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Associative learning of response inhibition affects perceived duration in a subsequent temporal bisection task
Acta Psychologica 201 (2019) 102952
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Associative learning of response inhibition affects perceived duration in a subsequent temporal bisection task
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Paul Sowman, Jordan Wehrman Macquarie University, 16 University Ave, Macquarie University, 2109, Macquarie Park, NSW, Australia
A B S T R A C T
Interval timing, the ability to discern the duration of an event, is integral to appropriately navigating the world, from crossing the road to catching a ball. Several features of an event can affect its perceived duration, for example it has previously been shown that a large stimulus is perceived to last longer than a small stimulus. In the current article, participants performed either a Go/No-Go or variable foreperiod task prior to performing a temporal bisection task. In both the Go/No-Go and variable foreperiod tasks, participants learned an association between a particular response and a particular stimulus. Subsequently, the perceived duration of these stimuli was tested in a temporal bisection task. Our findings indicated that associating a stimulus with response inhibition (i.e. a No-Go stimulus) decreased perceived duration compared to a stimulus associated with a response (a Go stimulus). Associating a stimulus with either a short or long foreperiod, on the other hand, did not affect perceived duration. We relate this finding back to the coding efficiency theory and the processing principle. A No-Go stimulus requires more cognitive processing than a Go stimulus and would thus be predicted to increase, rather than decrease, perceived duration in both these time perception theories. Finally, we suggest how our findings might be used in future investigations of interval timing.
1. Introduction While objectively, one second is no more or less than a tick of the second hand, subjectively, a second can expand and contract. For example, an infrequent stimulus is perceived to last longer than a frequent one (Matthews & Gheorghiu, 2016; Tse, Intriligator, Rivest, & Cavanagh, 2004; Wehrman, Wearden, & Sowman, 2018). Further, the length of a stimulus can change the perception of a following interval, either expanding its perceived duration (Wehrman, Wearden, & Sowman, 2018) or contracting it (Bausenhart, Dyjas, & Ulrich, 2014), depending on the context. One proposal for how subjective duration diverges from objective duration is the ‘processing principle’ (see Matthews & Meck, 2016). In their article, Matthews and Meck (2016) specify three drivers of perceived duration; bottom-up perceptual effects, top-down attentional effects and memory-driven effects. In the memory category, an interesting finding is that those stimuli to which participants have been previously exposed tend to be perceived as lasting longer than otherwise. For example, memorising a set of words will result in those words, as well as semantically-related words, having an expanded subjective duration in a subsequent duration perception task (Masson & Caldwell, 1998; Ono & Kawahara, 2008; Paller, Mayes, McDermott, Pickering, & Meudell, 1991; Witherspoon & Allan, 1985). While exposure to previous stimuli have been shown to affect perceived duration, in the current experiments we examined the possibility of associative learning similarly driving interval timing.
Specifically, we required participants to perform either a Go/No-Go (NG) task (Experiment 1) or a variable foreperiod (FP) task (Experiment 2). These tasks severed to form an association between stimuli and either explicit, response, inhibition (Experiment 1) or with implicit, temporally induced, inhibition (Experiment 2). We then had participants perform a temporal bisection task. Crucially, the same stimulus set was used for both the conditioning and temporal bisection tasks. By doing this, we were able to interrogate the effects of associations made between stimulus and response in the conditioning task upon the perception of duration in the bisection task. We ask whether the context in which a stimulus is learned affects duration perception in a subsequent task. In other words, can how we learn a stimulus affect how we perceive its duration in future? It is known that concurrently performing reactive inhibitory control tasks and timing tasks result in bidirectional interference (Brown, Johnson, Sohl, & Dumas, 2015; Brown & Perreault, 2017), a finding that links reactive inhibitory control and timing. This interference has been proposed to be due to overlapping cognitive requirements, specifically executive control resources (Brown, 2006). The current experiments expand on these findings by asking whether an association of a stimulus with reactive inhibitory control also affects duration perception. Additionally, we investigate whether associative learning of proactive inhibitory control might also affect perceived duration. More generally, if prior exposure to a stimulus results in expanded perceived duration, as with words in the Paller et al. (1991) article, then we expect that exposure to a stimulus which reactively or proactively
E-mail addresses: [email protected] (P. Sowman), [email protected] (J. Wehrman). https://doi.org/10.1016/j.actpsy.2019.102952 Received 7 June 2019; Received in revised form 22 September 2019; Accepted 31 October 2019 0001-6918/ © 2019 Elsevier B.V. All rights reserved.
Acta Psychologica 201 (2019) 102952
P. Sowman and J. Wehrman
FP is thus defined as the duration from the start of the trial until the presentation of a response imperative, with a longer FP indicating a longer ‘waiting’ time between the ready signal and the response. Generally, the longer the FP, the faster participants respond (see Los, 2010, 2013). For example, in a two FP experiment, participants tend to respond faster after the long FP compared to the short FP. Because a response imperative is possible at the short FP, participants ready a response at this time. However, when this FP is passed without a response imperative appearing, proactive inhibitory control is applied to suppress the release of a response. Several lines of evidence support this view. MacKinnon et al. (2013) showed that a startling stimulus will result in an unintended response closer to a FP which has previously been associated with a response rather than at a duration not previously associated with response. For example, in the two FP experiment, a startle at the short FP will more often result in a response even in the absence of a response imperative, compared to when the startle is presented midway between the short and long FPs. This demonstrates that an increase in motor excitability occurs at a known (for example, short) FP. Further, transcranial magnetic stimulation studies show that increased excitability is accompanied by increased inhibitory control which functions to withhold the prepotent response from being released unintentionally (e.g. Hasbroucq, Kaneko, Akamatsu, & Possamaı ̈, 1997; Sinclair & Hammond, 2009). Thus, while the variable FP task requires proactive, or implicit, inhibitory control to repress premature response release, the Go/NG task requires reactive, or explicit, inhibitory control to prevent a readied response (Aron, 2011; Los, 2013). In the current task, we preferentially link one of two responses to the short FP and another to the long FP. By doing this, participants learn to make a specific response at a given FP (Thomaschke, Kiesel, & Hoffmann, 2011; Thomaschke, Kunchulia, & Dreisbach, 2015), an effect demonstrated by faster RTs when the FP is linked to its preferred response. By associating one response to the short FP, we are linking one signal to the implicit inhibitory control that is applied when the short FP is passed. Though the links between a variable FP task and duration perception are less well established than the link with the Go/NG task, there is some evidence that conditioning using a variable FP task may have an effect on duration perception. Firstly, Grondin and Rammsayer (2003) and Wehrman et al. (2018b) demonstrate that a longer FP prior to the presentation of a timed stimulus increases the perceived duration of that stimulus (see also, Mo & George, 1977). Because the expectation of a stimulus increases as the FP continues, participants tend to more strongly expect a stimulus to occur at the longer FP. This increased expectation of a stimulus occurring at the long FP has been proposed to result in an earlier perceived onset of the stimulus, in turn resulting in a longer perceived duration of the stimulus presented at the long, rather than short, FP (see Lin & Shimojo, 2017). This same reasoning can be applied to RT results, participants perceive the onset of a stimulus earlier at the long FP and so respond faster (e.g. Los, 2013; Los & van den Heuvel, 2001). If this is the case, then perhaps creating an association between one stimulus and the long FP can have a carryover effect such that participants will report the long FP-associated stimulus as lasting longer due to it being perceived earlier in the conditioning task. Alternatively, a longer FP may result in improved temporal resolution (see Bausenhart, Rolke, & Ulrich, 2008) which could affect perceived duration in another task by subsequently improved processing of specifically that stimulus (vis-à-vis the processing principle, see Matthews & Meck, 2016).2 An alternative mechanism that might affect perceived duration is the implicit inhibition applied at the short FP in the case where the
requires inhibition should result in an expanded sense of duration. This is because, while participants may simply respond to an uninhibited stimulus, a stimulus which requires inhibition is additionally salient, requiring the withholding of a prepotent response, as will be discussed below. In the next section, we introduce the conditioning tasks, and why we specifically chose these as our tools for forming stimulus associations. Following this, we introduce the temporal bisection task used to investigate duration perception. 1.1. Go/NG The classic Go/NG task (Donders, 1969) presents participants with one of two possible signals, either a Go signal to which participants react as quickly as possible, or a NG signal to which participants withhold their response. It is thought that prior to the presentation of a stimulus, participant responses are held on the verge of release in order to respond quickly (e.g. MacKinnon, Allen, Shiratori, & Rogers, 2013; Valls-Solé, Rothwell, Goulart, Cossu, & Munoz, 1999, 1995). When a stimulus is presented, participants release this prepotent response. If a NG is presented, participants must reactively inhibit their response to prevent it from being completed (see Aron, 2011; Eapen et al., 2017). Here, participants performed a Go/NG task in which they responded to one signal and withheld their response to another (a square or hexagon, counterbalanced between participants). These signals were presented with equal probability. Though the equal presentation of Go and NG signals likely reduced the prepotency of the response, it avoids the confound of biased exposure to one signal over another, which could lead to similar effects found in the word learning experiments mentioned above. Further, equiprobable Go/NG tasks have been performed in several places in the literature, and have been shown to elicit similar electrophysiological processes to frequent Go versus infrequent NG types of tasks (Bokura, Yamaguchi, & Kobayashi, 2001; Bruin & Wijers, 2002; Nieuwenhuis, Yeung, van den Wildenberg, & Ridderinkhof, 2003), in similar locations in the brain (Vallesi, McIntosh, & Stuss, 2009; Mostofsky et al., 2003; Garavan, Hester, Murphy, Fassbender, & Kelly, 2006; Rubia et al., 2001; Watanabe et al., 2002). Two known effects in the literature indicate that associative learning using a Go/NG task may affect perception in a subsequent task. Firstly, prior research has shown that concurrent performance of a Go/ NG task interferes with time-based tasks (Brown et al., 2015; Brown & Perreault, 2017), as do other inhibitory control tasks (Castro-Meneses & Sowman, 2018). Thus, we know that the inhibitory control required in a Go/NG task can affect timing performance, though not necessarily duration perception. Secondly, Go/NG associations have been used to manipulate future decisions. For example, associating a NG signal with unhealthy foods can result in people choosing less unhealthy food in future (e.g. Houben & Jansen, 2015).1 This demonstrates that a NG signal can affect non-concurrent performance on an unrelated task. Together, these findings indicate that it may be possible for a nonconcurrent Go/NG task to affect timing as measured in a subsequent bisection task. Specifically, because a NG signal should be more salient than a Go signal, we expect that a NG signal will be perceived to last a longer duration than a Go signal in the temporal bisection task. 1.2. Variable FP In the variable FP task, participants are required to respond to some signal at some point in time. Each trial is generally initiated with a ready signal. After the ready signal, one of two (or more) fixed durations are presented (i.e. FPs), terminated by a response imperative. The
2 Indeed, a temporally expected stimulus has been proposed to increase the amount of information gathered from that stimulus over a given period of time (see Rohenkohl, Cravo, Wyart, & Nobre, 2012; Vangilde, Coull, & Bundesen, 2012; Vangkilde, Petersen, & Bundesen, 2013).
1 Houben and Jansen (2015) also used equiprobable signals, still finding effects on subsequent behaviour.
2
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were coloured grey (RGB: 127;127;127). The mapping between the shapes and Go/NG was counterbalanced between participants. Each trial consisted of a blank screen lasting a random duration between 300 ms and 1000 ms, followed by the response imperative signal which was presented for 300 ms. Participants were required to press the spacebar within 100–800 ms of the stimulus onset for the response to be considered correct. If participants responded to a Go signal within the time limit, their response was counted as correct, otherwise it was incorrect. 500 ms after the offset of the signal, response feedback was presented for 500 ms, displaying the word ‘Good’ or ‘Miss,’ depending on whether the response was correct or not. The next trial then started. After the Go/NG block, participants watched a duration acclimatization block. In this section, a filled grey circle (150 pixel diameter) was presented for 700 ms followed by a 400 ms–600 ms random duration blank screen. The next 700 ms grey circle was then presented. This was repeated 20 times. Finally, participants performed 4 blocks of 70 trials in which they were required to judge whether the stimulus, either the Go or NG from the Go/NG block, was presented for Shorter or Longer than the standard from the acclimatization phase. Each trial consisted of one of the two stimuli presented for a random duration between 300 ms and 1100 ms (controlled by the screen refresh rate), followed by a 500 ms blank screen and then a question mark presented until response. Participants responded by pressing the ‘L’ and ‘S’ key on a standard keyboard, indicating a Longer or Shorter judgment, respectively. Following a participant’s response, there was a blank screen of between 400 ms and 600 ms prior to the next trial. The general trial format is shown in Fig. 1 below.
imperative occurs at the long FP i.e. when a response is withheld at the short FP. Previous theories speculate that both the Go/NG task and variable FP tasks affect expectation (Los & van den Heuvel, 2001). Los (2013) showed that implicit inhibitory control applied at the short FP affected RTs similarly to the explicit inhibitory control applied in response to a NG signal. Therefore, though perhaps not equivalent forms of inhibitory control, the passing of the short FP (proactive control) may affect perceived duration in the same direction as a NG signal (reactive control). This would then result in participants reporting that short FP associated stimuli last longer than long FP associated stimuli. 1.3. Bisection task Temporal bisection has been a preferred method for investigating duration perception for a number of years (e.g. Church & Deluty, 1977; Wearden, 1991). In the current article, we used a ‘reference-free’ bisection task, similar to that used in Wiener, Thompson, and Coslett (2014)). Participants were first shown several 700 ms standard durations. Following this initial learning phase, participants were shown stimuli of durations ranging from 300 ms to 1100 ms and required to judge whether the stimulus duration was Shorter or Longer than the standard duration. By fitting a psychometric function to the resulting responses, we can estimate the point at which participants perceive a stimulus to be the same duration as the standard (called the point of subjective equality, PSE). While the PSE is the primary measure of interest, we also analyse two other supplementary statistics. Response uncertainty can be quantified by measuring RTs; participants tend to respond slower when more uncertain of their responses (see Balcı & Simen, 2014). Generally, a condition with longer RTs correspond to a later PSE (see Birngruber, Schröter, Schütt, & Ulrich, 2018; Birngruber, Schröter, & Ulrich, 2014; Dyjas & Ulrich, 2014). Further, we measured participants sensitivity to changes in duration by estimating the Weber Ratio (WR), a function of the slope of the psychometric curve.
2.4. Analysis The first 5 trials of the bisection task were discarded from analysis, as were the first 3 trials of the association-building task. Analysis was performed using R (R-Core-Team, 2015), and the ‘quickpsy’ (Linares & Lopez-Moliner, 2016) packages. We estimated psychometric functions based on the proportion of times the participant indicated that the target was longer than the standard. The quickpsy program fits a cumulative normal function to the data using direct likelihood maximization by nonparametric bootstrapping of 1000 samples (see Linares & Lopez-Moliner, 2016, for further information). From the psychometric function, the PSE, defined as the point where the probability of a ‘longer’ response was 50%, was estimated. The WR was calculated as
2. Experiment 1: Go/NG association 2.1. Participants 20 participants were included in Experiment 1. Their mean age was 20.9 years (SD = 4.8), with 8 males, and 3 left-handed participants. This experiment (as well as Experiment 2) were approved by the human ethics committee of Macquarie University, and conducted in accord with the Helsinki Declaration. Participants were recruited from participation pools in exchange for course credit or $5AUD. The experiment took approximately 20 min. 2.2. Equipment Experimental stimuli were presented on a Samsung SyncMaster SA950 (27 inch) monitor controlled by a Dell Optiplex 9010 PC (8 GB RAM, 3.2 Ghz Intel i5-3470 CPU) running 64-bit Windows 7. All experiments took place in dimly lit rooms with participants seated 0.8 m away from their monitor. Neurobehavioral System’s Presentation (v18.3) was used to present the experiments. 2.3. Task description Participants were instructed at the beginning of the experiment not to perform rhythmic activity, such as tapping or counting (see Grondin & Killeen, 2009). Participants first completed a Go/NG task consisting of 70 trials. In each trial participants were shown either a Go or NG signal such that at the completion of the task they had seen each signal 35 times in total. The two signals were either a hexagon with a radius of 110 pixels, or a square with a radius of 75 pixels. These were sized such that the area each stimulus covered on the screen was approximately equal. Both
Fig. 1. General outline of a single trial of the Go/NG experiment. The top sequence shows the initial Go/NG task, while the bottom sequence shows the duration question task. The question mark appeared until a participant responded. This was followed by a 400–600 ms blank screen prior to the initiation of the next trial. 3
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Fig. 2. Left: Effect of prior Go and NG association with perceived duration. Error bars represent one standard error of the mean. Right: Average proportion of ‘Long’ responses across each binned duration. Note that actual analysis was based on psychometric function fitted on individual data. Inset is a magnification close to the PSE, with one standard error of the mean presented. The dotted lines represent the PSE.
nor NG stimulus were significantly different than the objective standard duration of 700 ms however (Go: t(19) = .838, p = .413, d = .19; NG: t(19) = 1.48, p = .156, d = .33). There was no significant effect of the stimulus association on the WR (t(19) = .675, p = .508, d = .15). The mean WR was 0.16; duration discriminability did not significantly change given either a Go or NG associated stimulus.
the objective duration difference between when participants chose Long 75% and 25% of the time, dividing by 2 and normalising by the PSE. This measure was used to quantify the change discriminability under each condition. To analyse RTs in the bisection task, we discarded trials with RTs longer than 4000 ms as outliers and then segmented the RTs into 10 equally sized test durations of 80 ms each. The middle of each of these was taken as the dependant variable; 340 ms, 420 ms, 500 ms, 580 ms, 660 ms, 740 ms, 820 ms, 900 ms, 980 ms and 1060 ms.
3. Experiment 2: variable FP association 3.1. Participants
2.5. Results In Experiment 2, 2 participants were replaced due to not responding appropriately in the timing task (i.e. responding to the stimuli presented rather than the duration). The mean age was 19.9 years (SD = 3.1), with 8 males, and 2 left-handed participants.
The mean RT in the Go/NG task was 364 ms (s.d. = 35 ms) and the average percent correct was 99.0% (s.d. = 1.8%). No further analysis was performed on this data. Firstly, we performed an ANOVA on the mean probability of participants responding Long across 10 equally sized groups; 340 ms, 420 ms, 500 ms, 580 ms, 660 ms, 740 ms, 820 ms, 900 ms, 980 ms and 1060 ms. The probability of the participant responding Long was the dependent variable and the binned duration and whether the stimulus was associated with a Go or NG were the independent variables. In this ANOVA there was a main effect of the binned-duration (F(9, 171) = 236.7, p < .001, Greenhouse-Geisser (GG) sphericity corrected, ηp2 = .93). The probability of participants responding Long tended to increase as the objective duration of the stimulus increased (as example: mean p(Long) at 340 ms = .025, mean p(Long) at 1060 ms = .930). This was as expected, and not analysed further. There was also a main effect of whether the stimulus was associated with a Go (p(Long) = .49) or a NG (p(Long) = .48; F(1, 19) = 4.77, p = .042, ηp2 = .20). The interaction effect was not significant (F(9, 171) = .728, p = .607, GG sphericity corrected, ηp2 = .04). See Fig. 2, Right, for mean participant responses. For the RT analysis, 0.1% of trials were discarded after being classified as slow responses. Mean RTs were analysed in a similar ANOVA design to the probability of participants responding Long. There was a main effect of binned duration (F(9, 171) = 5.49, p = .001, GG sphericity corrected, ηp2 = .22). As expected, the closer to the standard 700 ms duration the test stimulus was, the longer were participant RTs.3 This was not analysed further. There was no effect of whether the target stimulus was associated with a Go or NG (mean RT = 390 ms and 395 ms, respectively, F(1, 19) = .000, p = .998, ηp2 = .00). The interaction effect was also not significant (F(9, 171) = 1.03, p = .414, ηp2 = .05). Next, we analysed the derived measures from the psychometric functions. A Welch’s paired t-test showed that if the target image was previously linked to a NG signal, then participants had a higher PSE (mean = 730 ms) than if the image was linked with a Go response (mean = 715 ms, t(19) = 2.26, p = .036, d = .50; Fig. 2, Left, Right inset). If an image was linked with a NG, it was perceived to last for a shorter duration than a signal associated with a Go. The PSEs of a Go
3.2. Task description The equipment used and analysis performed were as per Experiment 1. Both the acclimatization and bisection tasks were the same as in Experiment 1, the conditioning task was the only difference between experiments. In the conditioning task, participants performed a variable FP task consisting of 1 block of 70 trials. Each trial started with a fixation cross (“+” printed in white at 150 point font) presented for 300 ms. Following this, a blank screen was presented for either 300 ms or 900 ms, the short and long FPs, respectively. After the blank screen, either the square or hexagon (the same stimuli as Experiment 1) was presented for 300 ms. Participants responded with either the ‘Z’ or ‘M’ keys to one of the shapes, counterbalanced between participants. Each of the two shapes were preferentially associated with one of the two FPs. In 30 out of the 70 trials, one shape was associated with one of the FPs, and in 5 out of the 70 trials that shape was associated with the other FP. Note, if only one shape was presented at each FP, participants could just respond based on the FP. This would make the actual stimulus irrelevant, and thus the visual stimulus in the second part of the experiment would not necessarily be associated with the FP. Therefore, we chose to have a majority of each stimulus associated with a single FP, rather than an exclusive relationship. Following the presentation of the response imperative, the RT limits were as per Experiment 1; the correct response had to be made between 100 ms and 800 ms of the onset of the response imperative. 800 ms after the onset of the response imperative, the words ‘Good’ or ‘Miss’ were displayed for 500 ms. The general format of each trial is as per Fig. 1 above, except that each trial started with a fixation cross, and the blank screen preceding the response imperative lasted either 300 ms or 900 ms. 3.3. Results The mean RT for the initial conditioning task was 400 ms (s.d. = 50 ms) with a mean of 91.5% correct (i.e. within the RT limit and the correct response was given, s.d. = 6.3%). We performed an ANOVA on the RTs, with mean RT as the dependent variable, and the
3
As examples: mean RT at the 340 ms (extreme short) = 322 ms, Mean RT at the 660 ms (middle) = 477 ms, Mean RT at the 740 ms (middle) = 470 ms, mean RT at the 1060 ms (extreme long) = 340 ms. 4
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4. Discussion
independent variables of FP duration and whether the response was to the frequent or infrequent stimulus at a given FP. RTs were significantly shorter following a long (394 ms) compared to short FP (413 ms; F(1, 19) = 6.99, p = .016, ηp2 = .27). Further, RTs were significantly shorter following the stimulus which was frequently presented at a given FP (396 ms) compared to the stimulus presented infrequently (411 ms; F(1, 19) = 5.92, p = .025, ηp2 = .24).4 The interaction between FP duration and response frequency was not significant (F(1, 19) = .225, p = .640, ηp2 = .01). Overall, participants responded slower when a short FP was presented, and further, were slower when an infrequent response was required at a given FP. Together, these are the results expected in this type of task (see Thomaschke et al., 2011, 2015), and indicate that participants had learned the FP durations, and successfully associated a given FP to a given response. As per Experiment 1, we initially ran an ANOVA on the probability of participants responding Long at each of the given duration bins under each condition. The dependent variable in this case was the probability of a response being Long, and the independent variable was the binned duration of the test stimulus, and whether the test stimulus was preferentially shown at the short or long FP. There was a main effect of the binned duration (F(9, 171) = 216.7, p < .001, ηp2 = .92). The longer the duration of the test stimulus, the more likely a participant would respond Long (as examples: p(Long) to 340 ms bin = .040, p(Long) to 1060 ms bin = .908). This was as expected and not analysed further. There was no main effect of the stimulus shape presented (F(1, 19) = .020, p = .890, ηp2 = .00, both long FP and short FP p(Long) = .48). The interaction between the binned duration and the stimulus presented was also not significant (F(9, 171) = .808, p = .610, ηp2 = .04). 0.5% of trials were discarded as slow responses in the RT analysis. There was a significant effect of the binned duration on RTs (F(4, 76) = 6.17, p = .002, GG sphericity corrected, ηp2 = .25). As per Experiment 1, RTs were slower when the test duration was closer to the objective standard duration (700 ms).5 Again, this was not analysed further. There was also a main effect of whether the image was associated with the long or short FP (F(1, 19) = 4.40, p = .0496, ηp2 = .19). RTs were longer if the stimulus was previously associated with a long FP (421 ms) rather than a short FP (405 ms, Fig. 3, Right). The interaction effect between the binned duration and the association of the image approached significance (F(4, 76) = 2.40, p = .058, ηp2 = .11). We next analysed the derived measures from the psychometric function. There was no significant effect of whether the image presented was associated with the short or long FP on the PSE (t(19) = .119, p = .906, d = .03). The mean PSE for the image associated with the long FP was 726 ms and for the image associated with the short FP was 727 ms. Neither of these were significantly longer than the 700 ms objective duration of the standard (t(19) = 1.07, p = .299, d = .24; t(19) = 1.27, p = .221, d = .28, for long and short FP images, respectively). There was no significant effect of which FP a stimulus was associated with on the WR (t(19) = 1.63, p = .119, d = .36). The mean WR was .18. Together the derived measures from the psychometric functions indicate no shift in how long a stimulus is perceived to last, nor how easy it is to discriminate its duration, based on its FP association.
In Experiment 1, we demonstrated that stimuli associated with a NG signal in a prior Go/NG task were reported to last for a shorter duration compared to when they were associated with a Go signal. This manifested as a longer point of subjective equality (PSE) following a NG-, rather than Go-associated, stimulus. Broadly, this finding indicates that the associations made in a previous experiment can be carried over to another task in which they affect duration perception. However, the direction of this effect was not expected; the processing principle would seem to indicate that a NG stimulus should be perceived to last longer than a Go stimulus. We will discuss possible reasons for this below. In Experiment 2, there was no effect of FP association on the PSE. This did not appear to be due to the initial conditioning task ineffectively creating an association between response and FP duration; RTs in the conditioning task were faster given a stimulus presented at its frequently associated FP. Despite no PSE effect, RTs in the bisection task were significantly faster following a stimulus associated with a short, rather than long, FP. This RT effect cannot be attributed to participants learning when to react during the conditioning phase; RTs in the initial task were faster following a long FP rather than a short FP. One possible cause of the RT pattern found in Experiment 2 is participants became accustomed to waiting longer for the long FP associated symbol to appear in the variable FP task. When the long FP stimulus appeared in the bisection task, participants were less prepared and so took longer to respond. Alternatively, it has previously been shown that PSE and RTs are both informative of timing processes (e.g. Balcı & Simen, 2014; Birngruber et al., 2014, 2018; Dyjas & Ulrich, 2014). Thus, perhaps a long FP association resulted in participants being more unsure of response given a longer test duration, indicating a shorter perceived duration. While this would be in line with an inhibition-based interpretation of the short FP association (essentially the reverse of the discussion in the following section), without a PSE effect, further research is required in this regard. Possible methods for these future investigations are discussed below. 4.1. Processing principle and coding efficiency Under the processing principle (Matthews & Meck, 2016), we would expect that stimuli which are easier to process will be perceived to last a longer duration. Similarly, another theory of time perception, the coding efficiency theory (Eagleman, 2008; Eagleman & Pariyadath, 2009) speculates that perceived duration is a correlate of the size of the neural response to a given stimulus. Both these theories explain several phenomena in time perception research. For example a novel stimulus is often found to last subjectively longer than a common, repeated, stimulus (Matthews & Gheorghiu, 2016; Wehrman et al., 2018b). Under the processing principle, a novel stimulus is easier to process, while coding efficiency posits that the longer duration of the novel stimulus is due to it eliciting a larger neural response. In Experiment 1, a NG associated stimulus resulted in a shorter perceived duration compared with a Go associated stimulus. However, a common finding in the inhibitory control literature is that a NG stimulus results in an inhibitory stopping mechanism which essentially adds a neural response on top of the Go response. Thus, a NG results in a larger neural response compared to a Go signal (Falkenstein, Hoormann, & Hohnsbein, 1999; Smith, Jamadar, Provost, & Michie, 2013). Given this, the NG signal would be expected to be more salient, and under both the processing principle and coding efficiency theories, would lead to a longer perceived duration. Prior findings have shown an interference between concurrent timing and inhibition (Brown et al., 2015; Brown & Perreault, 2017), and thus the two are unlikely to be fully separable processes either over time or processing location (see also, Arnal, 2012; Fujioka, Trainor, Large, & Ross, 2012; Schubotz, Friederici, & Yves von Cramon, 2000). One possible reason for this difference is that following a NG
4 It could be argued that because there are few (10) trials in the uncommon condition, then a non-parametric t-test should be run. Thus, we additionally ran a Wilcoxon signed rank test, which confirmed the findings of the parametric test (p = .015). 5 As examples: mean RT at the 340 ms (extreme short) = 361 ms, Mean RT at the 660 ms (middle) = 484 ms, Mean RT at the 740 ms (middle) = 474 ms, mean RT at the 1060 ms (extreme long) = 369 ms.
5
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Fig. 3. Left: Average proportion of ‘Long’ responses across each binned duration. Note that actual analysis was based on psychometric function fitted on individual data. Right: Effect of prior Short and Long FP association on mean RTs. Error bars represent one standard error of the mean.
test this, a higher number of stimuli could be used. For example four stimuli could be used, and only one symbol associated with a NG. Participants are then still exposed to equal numbers of each stimuli, but the probability of stopping decreases, making stopping more difficult (see Aron, 2011). Further, providing stricter RT limits also makes stopping more difficult and thus may be another approach to increase the inhibitory load associated with one stimulus. Alternatively, Go/NG or variable FP blocks could be intermixed (or the number of trials increased) with bisection blocks, providing a 'top-up' to the association between the stimulus types and the responses made. Specifically in terms of reactive inhibitory control, perhaps the stop-signal task could be used in future, requiring a more difficult stop to occur after a response has been initiated. The current article provides a blueprint for these proposed future investigations. Other aspects of time perception could also be investigated using a method similar to the current study. Similar to the effects of a Go/NG task on a non-concurrent duration judgment task, future research could use other associative learning tasks to investigate the mechanisms of time perception. For example, conditioning participants to associate a stimulus with being larger or smaller may affect duration perception. Whether expected magnitude, rather than actual magnitude (a known modifier of perceived duration, e.g. Rammsayer & Verner, 2015), affects perceived duration remains an open question.
associated stimulus, participants were simply more likely to choose a Short response. Though this result would not require adjusting the coding efficiency or processing principle theories, as it is a post-timing judgment process, why this bias would be consistent across participants to the point that a statistical effect is present is not obvious. Or, rather than being judgment based, perhaps the onset of timing is simply later when presented with the NG-associated stimulus, corresponding to when a stopping process occurred (i.e. after the Go process). Again, this would not require any changes to either of the theories mentioned, as the timing occurred in the same manner as normal, but it just started later, resulting in a shorter perceived duration (see Lin & Shimojo, 2017, for the application of similar logic to another temporal illusion). Finally, perhaps the association with inhibition slowed down the accrual of information over time.6 In a RT task, this would be advantageous, applying inhibition ‘pumps the breaks’ on a response being released, allowing more time to stop a response (see race models, e.g. Logan, Cowan, & Davis, 1984). When presenting an inhibition associated stimulus in the bisection task, there is also this slowed information accrual, resulting in less units of information collected over a given interval, and thus a shorter perceived duration. This explanation is in line with a processing principle understanding of interval timing, but perhaps not the coding efficiency theory. Further investigation is required to disentangle these possibilities. 4.2. Practical implications
5. Conclusion
The use of a task to create associations between a symbol and a response has, until now, not been used to mediate duration perception. However, other methods of creating ‘inhibition’ have been shown to affect perceived duration. For example, Mioni et al. (2016) used transcranial direct current stimulus to investigate the role of primary visual (V1) and auditory (A1) cortices in temporal bisection. They found that using cathodal stimulation over V1 caused an increase in WR, indicating more variable duration estimates when V1 was inhibited. Further, Kanai, Lloyd, Bueti, and Walsh (2011) applied theta-burst transcranial magnetic stimulation over V1 and A1, finding that the magnetically induced inhibition of V1 resulted in the underestimation of visually presented stimulus durations. The current experiment additionally indicates that behavioural methods of response inhibition induction can affect perceived duration in some instances.
In this article, we showed that associating a stimulus with a Go rather than NG signal affected subsequent duration judgments. These associations were not present when associating stimuli with different FPs in a variable FP task, in terms of PSE. However, in the variable FP case, RTs were slower following a long FP associated stimulus. The main contribution of this paper is twofold. Firstly, the possible effects of proactive and reactive inhibitory control on perceived duration have not previously been investigated. The experiments performed here demonstrate that overt inhibition of a response in a Go/NG context produces changes in duration perception. However, using a similar task requiring implicit inhibition of a response, as occurs in the variable FP task, did not produce an equivalent duration illusion. Secondly, this article provides proof-of-concept that an unrelated task may be used to form associations which subsequently affect perceived duration.
4.3. Future directions Declaration of Competing Interest
In the current research, the effect of associating a NG rather than a Go with a target stimulus resulted in a reduced perceived duration of 15 ms (a medium-sized effect). If reactive inhibitory control can indeed affect perceived duration, a more difficult inhibitory control task may increase the difference in PSE between Go- and NG-related stimuli. To
None.
Acknowledgements PS was supported by funding from the Australian Research Council (DE130100868andDP170103148).
6 Specifically, this could be as per a drift-diffusion model; a NG stimulus could result in a slower drift towards response.
6
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Associative learning of response inhibition affects perceived duration in a subsequent temporal bisection task
T
Paul Sowman, Jordan Wehrman Macquarie University, 16 University Ave, Macquarie University, 2109, Macquarie Park, NSW, Australia
A B S T R A C T
Interval timing, the ability to discern the duration of an event, is integral to appropriately navigating the world, from crossing the road to catching a ball. Several features of an event can affect its perceived duration, for example it has previously been shown that a large stimulus is perceived to last longer than a small stimulus. In the current article, participants performed either a Go/No-Go or variable foreperiod task prior to performing a temporal bisection task. In both the Go/No-Go and variable foreperiod tasks, participants learned an association between a particular response and a particular stimulus. Subsequently, the perceived duration of these stimuli was tested in a temporal bisection task. Our findings indicated that associating a stimulus with response inhibition (i.e. a No-Go stimulus) decreased perceived duration compared to a stimulus associated with a response (a Go stimulus). Associating a stimulus with either a short or long foreperiod, on the other hand, did not affect perceived duration. We relate this finding back to the coding efficiency theory and the processing principle. A No-Go stimulus requires more cognitive processing than a Go stimulus and would thus be predicted to increase, rather than decrease, perceived duration in both these time perception theories. Finally, we suggest how our findings might be used in future investigations of interval timing.
1. Introduction While objectively, one second is no more or less than a tick of the second hand, subjectively, a second can expand and contract. For example, an infrequent stimulus is perceived to last longer than a frequent one (Matthews & Gheorghiu, 2016; Tse, Intriligator, Rivest, & Cavanagh, 2004; Wehrman, Wearden, & Sowman, 2018). Further, the length of a stimulus can change the perception of a following interval, either expanding its perceived duration (Wehrman, Wearden, & Sowman, 2018) or contracting it (Bausenhart, Dyjas, & Ulrich, 2014), depending on the context. One proposal for how subjective duration diverges from objective duration is the ‘processing principle’ (see Matthews & Meck, 2016). In their article, Matthews and Meck (2016) specify three drivers of perceived duration; bottom-up perceptual effects, top-down attentional effects and memory-driven effects. In the memory category, an interesting finding is that those stimuli to which participants have been previously exposed tend to be perceived as lasting longer than otherwise. For example, memorising a set of words will result in those words, as well as semantically-related words, having an expanded subjective duration in a subsequent duration perception task (Masson & Caldwell, 1998; Ono & Kawahara, 2008; Paller, Mayes, McDermott, Pickering, & Meudell, 1991; Witherspoon & Allan, 1985). While exposure to previous stimuli have been shown to affect perceived duration, in the current experiments we examined the possibility of associative learning similarly driving interval timing.
Specifically, we required participants to perform either a Go/No-Go (NG) task (Experiment 1) or a variable foreperiod (FP) task (Experiment 2). These tasks severed to form an association between stimuli and either explicit, response, inhibition (Experiment 1) or with implicit, temporally induced, inhibition (Experiment 2). We then had participants perform a temporal bisection task. Crucially, the same stimulus set was used for both the conditioning and temporal bisection tasks. By doing this, we were able to interrogate the effects of associations made between stimulus and response in the conditioning task upon the perception of duration in the bisection task. We ask whether the context in which a stimulus is learned affects duration perception in a subsequent task. In other words, can how we learn a stimulus affect how we perceive its duration in future? It is known that concurrently performing reactive inhibitory control tasks and timing tasks result in bidirectional interference (Brown, Johnson, Sohl, & Dumas, 2015; Brown & Perreault, 2017), a finding that links reactive inhibitory control and timing. This interference has been proposed to be due to overlapping cognitive requirements, specifically executive control resources (Brown, 2006). The current experiments expand on these findings by asking whether an association of a stimulus with reactive inhibitory control also affects duration perception. Additionally, we investigate whether associative learning of proactive inhibitory control might also affect perceived duration. More generally, if prior exposure to a stimulus results in expanded perceived duration, as with words in the Paller et al. (1991) article, then we expect that exposure to a stimulus which reactively or proactively
E-mail addresses: [email protected] (P. Sowman), [email protected] (J. Wehrman). https://doi.org/10.1016/j.actpsy.2019.102952 Received 7 June 2019; Received in revised form 22 September 2019; Accepted 31 October 2019 0001-6918/ © 2019 Elsevier B.V. All rights reserved.
Acta Psychologica 201 (2019) 102952
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FP is thus defined as the duration from the start of the trial until the presentation of a response imperative, with a longer FP indicating a longer ‘waiting’ time between the ready signal and the response. Generally, the longer the FP, the faster participants respond (see Los, 2010, 2013). For example, in a two FP experiment, participants tend to respond faster after the long FP compared to the short FP. Because a response imperative is possible at the short FP, participants ready a response at this time. However, when this FP is passed without a response imperative appearing, proactive inhibitory control is applied to suppress the release of a response. Several lines of evidence support this view. MacKinnon et al. (2013) showed that a startling stimulus will result in an unintended response closer to a FP which has previously been associated with a response rather than at a duration not previously associated with response. For example, in the two FP experiment, a startle at the short FP will more often result in a response even in the absence of a response imperative, compared to when the startle is presented midway between the short and long FPs. This demonstrates that an increase in motor excitability occurs at a known (for example, short) FP. Further, transcranial magnetic stimulation studies show that increased excitability is accompanied by increased inhibitory control which functions to withhold the prepotent response from being released unintentionally (e.g. Hasbroucq, Kaneko, Akamatsu, & Possamaı ̈, 1997; Sinclair & Hammond, 2009). Thus, while the variable FP task requires proactive, or implicit, inhibitory control to repress premature response release, the Go/NG task requires reactive, or explicit, inhibitory control to prevent a readied response (Aron, 2011; Los, 2013). In the current task, we preferentially link one of two responses to the short FP and another to the long FP. By doing this, participants learn to make a specific response at a given FP (Thomaschke, Kiesel, & Hoffmann, 2011; Thomaschke, Kunchulia, & Dreisbach, 2015), an effect demonstrated by faster RTs when the FP is linked to its preferred response. By associating one response to the short FP, we are linking one signal to the implicit inhibitory control that is applied when the short FP is passed. Though the links between a variable FP task and duration perception are less well established than the link with the Go/NG task, there is some evidence that conditioning using a variable FP task may have an effect on duration perception. Firstly, Grondin and Rammsayer (2003) and Wehrman et al. (2018b) demonstrate that a longer FP prior to the presentation of a timed stimulus increases the perceived duration of that stimulus (see also, Mo & George, 1977). Because the expectation of a stimulus increases as the FP continues, participants tend to more strongly expect a stimulus to occur at the longer FP. This increased expectation of a stimulus occurring at the long FP has been proposed to result in an earlier perceived onset of the stimulus, in turn resulting in a longer perceived duration of the stimulus presented at the long, rather than short, FP (see Lin & Shimojo, 2017). This same reasoning can be applied to RT results, participants perceive the onset of a stimulus earlier at the long FP and so respond faster (e.g. Los, 2013; Los & van den Heuvel, 2001). If this is the case, then perhaps creating an association between one stimulus and the long FP can have a carryover effect such that participants will report the long FP-associated stimulus as lasting longer due to it being perceived earlier in the conditioning task. Alternatively, a longer FP may result in improved temporal resolution (see Bausenhart, Rolke, & Ulrich, 2008) which could affect perceived duration in another task by subsequently improved processing of specifically that stimulus (vis-à-vis the processing principle, see Matthews & Meck, 2016).2 An alternative mechanism that might affect perceived duration is the implicit inhibition applied at the short FP in the case where the
requires inhibition should result in an expanded sense of duration. This is because, while participants may simply respond to an uninhibited stimulus, a stimulus which requires inhibition is additionally salient, requiring the withholding of a prepotent response, as will be discussed below. In the next section, we introduce the conditioning tasks, and why we specifically chose these as our tools for forming stimulus associations. Following this, we introduce the temporal bisection task used to investigate duration perception. 1.1. Go/NG The classic Go/NG task (Donders, 1969) presents participants with one of two possible signals, either a Go signal to which participants react as quickly as possible, or a NG signal to which participants withhold their response. It is thought that prior to the presentation of a stimulus, participant responses are held on the verge of release in order to respond quickly (e.g. MacKinnon, Allen, Shiratori, & Rogers, 2013; Valls-Solé, Rothwell, Goulart, Cossu, & Munoz, 1999, 1995). When a stimulus is presented, participants release this prepotent response. If a NG is presented, participants must reactively inhibit their response to prevent it from being completed (see Aron, 2011; Eapen et al., 2017). Here, participants performed a Go/NG task in which they responded to one signal and withheld their response to another (a square or hexagon, counterbalanced between participants). These signals were presented with equal probability. Though the equal presentation of Go and NG signals likely reduced the prepotency of the response, it avoids the confound of biased exposure to one signal over another, which could lead to similar effects found in the word learning experiments mentioned above. Further, equiprobable Go/NG tasks have been performed in several places in the literature, and have been shown to elicit similar electrophysiological processes to frequent Go versus infrequent NG types of tasks (Bokura, Yamaguchi, & Kobayashi, 2001; Bruin & Wijers, 2002; Nieuwenhuis, Yeung, van den Wildenberg, & Ridderinkhof, 2003), in similar locations in the brain (Vallesi, McIntosh, & Stuss, 2009; Mostofsky et al., 2003; Garavan, Hester, Murphy, Fassbender, & Kelly, 2006; Rubia et al., 2001; Watanabe et al., 2002). Two known effects in the literature indicate that associative learning using a Go/NG task may affect perception in a subsequent task. Firstly, prior research has shown that concurrent performance of a Go/ NG task interferes with time-based tasks (Brown et al., 2015; Brown & Perreault, 2017), as do other inhibitory control tasks (Castro-Meneses & Sowman, 2018). Thus, we know that the inhibitory control required in a Go/NG task can affect timing performance, though not necessarily duration perception. Secondly, Go/NG associations have been used to manipulate future decisions. For example, associating a NG signal with unhealthy foods can result in people choosing less unhealthy food in future (e.g. Houben & Jansen, 2015).1 This demonstrates that a NG signal can affect non-concurrent performance on an unrelated task. Together, these findings indicate that it may be possible for a nonconcurrent Go/NG task to affect timing as measured in a subsequent bisection task. Specifically, because a NG signal should be more salient than a Go signal, we expect that a NG signal will be perceived to last a longer duration than a Go signal in the temporal bisection task. 1.2. Variable FP In the variable FP task, participants are required to respond to some signal at some point in time. Each trial is generally initiated with a ready signal. After the ready signal, one of two (or more) fixed durations are presented (i.e. FPs), terminated by a response imperative. The
2 Indeed, a temporally expected stimulus has been proposed to increase the amount of information gathered from that stimulus over a given period of time (see Rohenkohl, Cravo, Wyart, & Nobre, 2012; Vangilde, Coull, & Bundesen, 2012; Vangkilde, Petersen, & Bundesen, 2013).
1 Houben and Jansen (2015) also used equiprobable signals, still finding effects on subsequent behaviour.
2
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were coloured grey (RGB: 127;127;127). The mapping between the shapes and Go/NG was counterbalanced between participants. Each trial consisted of a blank screen lasting a random duration between 300 ms and 1000 ms, followed by the response imperative signal which was presented for 300 ms. Participants were required to press the spacebar within 100–800 ms of the stimulus onset for the response to be considered correct. If participants responded to a Go signal within the time limit, their response was counted as correct, otherwise it was incorrect. 500 ms after the offset of the signal, response feedback was presented for 500 ms, displaying the word ‘Good’ or ‘Miss,’ depending on whether the response was correct or not. The next trial then started. After the Go/NG block, participants watched a duration acclimatization block. In this section, a filled grey circle (150 pixel diameter) was presented for 700 ms followed by a 400 ms–600 ms random duration blank screen. The next 700 ms grey circle was then presented. This was repeated 20 times. Finally, participants performed 4 blocks of 70 trials in which they were required to judge whether the stimulus, either the Go or NG from the Go/NG block, was presented for Shorter or Longer than the standard from the acclimatization phase. Each trial consisted of one of the two stimuli presented for a random duration between 300 ms and 1100 ms (controlled by the screen refresh rate), followed by a 500 ms blank screen and then a question mark presented until response. Participants responded by pressing the ‘L’ and ‘S’ key on a standard keyboard, indicating a Longer or Shorter judgment, respectively. Following a participant’s response, there was a blank screen of between 400 ms and 600 ms prior to the next trial. The general trial format is shown in Fig. 1 below.
imperative occurs at the long FP i.e. when a response is withheld at the short FP. Previous theories speculate that both the Go/NG task and variable FP tasks affect expectation (Los & van den Heuvel, 2001). Los (2013) showed that implicit inhibitory control applied at the short FP affected RTs similarly to the explicit inhibitory control applied in response to a NG signal. Therefore, though perhaps not equivalent forms of inhibitory control, the passing of the short FP (proactive control) may affect perceived duration in the same direction as a NG signal (reactive control). This would then result in participants reporting that short FP associated stimuli last longer than long FP associated stimuli. 1.3. Bisection task Temporal bisection has been a preferred method for investigating duration perception for a number of years (e.g. Church & Deluty, 1977; Wearden, 1991). In the current article, we used a ‘reference-free’ bisection task, similar to that used in Wiener, Thompson, and Coslett (2014)). Participants were first shown several 700 ms standard durations. Following this initial learning phase, participants were shown stimuli of durations ranging from 300 ms to 1100 ms and required to judge whether the stimulus duration was Shorter or Longer than the standard duration. By fitting a psychometric function to the resulting responses, we can estimate the point at which participants perceive a stimulus to be the same duration as the standard (called the point of subjective equality, PSE). While the PSE is the primary measure of interest, we also analyse two other supplementary statistics. Response uncertainty can be quantified by measuring RTs; participants tend to respond slower when more uncertain of their responses (see Balcı & Simen, 2014). Generally, a condition with longer RTs correspond to a later PSE (see Birngruber, Schröter, Schütt, & Ulrich, 2018; Birngruber, Schröter, & Ulrich, 2014; Dyjas & Ulrich, 2014). Further, we measured participants sensitivity to changes in duration by estimating the Weber Ratio (WR), a function of the slope of the psychometric curve.
2.4. Analysis The first 5 trials of the bisection task were discarded from analysis, as were the first 3 trials of the association-building task. Analysis was performed using R (R-Core-Team, 2015), and the ‘quickpsy’ (Linares & Lopez-Moliner, 2016) packages. We estimated psychometric functions based on the proportion of times the participant indicated that the target was longer than the standard. The quickpsy program fits a cumulative normal function to the data using direct likelihood maximization by nonparametric bootstrapping of 1000 samples (see Linares & Lopez-Moliner, 2016, for further information). From the psychometric function, the PSE, defined as the point where the probability of a ‘longer’ response was 50%, was estimated. The WR was calculated as
2. Experiment 1: Go/NG association 2.1. Participants 20 participants were included in Experiment 1. Their mean age was 20.9 years (SD = 4.8), with 8 males, and 3 left-handed participants. This experiment (as well as Experiment 2) were approved by the human ethics committee of Macquarie University, and conducted in accord with the Helsinki Declaration. Participants were recruited from participation pools in exchange for course credit or $5AUD. The experiment took approximately 20 min. 2.2. Equipment Experimental stimuli were presented on a Samsung SyncMaster SA950 (27 inch) monitor controlled by a Dell Optiplex 9010 PC (8 GB RAM, 3.2 Ghz Intel i5-3470 CPU) running 64-bit Windows 7. All experiments took place in dimly lit rooms with participants seated 0.8 m away from their monitor. Neurobehavioral System’s Presentation (v18.3) was used to present the experiments. 2.3. Task description Participants were instructed at the beginning of the experiment not to perform rhythmic activity, such as tapping or counting (see Grondin & Killeen, 2009). Participants first completed a Go/NG task consisting of 70 trials. In each trial participants were shown either a Go or NG signal such that at the completion of the task they had seen each signal 35 times in total. The two signals were either a hexagon with a radius of 110 pixels, or a square with a radius of 75 pixels. These were sized such that the area each stimulus covered on the screen was approximately equal. Both
Fig. 1. General outline of a single trial of the Go/NG experiment. The top sequence shows the initial Go/NG task, while the bottom sequence shows the duration question task. The question mark appeared until a participant responded. This was followed by a 400–600 ms blank screen prior to the initiation of the next trial. 3
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Fig. 2. Left: Effect of prior Go and NG association with perceived duration. Error bars represent one standard error of the mean. Right: Average proportion of ‘Long’ responses across each binned duration. Note that actual analysis was based on psychometric function fitted on individual data. Inset is a magnification close to the PSE, with one standard error of the mean presented. The dotted lines represent the PSE.
nor NG stimulus were significantly different than the objective standard duration of 700 ms however (Go: t(19) = .838, p = .413, d = .19; NG: t(19) = 1.48, p = .156, d = .33). There was no significant effect of the stimulus association on the WR (t(19) = .675, p = .508, d = .15). The mean WR was 0.16; duration discriminability did not significantly change given either a Go or NG associated stimulus.
the objective duration difference between when participants chose Long 75% and 25% of the time, dividing by 2 and normalising by the PSE. This measure was used to quantify the change discriminability under each condition. To analyse RTs in the bisection task, we discarded trials with RTs longer than 4000 ms as outliers and then segmented the RTs into 10 equally sized test durations of 80 ms each. The middle of each of these was taken as the dependant variable; 340 ms, 420 ms, 500 ms, 580 ms, 660 ms, 740 ms, 820 ms, 900 ms, 980 ms and 1060 ms.
3. Experiment 2: variable FP association 3.1. Participants
2.5. Results In Experiment 2, 2 participants were replaced due to not responding appropriately in the timing task (i.e. responding to the stimuli presented rather than the duration). The mean age was 19.9 years (SD = 3.1), with 8 males, and 2 left-handed participants.
The mean RT in the Go/NG task was 364 ms (s.d. = 35 ms) and the average percent correct was 99.0% (s.d. = 1.8%). No further analysis was performed on this data. Firstly, we performed an ANOVA on the mean probability of participants responding Long across 10 equally sized groups; 340 ms, 420 ms, 500 ms, 580 ms, 660 ms, 740 ms, 820 ms, 900 ms, 980 ms and 1060 ms. The probability of the participant responding Long was the dependent variable and the binned duration and whether the stimulus was associated with a Go or NG were the independent variables. In this ANOVA there was a main effect of the binned-duration (F(9, 171) = 236.7, p < .001, Greenhouse-Geisser (GG) sphericity corrected, ηp2 = .93). The probability of participants responding Long tended to increase as the objective duration of the stimulus increased (as example: mean p(Long) at 340 ms = .025, mean p(Long) at 1060 ms = .930). This was as expected, and not analysed further. There was also a main effect of whether the stimulus was associated with a Go (p(Long) = .49) or a NG (p(Long) = .48; F(1, 19) = 4.77, p = .042, ηp2 = .20). The interaction effect was not significant (F(9, 171) = .728, p = .607, GG sphericity corrected, ηp2 = .04). See Fig. 2, Right, for mean participant responses. For the RT analysis, 0.1% of trials were discarded after being classified as slow responses. Mean RTs were analysed in a similar ANOVA design to the probability of participants responding Long. There was a main effect of binned duration (F(9, 171) = 5.49, p = .001, GG sphericity corrected, ηp2 = .22). As expected, the closer to the standard 700 ms duration the test stimulus was, the longer were participant RTs.3 This was not analysed further. There was no effect of whether the target stimulus was associated with a Go or NG (mean RT = 390 ms and 395 ms, respectively, F(1, 19) = .000, p = .998, ηp2 = .00). The interaction effect was also not significant (F(9, 171) = 1.03, p = .414, ηp2 = .05). Next, we analysed the derived measures from the psychometric functions. A Welch’s paired t-test showed that if the target image was previously linked to a NG signal, then participants had a higher PSE (mean = 730 ms) than if the image was linked with a Go response (mean = 715 ms, t(19) = 2.26, p = .036, d = .50; Fig. 2, Left, Right inset). If an image was linked with a NG, it was perceived to last for a shorter duration than a signal associated with a Go. The PSEs of a Go
3.2. Task description The equipment used and analysis performed were as per Experiment 1. Both the acclimatization and bisection tasks were the same as in Experiment 1, the conditioning task was the only difference between experiments. In the conditioning task, participants performed a variable FP task consisting of 1 block of 70 trials. Each trial started with a fixation cross (“+” printed in white at 150 point font) presented for 300 ms. Following this, a blank screen was presented for either 300 ms or 900 ms, the short and long FPs, respectively. After the blank screen, either the square or hexagon (the same stimuli as Experiment 1) was presented for 300 ms. Participants responded with either the ‘Z’ or ‘M’ keys to one of the shapes, counterbalanced between participants. Each of the two shapes were preferentially associated with one of the two FPs. In 30 out of the 70 trials, one shape was associated with one of the FPs, and in 5 out of the 70 trials that shape was associated with the other FP. Note, if only one shape was presented at each FP, participants could just respond based on the FP. This would make the actual stimulus irrelevant, and thus the visual stimulus in the second part of the experiment would not necessarily be associated with the FP. Therefore, we chose to have a majority of each stimulus associated with a single FP, rather than an exclusive relationship. Following the presentation of the response imperative, the RT limits were as per Experiment 1; the correct response had to be made between 100 ms and 800 ms of the onset of the response imperative. 800 ms after the onset of the response imperative, the words ‘Good’ or ‘Miss’ were displayed for 500 ms. The general format of each trial is as per Fig. 1 above, except that each trial started with a fixation cross, and the blank screen preceding the response imperative lasted either 300 ms or 900 ms. 3.3. Results The mean RT for the initial conditioning task was 400 ms (s.d. = 50 ms) with a mean of 91.5% correct (i.e. within the RT limit and the correct response was given, s.d. = 6.3%). We performed an ANOVA on the RTs, with mean RT as the dependent variable, and the
3
As examples: mean RT at the 340 ms (extreme short) = 322 ms, Mean RT at the 660 ms (middle) = 477 ms, Mean RT at the 740 ms (middle) = 470 ms, mean RT at the 1060 ms (extreme long) = 340 ms. 4
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4. Discussion
independent variables of FP duration and whether the response was to the frequent or infrequent stimulus at a given FP. RTs were significantly shorter following a long (394 ms) compared to short FP (413 ms; F(1, 19) = 6.99, p = .016, ηp2 = .27). Further, RTs were significantly shorter following the stimulus which was frequently presented at a given FP (396 ms) compared to the stimulus presented infrequently (411 ms; F(1, 19) = 5.92, p = .025, ηp2 = .24).4 The interaction between FP duration and response frequency was not significant (F(1, 19) = .225, p = .640, ηp2 = .01). Overall, participants responded slower when a short FP was presented, and further, were slower when an infrequent response was required at a given FP. Together, these are the results expected in this type of task (see Thomaschke et al., 2011, 2015), and indicate that participants had learned the FP durations, and successfully associated a given FP to a given response. As per Experiment 1, we initially ran an ANOVA on the probability of participants responding Long at each of the given duration bins under each condition. The dependent variable in this case was the probability of a response being Long, and the independent variable was the binned duration of the test stimulus, and whether the test stimulus was preferentially shown at the short or long FP. There was a main effect of the binned duration (F(9, 171) = 216.7, p < .001, ηp2 = .92). The longer the duration of the test stimulus, the more likely a participant would respond Long (as examples: p(Long) to 340 ms bin = .040, p(Long) to 1060 ms bin = .908). This was as expected and not analysed further. There was no main effect of the stimulus shape presented (F(1, 19) = .020, p = .890, ηp2 = .00, both long FP and short FP p(Long) = .48). The interaction between the binned duration and the stimulus presented was also not significant (F(9, 171) = .808, p = .610, ηp2 = .04). 0.5% of trials were discarded as slow responses in the RT analysis. There was a significant effect of the binned duration on RTs (F(4, 76) = 6.17, p = .002, GG sphericity corrected, ηp2 = .25). As per Experiment 1, RTs were slower when the test duration was closer to the objective standard duration (700 ms).5 Again, this was not analysed further. There was also a main effect of whether the image was associated with the long or short FP (F(1, 19) = 4.40, p = .0496, ηp2 = .19). RTs were longer if the stimulus was previously associated with a long FP (421 ms) rather than a short FP (405 ms, Fig. 3, Right). The interaction effect between the binned duration and the association of the image approached significance (F(4, 76) = 2.40, p = .058, ηp2 = .11). We next analysed the derived measures from the psychometric function. There was no significant effect of whether the image presented was associated with the short or long FP on the PSE (t(19) = .119, p = .906, d = .03). The mean PSE for the image associated with the long FP was 726 ms and for the image associated with the short FP was 727 ms. Neither of these were significantly longer than the 700 ms objective duration of the standard (t(19) = 1.07, p = .299, d = .24; t(19) = 1.27, p = .221, d = .28, for long and short FP images, respectively). There was no significant effect of which FP a stimulus was associated with on the WR (t(19) = 1.63, p = .119, d = .36). The mean WR was .18. Together the derived measures from the psychometric functions indicate no shift in how long a stimulus is perceived to last, nor how easy it is to discriminate its duration, based on its FP association.
In Experiment 1, we demonstrated that stimuli associated with a NG signal in a prior Go/NG task were reported to last for a shorter duration compared to when they were associated with a Go signal. This manifested as a longer point of subjective equality (PSE) following a NG-, rather than Go-associated, stimulus. Broadly, this finding indicates that the associations made in a previous experiment can be carried over to another task in which they affect duration perception. However, the direction of this effect was not expected; the processing principle would seem to indicate that a NG stimulus should be perceived to last longer than a Go stimulus. We will discuss possible reasons for this below. In Experiment 2, there was no effect of FP association on the PSE. This did not appear to be due to the initial conditioning task ineffectively creating an association between response and FP duration; RTs in the conditioning task were faster given a stimulus presented at its frequently associated FP. Despite no PSE effect, RTs in the bisection task were significantly faster following a stimulus associated with a short, rather than long, FP. This RT effect cannot be attributed to participants learning when to react during the conditioning phase; RTs in the initial task were faster following a long FP rather than a short FP. One possible cause of the RT pattern found in Experiment 2 is participants became accustomed to waiting longer for the long FP associated symbol to appear in the variable FP task. When the long FP stimulus appeared in the bisection task, participants were less prepared and so took longer to respond. Alternatively, it has previously been shown that PSE and RTs are both informative of timing processes (e.g. Balcı & Simen, 2014; Birngruber et al., 2014, 2018; Dyjas & Ulrich, 2014). Thus, perhaps a long FP association resulted in participants being more unsure of response given a longer test duration, indicating a shorter perceived duration. While this would be in line with an inhibition-based interpretation of the short FP association (essentially the reverse of the discussion in the following section), without a PSE effect, further research is required in this regard. Possible methods for these future investigations are discussed below. 4.1. Processing principle and coding efficiency Under the processing principle (Matthews & Meck, 2016), we would expect that stimuli which are easier to process will be perceived to last a longer duration. Similarly, another theory of time perception, the coding efficiency theory (Eagleman, 2008; Eagleman & Pariyadath, 2009) speculates that perceived duration is a correlate of the size of the neural response to a given stimulus. Both these theories explain several phenomena in time perception research. For example a novel stimulus is often found to last subjectively longer than a common, repeated, stimulus (Matthews & Gheorghiu, 2016; Wehrman et al., 2018b). Under the processing principle, a novel stimulus is easier to process, while coding efficiency posits that the longer duration of the novel stimulus is due to it eliciting a larger neural response. In Experiment 1, a NG associated stimulus resulted in a shorter perceived duration compared with a Go associated stimulus. However, a common finding in the inhibitory control literature is that a NG stimulus results in an inhibitory stopping mechanism which essentially adds a neural response on top of the Go response. Thus, a NG results in a larger neural response compared to a Go signal (Falkenstein, Hoormann, & Hohnsbein, 1999; Smith, Jamadar, Provost, & Michie, 2013). Given this, the NG signal would be expected to be more salient, and under both the processing principle and coding efficiency theories, would lead to a longer perceived duration. Prior findings have shown an interference between concurrent timing and inhibition (Brown et al., 2015; Brown & Perreault, 2017), and thus the two are unlikely to be fully separable processes either over time or processing location (see also, Arnal, 2012; Fujioka, Trainor, Large, & Ross, 2012; Schubotz, Friederici, & Yves von Cramon, 2000). One possible reason for this difference is that following a NG
4 It could be argued that because there are few (10) trials in the uncommon condition, then a non-parametric t-test should be run. Thus, we additionally ran a Wilcoxon signed rank test, which confirmed the findings of the parametric test (p = .015). 5 As examples: mean RT at the 340 ms (extreme short) = 361 ms, Mean RT at the 660 ms (middle) = 484 ms, Mean RT at the 740 ms (middle) = 474 ms, mean RT at the 1060 ms (extreme long) = 369 ms.
5
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Fig. 3. Left: Average proportion of ‘Long’ responses across each binned duration. Note that actual analysis was based on psychometric function fitted on individual data. Right: Effect of prior Short and Long FP association on mean RTs. Error bars represent one standard error of the mean.
test this, a higher number of stimuli could be used. For example four stimuli could be used, and only one symbol associated with a NG. Participants are then still exposed to equal numbers of each stimuli, but the probability of stopping decreases, making stopping more difficult (see Aron, 2011). Further, providing stricter RT limits also makes stopping more difficult and thus may be another approach to increase the inhibitory load associated with one stimulus. Alternatively, Go/NG or variable FP blocks could be intermixed (or the number of trials increased) with bisection blocks, providing a 'top-up' to the association between the stimulus types and the responses made. Specifically in terms of reactive inhibitory control, perhaps the stop-signal task could be used in future, requiring a more difficult stop to occur after a response has been initiated. The current article provides a blueprint for these proposed future investigations. Other aspects of time perception could also be investigated using a method similar to the current study. Similar to the effects of a Go/NG task on a non-concurrent duration judgment task, future research could use other associative learning tasks to investigate the mechanisms of time perception. For example, conditioning participants to associate a stimulus with being larger or smaller may affect duration perception. Whether expected magnitude, rather than actual magnitude (a known modifier of perceived duration, e.g. Rammsayer & Verner, 2015), affects perceived duration remains an open question.
associated stimulus, participants were simply more likely to choose a Short response. Though this result would not require adjusting the coding efficiency or processing principle theories, as it is a post-timing judgment process, why this bias would be consistent across participants to the point that a statistical effect is present is not obvious. Or, rather than being judgment based, perhaps the onset of timing is simply later when presented with the NG-associated stimulus, corresponding to when a stopping process occurred (i.e. after the Go process). Again, this would not require any changes to either of the theories mentioned, as the timing occurred in the same manner as normal, but it just started later, resulting in a shorter perceived duration (see Lin & Shimojo, 2017, for the application of similar logic to another temporal illusion). Finally, perhaps the association with inhibition slowed down the accrual of information over time.6 In a RT task, this would be advantageous, applying inhibition ‘pumps the breaks’ on a response being released, allowing more time to stop a response (see race models, e.g. Logan, Cowan, & Davis, 1984). When presenting an inhibition associated stimulus in the bisection task, there is also this slowed information accrual, resulting in less units of information collected over a given interval, and thus a shorter perceived duration. This explanation is in line with a processing principle understanding of interval timing, but perhaps not the coding efficiency theory. Further investigation is required to disentangle these possibilities. 4.2. Practical implications
5. Conclusion
The use of a task to create associations between a symbol and a response has, until now, not been used to mediate duration perception. However, other methods of creating ‘inhibition’ have been shown to affect perceived duration. For example, Mioni et al. (2016) used transcranial direct current stimulus to investigate the role of primary visual (V1) and auditory (A1) cortices in temporal bisection. They found that using cathodal stimulation over V1 caused an increase in WR, indicating more variable duration estimates when V1 was inhibited. Further, Kanai, Lloyd, Bueti, and Walsh (2011) applied theta-burst transcranial magnetic stimulation over V1 and A1, finding that the magnetically induced inhibition of V1 resulted in the underestimation of visually presented stimulus durations. The current experiment additionally indicates that behavioural methods of response inhibition induction can affect perceived duration in some instances.
In this article, we showed that associating a stimulus with a Go rather than NG signal affected subsequent duration judgments. These associations were not present when associating stimuli with different FPs in a variable FP task, in terms of PSE. However, in the variable FP case, RTs were slower following a long FP associated stimulus. The main contribution of this paper is twofold. Firstly, the possible effects of proactive and reactive inhibitory control on perceived duration have not previously been investigated. The experiments performed here demonstrate that overt inhibition of a response in a Go/NG context produces changes in duration perception. However, using a similar task requiring implicit inhibition of a response, as occurs in the variable FP task, did not produce an equivalent duration illusion. Secondly, this article provides proof-of-concept that an unrelated task may be used to form associations which subsequently affect perceived duration.
4.3. Future directions Declaration of Competing Interest
In the current research, the effect of associating a NG rather than a Go with a target stimulus resulted in a reduced perceived duration of 15 ms (a medium-sized effect). If reactive inhibitory control can indeed affect perceived duration, a more difficult inhibitory control task may increase the difference in PSE between Go- and NG-related stimuli. To
None.
Acknowledgements PS was supported by funding from the Australian Research Council (DE130100868andDP170103148).
6 Specifically, this could be as per a drift-diffusion model; a NG stimulus could result in a slower drift towards response.
6
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