to a significantly weaker degree. 2. The present research The present study was designed to replicate and expand on the previous research by generalizing interference effects to different experimental procedures. As before, it is a dual-task experiment; however, we instituted several critical methodological changes that differ from the previous work in this area. Because most research on temporal order relates to memory, these changes were designed to shift the focus more towards memory processing. First, we used a different sequencing task, in which subjects were required to reproduce the serial ordering of lists of words. This task places greater stress on serial memory processes, whereas previous tasks emphasized reasoning, event monitoring, or working memory. Secondly, we used a different duration judgment task, temporal reproduction. All the prior sequencing and timing studies employed some form of a temporal production task as a measure of timing performance. In contrast, reproduction involves perceiving a critical interval and then duplicating that interval, and so is more reliant on memory functioning. Some research suggests that production and reproduction may involve different cognitive mechanisms (e.g., Baudouin, Vanneste, Isingrini, & Pouthas, 2006), and so it is important to determine whether bidirectional interference effects transcend differences between the methods. Third, we had subjects judge longer intervals (14–28 s) as opposed to the shorter intervals (5 s or less) used in previous studies. These longer intervals would be expected to engage temporal memory processes to a greater degree compared with the earlier experiments. In addition to changes in the ordering and duration tasks, we also included an additional concurrent executive task (mental arithmetic) to manipulate workload demands. There is abundant evidence that mental arithmetic recruits executive attentional resources (De Rammelaere, Stuyven, & Vandierendonck, 1999; Furst & Hitch, 2000; Lemaire et al., 1996; Seitz & Schumann-Hengsteler, 2000). Furthermore, concurrent arithmetic tasks produce bidirectional interference with timing (Brown, 1997; Kantowitz & Knight, 1974, 1976; Wierwille, Rahimi, & Casali, 1985). Insofar as order processing involves executive functioning, we predict that the arithmetic task should interfere with both temporal order and duration judgment performance, and that both the order and duration judgment tasks should interfere with mental arithmetic performance. 3. Methods 3.1. Subjects Sixty-four students (14 males, 50 females) enrolled in General Psychology classes at the University of Southern Maine volunteered for

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the experiment in return for extra course credit. The average age of the students was 26.8 years. 3.2. Apparatus and stimuli An Apple computer equipped with a Timemaster II H. O. clock card (Applied Engineering) set at an interrupt rate of 1024 Hz was programmed to present stimuli and record duration judgment responses. The stimuli were 135 words taken from word norms provided by Toglia and Battig (1978); the words had familiarity ratings of 4.00– 4.99 (based on a 7-point scale). The mean length of the words was 5.6 letters (SD = 1.7). These words were formed into nine separate lists. There were three short lists (10 words each), three medium lists (15 words each), and three long lists (20 words each). 3.3. Procedure Subjects were tested individually in a single session. The nine wordlists were presented on the computer screen. The words in each list appeared one at a time for 1.4 s, with each succeeding word replacing the previous word. Thus, the wordlist presentation intervals lasted for 14 s (the 10-word lists), 21 s (the 15-word lists), and 28 s (the 20word lists). At the end of each list, subjects judged the duration of the wordlist, the temporal order of the words, or both duration and temporal order. Prior to each list, subjects were informed as to which of the temporal attributes they would be asked to judge. Three lists of each duration were associated with duration judgments, three were associated with temporal order judgments, and three were associated with both duration and temporal order judgments. The lists were presented in a uniform randomized sequence to all subjects. For the duration judgments, subjects reproduced the wordlist interval. They pressed the spacebar on the computer keyboard to mark the beginning of their judgment, and then pressed the spacebar once again when they thought that an amount of time had passed by that was equal to the wordlist interval. For the temporal order judgments, subjects were provided with a sheet listing the words in a randomized order. They were asked to rearrange the words into the original order in which they had been presented. When subjects had to judge both duration and order, they first reproduced the interval and then reordered the words2. Subjects were assigned to one of three mental workload conditions. Subjects in the control condition had no additional task requirements. They simply paid attention to the wordlists without any distractions. Subjects in the two remaining conditions performed a mental subtraction task during list presentation. As the wordlist appeared on the screen, the experimenter read a series of random 2-digit numbers to the subjects. Subjects in the n-3 condition had to subtract three from each number and state the result. Subjects in the n-7 condition subtracted seven from each number read by the experimenter. Another 2-digit number for another subtraction followed each response. This procedure continued until the wordlist ended. Thus, a continuous series of these subtraction problems was presented throughout the wordlist interval. 4. Results and discussion 4.1. Duration judgments

4.1.1. Absolute error scores Measures of absolute timing error are often sensitive at detecting interference effects in duration judgments (e.g., Brown, 1985; Brown & Boltz, 2002; Michon, 1972). Absolute error scores were created with the formula (|D − R|/D)*100. We computed the absolute difference between the actual duration (D) and the temporal reproduction (R), and then converted these values into a percentage to account for different intervals. The scores indicate how far duration judgments deviate from accuracy. The scores were submitted to a 2 × 3 × 3 mixed ANOVA. The factors were attention (duration or duration + order), workload (control, n-3 subtractions, or n-7 subtractions), and wordlist (short [14 s], medium [21 s], or long [28 s]). The analysis uncovered two significant effects (see Fig. 1). First is a main effect for workload (F(2, 61) = 4.13, p b .03, η2p = .12). Orthogonal comparisons were used to test for differences between means. Contrast 1 (control versus the two mental subtraction conditions) was significant (F(1, 61) = 7.52, p b .01, η2p = .11). This increase in error from the control (M = 18.1%, SE = 4.7) to the combined mental subtraction conditions (M = 34.1%, SE = 4.0) shows the classic interference effect of time judgments being disrupted by a concurrent distractor task. Contrast 2 (comparing the n-3 versus n-7 conditions) was not significant (F b 1). The main effect for attentional condition also was significant (F(1, 61) = 5.82, p b .02, η2p = .09). The comparison here is between attending to duration alone (M = 26.2%, SE = 2.9) versus attending to duration + order (M = 31.4%, SE = 3.1). The extra cognitive demand of attending to temporal order interfered with judgments of duration. As seen in Fig. 1, the effect applied equally across all the mental workload conditions. In fact, there was a nearly constant difference in error (averaging 5.2 percentage points) between the duration-only condition and the duration + order condition. This result shows that order processing interfered with duration processing. None of the other effects involving absolute error was significant. 4.1.2. Constant error scores We also analyzed constant error scores, which were formed by dividing each reproduction by the actual duration (i.e., R/D). Values less 50

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Mean Percent Absolute Error

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Duration judgments were converted into two different error scores for analysis. These scores measured absolute error and constant (directional) error in duration judgments. 10 2

When subjects judged temporal order only, the order judgments were delayed by the wordlist duration. This procedure was instituted to insure that these judgments would be comparable to the order judgments in the duration + temporal order condition, in which order judgments were always preceded by a reproduction response. Thus, temporal order judgments of the short list were delayed by 14 sec, judgments of the medium list were delayed by 21 sec, and judgments of the long list were delayed by 28 sec.

Control

n-3 Subtraction

n-7 Subtraction

Mental Workload Fig. 1. Mean percent absolute error scores and standard errors in duration judgments for single task (duration only) and dual task (duration + order) attentional conditions as a function of mental workload.

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than 1 signify underestimation and values greater than 1 indicate overestimation. These error scores were submitted to a 2 × 3 × 3 mixed ANOVA, which uncovered a main effect for wordlist (F(2, 122) = 3.42, p b .04, η2p = .05). The mean scores for the short, medium, and long lists were 0.99 (SE = 0.05), 0.91 (SE = 0.04), and 0.92 (SE = 0.05), respectively. Note that all these scores show underestimation (all values are less than 1). One interesting feature is that the longer lists have lower scores than the short list. This pattern resembles Vierordt's law, considered to be the oldest finding in time psychology (Lejeune & Wearden, 2009; Woodrow, 1951). Vierordt's law states that there is a tendency to give relatively longer duration judgments to the short intervals in a series, and shorter judgments to the long intervals. None of the other effects in the ANOVA was significant. 4.2. Temporal order judgments Following the procedure of Naveh-Benjamin (1990a), the temporal order judgments were converted into two standard performance measures for analysis. One measure is a modified percent correct score and the other is a correlation score. 4.2.1. Percent correct scores For each subject, we calculated the percentage of occasions that the judged position of a word was within ±1 item of the actual input position. These scores were submitted to an attention (order versus duration + order) × workload (control, n-3, or n-7) × wordlist (short, medium, or long) mixed ANOVA. All three main effects and one interaction were significant. Fig. 2 shows the effects for the workload and attentional conditions. Mental workload (F(2, 61) = 15.46, p b .001, η2p = .34) produced a steady decrease in performance on the temporal order task across the control (M = 40.6%, SE = 1.7), n-3 (M = 31.8%, SE = 1.7), and n-7 (M = 27.6%, SE = 1.7) conditions. Orthogonal contrasts were used to compare means. Contrast 1 (control versus combined subtraction conditions) was significant (F(1, 61) = 27.86, p b .001, η2p = .31). This

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result corresponds to what we found with the duration judgments. That is, the workload task interfered with both timing and order. Contrast 2 (comparing n-3 versus n-7) was not significant (p b .09). The main effect for attention (F(1, 61) = 16.15, p b .001, η2p = .21) revealed that performance was uniformly more accurate when subjects attended to order alone (M = 36.7%, SE = 1.2). In contrast, attention to order + duration impaired temporal order performance (M = 30.1%, SE = 1.3). Performance dropped by an average of 6.5 percentage points across all workload conditions. This pattern exactly parallels the timing data. The other main effect involved the wordlists (F(2, 122) = 119.51, p b .001, η2p = .66). Ordering performance was most accurate with the short lists (M = 45.9%, SE = 1.7), less so with the medium lists (M = 31.7%, SE = 1.2), and least accurate with the long lists (M = 22.4%, SE = 0.9). The linear trend (F(1, 61) = 195.08, p b .001) accounts for 98.6% of the variance. The significant attention × wordlist interaction (F(2, 122) = 3.54, p b .04, η2p = .05) was probed with simple main effects tests contrasting the three wordlists within the two attentional conditions. These tests confirmed that scores declined within both the order (F(2, 122) = 73.37, p b .001, η2p = .55) and the duration + order (F(2, 122) = 28.64, p b .001, η2p = .32) conditions. None of the other effects in the ANOVA was significant. 4.2.2. Correlation scores The other performance measure is the Pearson r correlation between the judged order of the words and their actual input order. Correlation coefficients were computed for each subject and submitted to an attention × workload × wordlist mixed ANOVA. All three factors exerted significant effects. These results essentially mirror the findings involving the percent correct scores. The effects for attention and workload are depicted in Fig. 3. Increasing workload demands from the control (M = 0.44, SE = 0.03) to the n-3 (M = 0.19, SE = 0.03) and n-7 (M = .15, SE = 0.03) conditions diminished correlation scores. Comparisons of these means showed that contrast 1 (control versus n-3 and n-7 combined) was significant (F(1, 61) = 54.81, p b .001, η2p = .47), whereas contrast 2 (n-3 versus n-7)

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Mental Workload Fig. 2. Mean percent correct scores and standard errors in temporal order judgments for single task (order only) and dual task (order + duration) attentional conditions as a function of mental workload.

Control

n-3 Subtraction

n-7 Subtraction

Mental Workload Fig. 3. Mean correlation scores and standard errors between judged word order and actual input order for single task (order only) and dual task (order + duration) attentional conditions as a function of mental workload.

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was not. These data show the same interference effect associated with mental workload that was found with the percent correct scores. The main effect for attentional condition (F(1, 61) = 20.88, p b .001, η2p = .25) revealed that when subjects attended to order alone (M = 0.32, SE = 0.02), the correlations were higher than when they attended to order + duration (M = 0.21, SE = 0.02). The workload x attention interaction (F(2, 61) = 8.00, p b .001, η2p = .21) was probed with tests of simple main effects. These tests confirmed that workload disrupted performance in both the order (F(2, 61) = 39.33, p b .001, η2p = .56) and order + duration (F(2, 61) = 6.77, p b .01, η2p = .18) conditions. A final result in the ANOVA was a main effect for the wordlists (F(2, 122) = 12.50, p b .001, η2p = .17). The mean correlation scores for the short, medium, and long lists were 0.35 (SE = 0.03), 0.24 (SE = 0.02), and 0.20 (SE = 0.02), respectively. This pattern is very similar to that of the percent correct scores. The linear trend (F(1, 61) = 19.56, p b .001) accounts for 94.0% of the variance.

in performance from the duration to the order conditions (p b .05), and from the duration to the duration + order conditions (p b .01). The worst performance (averaging 64% correct) occurred when subjects worked on difficult subtraction problems while they also had to keep track of both the duration and the ordering of the wordlist. The demands of these concurrent tasks did not leave much attention available for mental arithmetic. 5. General discussion The experiment produced a consistent set of results. The data highlight the critical role of attention in both duration and order judgments, and suggest that there is a basic correspondence between these temporal attributes. There are three primary findings, which we summarize in the following Sections. 5.1. Bidirectional interference between duration and order

4.3. Workload Performance We also evaluated performance on the mental workload task. The dependent measure is the percentage of subtraction problems that were solved correctly. These scores were computed for subjects in the two mental subtraction groups and were submitted to an attention (duration, order, and duration + order) × workload (n-3 and n-7) × wordlist (short, medium, and long) mixed ANOVA. The analysis uncovered significant effects for attention (F(2, 80) = 7.23, p b .001, η2p = .15), workload (F(1, 40) = 12.98, p b .001, η2p = .24), and the attention × workload interaction (F(2, 80) = 6.01, p b .005, η2p = .13); these effects are depicted in Fig. 4. The workload effect showed that the subjects were more accurate with the easy (n-3) subtraction problems (M = 86.9%, SE = 2.4) compared with the difficult (n-7) problems (M = 71.9%, SE = 2.4). The attention × workload interaction was submitted to an analysis of simple main effects comparing the three attentional conditions within the easy and difficult workload tasks. This analysis showed that the three attentional conditions produced differences only with the difficult problems (F(2, 80) = 12.83, p b .001, η2p = .24). As shown in Fig. 4, accuracy scores in the n-7 condition dropped steadily from the duration to order to the duration + order conditions. The implication is that these three conditions consume progressively greater amounts of attentional resources, with the result that less and less capacity is available for the subtraction task. The Tukey test for multiple comparisons was used to test for differences between means. There was a significant decrease 95

n-3 Subtraction n-7 Subtraction

Mean Percent Correct

90 85 80 75 70

The first main finding involves bidirectional interference. We found that attention to order interfered with duration judgments, and that attention to duration interfered with order judgments. The degree of interference was very similar. Dividing attention between duration and order diminished the accuracy of duration judgments by about 5 percentage points, and diminished the accuracy of ordering judgments by about 6 percentage points. This pattern of bidirectional interference has important implications for understanding the nature of the duration and ordering tasks. The mutual interference observed between duration and ordering suggests that judgments of these two temporal attributes depend upon the same attentional resources or cognitive mechanisms. Each task interferes with the other because they are in direct competition for the same resources. The findings on bidirectional interference in the present research align well with previous investigations on interference between concurrent timing and sequencing tasks. The same basic result occurred in the present study despite substantial methodological changes from the prior work, including longer intervals and different time judgment methods. Especially important is that the present study employed a more strictly memory-based ordering task as opposed to the attentional or reasoning sequence tasks used previously. Our finding of the same bidirectional interference effect between duration and ordering tasks provides strong support for the notion of a fundamental commonality between these different temporal attributes. The mutual interference between duration and order also relates to the critical issue of timing in serial order memory. Lewandowsky et al. (2006) contrasted two competing views on the role of time in theoretical accounts of serial order. Temporal distinctiveness (or time-based) theories assert that time and temporal order memory are closely linked, whereas event-based theories assign minimal or no importance of time to order memory performance. Our results support the time-based view of serial order memory. The finding that concurrent duration judgment and serial order memory tasks produce mutual interference underscores an intimate connection between these processes. Our results are consistent with the notion that serial order tasks involve establishing memory items along a temporal continuum or timeline, and then discriminating between those temporal distances at the time of retrieval (e.g., Brown et al., 2006, 2007, 2009; Farrell & McLaughlin, 2007). 5.2. Workload interference

65 60

Duration

Order

Duration + Order

Attentional Condition Fig. 4. Mean percent correct scores and standard errors for the n-3 subtraction and n-7 subtraction mental workload problems as a function of the duration, order, and duration + order attentional conditions.

The second main result concerns the effects of mental workload. The workload task interfered with duration and temporal order processing by making both types of judgments less accurate. The duration judgment data add to the large body of work cited previously concerning the interference effect in timing (e.g., Brown, 1997, 2008, 2010). Tracking the passage of time is a resource-demanding task, and anything that diverts resources away from this task will disrupt the ongoing

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processing of temporal information. In the present case, interference in temporal processing took the form of an increase in the absolute error of duration judgments, with the error nearly doubling from 18% in the single-task (duration only) condition to 34% in the dual-task (duration + workload) conditions. Mental workload had no effect on the constant error of duration judgments. Although nontemporal distractor tasks often lead to a shortening of perceived time, there are numerous instances in which interference is instead manifested as increased absolute error or variability in duration judgments (e.g., Brown, 1985, 1998; Brown & Boltz, 2002; Brown, Newcomb, & Kahrl, 1995; Goldstone, 1975; Kiefer, Riley, Shockley, Villard, & Van Orden, 2009; Michon, 1972; Schwartz, 1978). The increase in absolute error unaccompanied by any consistent change in directional error indicates that the mental workload task caused subjects to both underestimate and overestimate the actual duration. Mental workload produced a similar interference effect on temporal order judgments. Accuracy in ordering the words to match the actual input order dropped from approximately 40% correct in the single-task (temporal order only) condition to 30% correct in the dual-task (temporal order + mental workload) conditions. This outcome fits in with other research showing that concurrent distractor tasks interfere with temporal order processing (e.g., Crowder, 1978; Gisselgard, Udden, Ingvar, & Petersson, 2007; Healy, 1975, 1977; Naveh-Benjamin, 1990a). These interference effects support the idea that, as with duration judgments, temporal order judgments also require attentional resources. The easy (n-3) and difficult (n-7) versions of the mental workload task were equally disruptive for both duration judgments and temporal order judgments. Attentional resource theorists use the term difficulty insensitivity to describe this effect (Wickens, 1980, 1984). Brown's (2008) review of the timing literature noted that 67% of the studies that manipulated distractor task difficulty found that increased difficulty was associated with increased error in duration judgments. Of the studies reporting no effect of increased difficulty, most found that the different versions of the distractor task interfered equally with timing performance, as in the present case. Brown (2008) suggested that because timing performance is very sensitive to even small workload demands, in some instances further increases in demands might not degrade performance beyond an already low level. The processing demands imposed by the n-3 and n-7 tasks may not have been sufficiently different to produce differential interference effects. 5.3. Temporal processing and workload performance A bidirectional interference effect also occurred between the temporal tasks and the workload task. Not only did the mental workload task interfere with duration judgment and temporal order memory performance, but also, at least under certain conditions, the duration and temporal order tasks interfered with workload performance. Specifically, the duration and ordering tasks interfered with workload performance when subjects worked on the difficult version of the workload task. This pattern ties in with the theoretical and empirical work described previously that relates timing, temporal order, and mental arithmetic to executive cognitive functions. The implication is that all three tasks tap into the same pool of executive resources, and so any combination of these tasks leads to competition for the same resources, with the result that performance on all tasks suffers. The interference effects involving mental workload performance also reveal another interesting feature. As subjects worked on the n-7 mental arithmetic problems, there was a progressive deterioration in performance from the concurrent duration (M = 81.3% correct) to ordering (M = 70.3% correct) to duration + ordering (M = 64.0% correct) conditions. This pattern suggests that the temporal order task may demand more of the resources supporting mental arithmetic than does the duration judgment task. Furthermore, the combination of duration processing and order processing (the duration + ordering condition) produced the greatest decrement in workload performance,

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implying that the resource demands of the two temporal attribute tasks were additive. Future studies on this topic may address some of the limitations of the present experiment and expand the scope of the research. Most temporal order research involves verbal stimuli (letters or words), as in the present case. It would strengthen the results if it were shown that the same pattern occurred with non-verbal stimuli, such as musical or pictorial sequences. Our study indicated that an executive workload task (mental arithmetic) influenced both duration and temporal order judgments. Future research may include a non-executive workload task, which would allow for a direct comparison of the effects of executive and non-executive demands on duration and order processing. Yet another approach would be to test special subject populations known to have impairments in temporal order processing, such as individuals with dyslexia (Jaskowski & Rusiak, 2008; Liddle, Jackson, Rorden, & Jackson, 2009). 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