proceedings of the aristotelian society
issue 3 | volume cxiii | 2012 - 2013
Perceiving the Passing of Time
ian phillips university college london
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proceedings of the aristotelian society 134th session
issue no. 3 volume cx111 2012 - 2013
perceiving the passing of time
ian phillips university college london
m o n d a y, 2 2 a p r i l 2 0 1 3 17.30 - 19.15
the woburn suite senate house university of london malet street london wc1e 7hu united kingdom
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biography Ian Phillips is a Lecturer in the Philosophy Department at University College London. Before that he was a Fellow by Examination at All Souls College, Oxford University. Ian is the author of numerous articles in the philosophy of mind and cognitive science, one of which was recently awarded the William James Prize for Contributions to the Scientific Study of Consciousness. He is currently writing a book on our experience of time.
editorial note The following paper is a draft version that can only be cited with the author’s permission. The final paper will be published in Proceedings of the Aristotelian Society, Issue No. 2, Volume CXIII (2013). Please visit the Society’s website for subscription information:
perceiving the passing of time ian phillips ! Duration distortions familiar from trauma present an apparent counter-example to what we might call the naïve view of duration perception. I argue that this appearance is generated by a questionable conception of duration perception according to which we perceive duration relative to a subject-independent metric (e.g., in seconds). By way of antidote, I develop an alternative picture of duration perception on which it is our non-perceptual mental activity which provides our measure of perceived duration. I end by suggesting that certain data traditionally appealed to in support of internal clock models of timing may be more illuminatingly understood in terms of the idea that mental activity provides our measure of perceived duration.
SURVIVORS of life-threatening danger reliably report that the traumatic events which they experienced appeared to last much longer than events of the same objective length in normal conditions: ‘time seemed to slow down’ for them. As well as being of intrinsic interest, such cases are often said to reveal something about the nature of duration perception in general. In particular, such experiences have, in different ways, been thought to show the untenability of what we might call the naïve view of duration perception (§§1-2). I argue that traumatic distortions of duration present a counterexample to the naïve view only if we accept a certain conception of duration perception. According to this conception, we are not merely aware of the relative durations of events (e.g., that one event lasted twice as long as another) but are additionally aware of the ‘absolute’ durations of individual events, that is of their durations relative to a subjectindependent metric (e.g., in seconds). This conception of duration perception is not mandatory, however. By way of antidote, I develop an alternative picture of duration perception. This picture agrees that we are aware of more than just the relative durations of perceived events. However, it denies we are aware of durations relative to any subjectindependent metric. Instead, it proposes that we are aware of the durations of perceived events relative to our concurrent non-perceptual mental activity (§3).
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By appeal to the idea that we perceive durations relative to concurrent mental activity, I show how we can explain what is happening in trauma consistent with the naïve view (§4) and further defend it against a secondary objection arising from the so-called ‘oddball’ illusion (§5). I conclude by suggesting that certain data traditionally accounted for in terms of an internal clock model of timing may be more illuminatingly understood by appeal to the idea that we perceive duration in part relative to our concurrent mental activity (§6).
i. THE NAÏVE VIEW The naïve view of duration perception comprises two claims. The first is simply the idea that we are perceptually aware of the durations of events in our environment. As Foster puts it: ‘duration and change through time seem to be presented to us with the same phenomenal immediacy as homogeneity and variation of colour’ (1982: 255). Call this realism about perceived duration.1 To introduce the second aspect of the naïve view of duration perception, we need to recognize that temporal experience is a special case of perceptual experience. There is no temptation to think that when we experience a red round tomato, or a loud high-pitched sound, that our experience of these objects is itself red and round, or loud and highpitched. Our experiences, at least in their subjective aspect, do not have colours or shapes, pitches or intensities. On the other hand, our experiences do manifestly have temporal properties, being processes or events which persist through time and occur before and after one another. This raises a special question which fails to arise in other cases of perception, namely, how do the temporal properties of experience relate to the temporal properties of what is experienced? Or, in more traditional terminology, how does act time relate to object time? A traditional, if much maligned, answer to this question is eloquently voiced by Helmholtz who asserts that the only case in which ‘our perceptions can truly correspond with outer reality, is that of the timesuccession of phenomena’ (1867/1925: 445; quoted in James 1890: 628). ‘Events,’ says Helmholtz, ‘like our perceptions of them, take place in !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! 1
Cf. Dainton (2000: 115) who takes realism to be a ‘phenomenological constraint’ on theorizing in this area, ‘an obvious truth’, the ‘most basic of facts’. For contrastingly sceptical views about realism see Le Poidevin 2007 and Chuard 2011
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time, so that the time-relations of the latter can furnish a true copy of those of the former.’ In the case of duration the idea would be that, if we experience an event as having a certain duration, then our experience itself will persist through time for a matching period. This idea receives support from reflection on our experience. Imagine hearing a singer sustaining a long note for several seconds. Then ask yourself, how long did your experience of the note itself last? The natural answer is that your experience lasted just as long as the note apparently lasted.2 There are thus two aspects to our initial intuitive conception of duration perception: realism and what we might call matching, the claim that whenever our experience apparently presents us with an event with a certain duration, our experience itself persists for a matching amount of time. Foster also numbers amongst the few explicit exponents matching. As he concludes on the basis of an argument concerning the diachronic structure of auditory awareness: ‘we have to take experience to extend over a period of real time in a way which exactly matches the phenomenal period it presents’ (1991: 249).3 Having set-out the commitments of the naïve view, I now turn to a major challenge it faces.
ii. TROUBLE FOR NAÏVETÉ Car crash victims, pilots forced to eject their planes, rock climbers suffering serious falls, and other survivors of life-threatening danger reliably report that the traumatic events which they experienced appeared to last much longer than events of the same objective length in normal conditions.4 To see why such cases of ‘time seeming to slow !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! 2
For more on these themes see Phillips 2010, forthcoming. See also Dainton who, in the context of endorsing Foster’s overlap model of the diachronic structure of experience, comments that ‘even if we draw an awareness-content distinction [which Dainton ultimately rejects] it makes no sense to suppose that an act of awareness can apprehend a content of a greater temporal duration that itself’ (2000: 180). For discussion of what is fundamentally at work in Foster’s argument here see Phillips 2010. 4 See Noyes and Kletti 1976, 1977, Flaherty 1999, Carson 1999, Ursano et al. 1999 and Hancock and Weaver 2005. Such real life cases have been replicated under experimental conditions, though with obvious ethical constraints. For example, Langer et al. (1961) asked subjects to estimate a 5s interval whilst being moved towards or away from a precipice. Subjects being moved towards judged 5s over after 3.37s. Ss being moved away judged it over after 4.22s. This reveals a 20% ‘slowing of time’ in the more fear-provoking condition. For other quasirealistic studies see Falk and Bindra 1954, and Watts and Sharrock 1984. For the (similar but less dramatic) effects of mildly fear-provoking stimuli on time perception see, e.g., Noulhiane et al. 2007, Droit-Volet and Gil 2009, Wittmann et al. 2010, and Tipples 2008, 2011. 3
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down’ pose a difficulty for the naïve view, consider a simple example. A rock climber falls from a rock face and hits the ground a second later. The climber reports that his one-second fall seemed to last a great deal of time. It is tempting to think of the climber as thus misperceiving their fall in the sense of experiencing it as lasting much longer than it in fact did, for instance as taking ten seconds when it in fact took only one. If this is the right way to describe the climber’s experience, then, given the naïve matching claim above, the climber must enjoy an experience of their fall which itself lasts ten seconds. This is not incoherent, but it is surely not credible (at least in general). As we naturally imagine the case, the rock climber’s experience of their fall doesn’t continue to unfold for nine seconds after they have hit the ground. Whilst a number of possible ways of accommodating such an extended experience suggest themselves, it is implausible that in every case some such accommodation occurs. Indeed, we naturally think that the climber might be rendered unconscious the moment that they hit the ground, and yet nonetheless experience their fall much as they later report. It seems then that the naïve view cannot provide a plausible account of such experiences and so must be rejected. How might the naïve theorist respond to this line of thought? One possibility is to deny that such distortions really do occur despite subjects’ reports. This is in fact a surprisingly common view in the empirical literature. Thus, Stetson, Fiesta and Eagleman offer experimental data in support of the conclusion that ‘time-slowing is a function of recollection, not perception’ (2007: 1) and Gallistel endorses the more general anti-realist idea that ‘duration is not itself a sensible aspect of events’ but ‘exists only in recollection’ (1996: 336).5 Such views are not lightly dismissed. However, in the present context I confine myself to two brief remarks. First, Gallistel’s apparent anti-realist view that duration ‘exists only in recollection’ is clearly not an option available to the naïve theorist since it precisely abandons the first realist component of their position. Second, in motivating their hypothesis about duration distortions, Stetson et al. commit to a questionable theoretical assumption (namely, that in order for duration distortions to be perceptual our perception of duration must be a function of sensory resolution) which, in the light of the view of duration perception !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! 5
Gallistel’s view has significant precedent in the philosophical literature. It seems to be a natural consequence of the kind of scepticism about time-perception one finds in Reid (1827) and others who follow him (e.g., Prichard 1950); cf. Le Poidevin 2007: 99. However, it is not entirely clear whether Gallistel is best understood as a straight-forward anti-realist or as claiming, in an admittedly misleading fashion, that memory plays a constitutive role in conscious perceptual experience.
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proposed below, is seen to be non-mandatory.6 Rather than appeal to memory I now develop an alternative realist account of duration perception which shows how to reconcile the naïve view with traumatic duration distortions.
iii. OUR MEASURE OF PERCEIVED DURATION In developing the charge that traumatic duration distortions are a counter-example to naïve matching, the discussion of the rock climber above assumed that the climber experienced the duration of their fall as lasting a certain number of seconds. I suggest that trouble for the naïve view arises because of this assumption. If we take the fall to be experienced as having a certain objective metric duration (i.e. 10s), then there appears to be a lack of objective time in which to accommodate an experience of matching duration. It is far from obvious, however, that we do strictly experience duration in seconds, or otherwise relative to an objective, subject-independent metric. By questioning this assumption, the naïve theorist might thus hope to reconcile the duration distortions of trauma with their view. However, for this to be a satisfactory response, the naïve theorist owes us a fuller account of duration perception, and in particular of our experiences of distorted duration in trauma, freed of the objectionable assumption. Developing such an account is the goal of the remainder of this section. The most minimal account of perceived duration we might plausibly propose would involve our simply perceiving relative duration. 7 According to such a purely relative view of perceived duration, we are only ever aware of the ratios of durations of perceived events. In the simplest case both such events will occur in the specious present. Thus, we might hear two tones as lasting the same amount of time, or see one briefly presented visual stimulus as presented for twice as long as another. The relational view need not limit itself to relations between !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! 6
For an excellent discussion of Stetson et al. 2007 see Arstila 2012. Arstila defends an account of temporal distortions congenial to that defended here. A key difference is that the present account proposes a general account of distortions of perceived time in terms of the role of mental activity in timing. In contrast, Arstila apparently takes trauma to be a special case. Thus, Arstila explicitly sets aside the vast majority of research on duration estimation, preferring to explain such data in traditional internal clock terms. See §6 for discussion of internal clock models. 7 For the idea that perception of the extensive magnitudes in general is purely relative see discussion in Shepard 1978 and Sarris 2006. One reason for taking such a view is that subjects are perhaps two orders of magnitude worse at making absolute judgments compare to relative judgments of sameness or difference (Miller 1956).
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‘presently’ perceived stimuli, and there is scope (how much being an empirical question) for comparison over slightly longer periods, or relative to some abstracted standard (e.g., the average length of recent stimuli). The crucial point is that we do not strictly perceive events as having any metric duration. Such a view of duration perception would fit with a more general view of the perception of extensive magnitudes as wholly relational. For example, according to such a view of size perception, we never simply perceive the length of a stick, but rather only its length relative to the length of other objects. Again, in the simplest cases, both objects of the comparison will be objects within the present visual field, but there is scope to allow for comparisons with temporally adjacent, and ‘abstracted’ objects. A purely relational view of perceived magnitudes has consequences for hypothetical extreme cases. Thus, Shepard: Imagine a line segment that, although it does have a definite physical length (…), is somehow presented in such a way as to prevent comparison of its visual extent with any reference extent (…). Although the line could presumably still appear to be extended under such hypothetical conditions, it is doubtful whether its extent could be appreciated as a uniquely defined psychological magnitude … natural selection has favoured nervous systems that are primarily attuned to what is “out there” in the external world; and … what is out there is most easily and accurately determined by making comparisons. (1978: 463)
In the temporal case, the analogue of Shepard’s line would be a brief event with some definite objective duration somehow presented so as to prevent comparison of its duration with any reference duration. In this situation it is tempting to conclude that although the event would still appear to have what Ward (following Kant 1781/2003: A805/B833) called ‘protensity’ (1918: 119), it could not be appreciated as having any duration proper. For that comparison is needed. However, whether or not we agree with Shepherd’s view of the spatial case, it is doubtful that we can in fact imagine an analogous temporal case. The reason for this is that whilst it might be possible to eliminate all comparative temporal magnitudes in the subject’s apparent perceptual environment, the elimination of all temporal comparisons
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whatsoever would require additionally eliminating all non-perceptual mental activity. Yet, to the extent that mental activity of some kind is simply part of the condition of waking consciousness, doing so would simply render you unconscious. As a result, even in the absence of perceptual comparisons, as a condition of waking consciousness plausibly there will always be non-perceptual mental activity with temporal properties to serve as a measure of perceived duration. This suggests a natural extension to a purely relative account of perceived duration according to which as well as perceiving the relative durations of perceptual events, we are aware of their durations as measured by the non-perceptual activity that occurs between their onand offset. According to this hypothesis, we perceive more than purely relative perceptual durations, but we do not perceive duration relative to an objective, subject-independent metric, like seconds. Instead, our measure of duration is itself an aspect of our current psychological condition. (We might compare the contrast between accounts of sizeperception according to which we perceive the sizes of objects in metres and accounts on which we perceive them only relative to an aspect of our own body’s size, e.g., our effective eye height as in Wraga 1999.) The idea that we are aware of the durations of events in our environment relative to occurrences in our non-perceptual stream of consciousness can be used to make sense of what is going on in the global duration distortions of trauma consistent with the naïve view. We can begin here by turning to the anecdotal reports of subjects. Noyes and Kletti (1977) provide a rich supply, of which the following are representative.8 My mind speeded up. Time seemed drawn out. It seemed like five minutes before the car came to a stop when, in reality, it was only a matter of a few seconds. ... My mind was working rapidly and reviewed information from driver’s education that might bear on what I should do to save myself. (376) As the time in which everything happening seemed to slow down, my thoughts speeded up. (378) !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! 8
See also Noyes and Kletti 1976 and Flaherty 1999 which also makes the connection with mental activity explicit. Flaherty quotes Charles Darwin recalling a childhood fall as follows: ‘the number of thoughts which passed through my mind during this very short, but sudden and wholly unexpected fall, was astonishing’ (Darwin 1888/1959: 29; quoted in Flaherty 1999: 75).
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My thinking processes increased at an incredible rate so that my movements, in relation to them, seemed extremely slow. (378)
In each of these cases, as Noyes and Kletti bring out, a striking and evidently subjectively central aspect of the experience is that whilst, on the one hand the subject experienced time as slowed down or drawn out, on the other hand they experienced their minds or thinking processes as sped up. This correlation emerges clearly in the statistical data. Of the subjects Noyes and Kletti interviewed who believed they were about to die, 78% reported ‘altered passage of time’, (almost without exception a slowing); 68% reported ‘increased speed of thoughts’. The data support the idea that what is happening in trauma is that our awareness of the duration of the traumatic event is (at least in part) being measured relative to our non-perceptual mental activity, or what we might in a very general sense call ‘thought’. What the subjects above are reporting experiencing then is ‘time slowing down’ in virtue of an usually large amount of non-perceptual mental activity occurring within a certain objective period, much more activity than would normally occur during such a period.9 As a result, these subjects experience both an increase in their rate of mental activity in comparison to perceived environmental events (including their own bodily movements it seems), and, correlatively, an apparent slowing down of environmental events around them in comparison to their mental activity in the relevant period. In these contexts, and arguably more generally, our concurrent awareness of non-perceptual mental activity is providing our measure of perceived duration. It is a delicate question how we should distinguish between perceptual experience and what I have referred to as ‘non-perceptual mental activity’. But, however exactly we do make the distinction, it is clear that imagery and episodic memory fall on the non-perceptual side. For it is precisely an increase in the rate of activity in episodic memory that explains the phenomenon of one’s life flashing before one’s eyes in moments of fear. Thus, another subject interviewed by Noyes and Kletti reports the following. I started seeing good and bad things in my life … scenes that flashed rapidly before my eyes like lantern slides shown in rapid succession. … I !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! 9
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See also Sierra 2009: 36, Arstila 2012.
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don’t remember how many there were but, from the moment I saw the accident about to happen, it seemed like I waited forever for the impact. (1977: 377)
On the hypothesis under consideration, the apparent drawing out of time experienced by this subject is explained by the dramatic concurrent increase in episodic remembering.
iv. NAÏVETÉ OUT OF TROUBLE The hypothesis that our non-perceptual mental activity provides for us a measure of perceived duration, and that this is what explains the distortions experienced in trauma, allows the naïve theorist to resist the objection levelled above. Assuming that, in trauma, we experience duration relative to our mental activity, the rock climber’s experience of their fall is of an event which lasts the same amount of time as a certain amount of mental activity. What explains their report of time slowing down or being drawn out is that a great deal more mental activity occurs during the fall than would normally occur during a one second period. As measured by concurrent mental activity, then, the fall seems dramatically slowed: it takes place over a period during which a great deal of mental activity takes place. (Imagine, by way of analogy, that we perceive the heights of objects relative to our effective eye-height. Then, if we were shrunk like Alice in Wonderland to a fraction of our usual size, the world would seem huge in comparison.) According to naïve matching, whenever our experience presents us with an event with a certain apparent duration, our experience itself persists for a matching amount of time. In this case our experience presents us with a fall-event as apparently having the same duration as a great deal of mental activity. The experience itself must therefore actually last for a period of time during which a great deal of mental activity occurs. Yet this is quite unproblematic. For the experience can do so without continuing on after the climber has hit the ground. Nothing prevents the experience lasting just one second, so long as it is a second during which a great deal of mental activity occurs (precisely what is occurring according to the hypothesis in question). It is important to emphasise that this hypothesis allows for misperception of duration. That may not immediately be evident, because in this particular case, it is no longer obvious that there is any !
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misperception involved in the climber’s experience. The subject will likely be inaccurate in saying how many seconds their fall lasted, but this does not reflect an inaccurate percept, but rather a mistaken judgement. However, in other cases, the possibility of misperception, as opposed to mistaken judgement, remains. For instance, lightning strikes last only around 50 microseconds, yet, due to visible persistence (Coltheart 1980), the lightning appears to last for a duration similar to much longer lived events. Such comparator events may be perceptual events or they may be elements in our non-perceptual consciousness. Either way, the relative perception of the lightning’s duration will be a misperception.
v. A RELATED CHALLENGE: THE ODDBALL ILLUSION Duration distortions in trauma are not the only alleged counter-example the naïve view faces. Another case claimed to present naïve matching with a difficulty is the so-called ‘oddball effect’. In the relevant set-up, subjects have to detect and respond to a statistically unlikely stimulus embedded in a series of otherwise identical repeated stimuli. For example, subjects might have to respond to a red circle presented in the middle of a series of black circles. In a case where each black circle is presented for 1050ms with approximately similar gaps between stimuli, the red circle looks to subjects to be of the same length as the black circles when presented for only 800ms (Tse et al. 2004; for a wideranging review see Eagleman 2008). More generally, oddball stimuli of equal objective duration seem to last 20- 50% longer than the nonoddball stimuli they are presented with. According to Lee: These examples provide counterexamples to [naïve matching], provided they involve an experience lasting less time than it presents a stimulus as lasting—in other words, provided the dilation of subjective duration is not accompanied by a corresponding dilation of the objective duration of the experience.… [Yet] it would be very strange to hold that it must be the case that the subject’s experience of e.g. the oddball is objectively longer than her experience of the other stimuli, even if the stimuli themselves have the same duration. Assuming the oddball stimulus appears to last longer than it really does, if this claim were correct, it seems that the subject’s experience of each of the stimuli that occur after the oddball would have to lag behind in order to fit the longer experience of the oddball into the stream of consciousness. With
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enough oddballs we could make each experience lag behind its stimulus any amount we chose! (2009: Ch.1)
The naïve theorist has, in fact, at least two ways to respond to this objection. The first response makes no appeal to mental activity. Instead it agrees that we perceive the oddball as lasting significantly longer than the adjacent non-oddball stimuli (a matter of merely relative perception). However, it points out that neither Lee nor Tse et al. (2004) give us any reason to assume that it is the oddball that is ‘expanded’ as opposed to the adjacent non-oddball stimuli that are ‘contracted’ (a proposal defended by Pariyadath & Eagleman 2007). If the adjacent repeated stimuli are contracted, then Lee’s particular way of developing the difficulty for naïve matching will not hit the mark, since there will be no concern about how ‘to fit the longer experience’ into the stream of consciousness. The second response to the oddball objection does appeal to mental activity. According to this interpretation of the data, the oddball generates an increase in concurrent mental activity relative to which the oddball’s duration is perceived as expanded. This would make the oddball akin to a fear-inducing stimulus, and so mirror the discussion above. The suggestion need not be that the oddball activates the fear system, its mere novelty may be sufficient to boost mental activity. However, there is some empirical support for the connection between oddballs and fear. In particular, Wittmann et al. 2010 argue that ‘it is not the occurrence of a differing or oddball target stimulus per se that evokes an overestimation of duration but the specific occurrence of a looming signal that is virtually moving towards the viewer’ (Wittmann et al. 2010: 7). Wittmann et al. go on to suggest that a looming stimulus may be ‘experienced as posing a “threat”’ (ibid.: 8, citing Schiff et al. 1962; see also van Wassenhove et al. 2008). Clearly these are matters for further empirical investigation. And no doubt there are other potential concerns for the naïve view to consider, each in its own terms.10 Nonetheless, thus far, by rejecting the idea that we perceive durations relative to a subject-independent metric, and appealing to the idea that activity in our non-perceptual stream of consciousness provides for us a measure of perceived duration, we have found on the one hand no compelling reason to relinquish the naïve !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! 10
Watzl (2012) argues that so-called ‘silencing illusions’ provide a counter-example to naïve matching. I dispute this claim in my ‘Breaking the silence’ (in preparation).
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view, and on the other a possible way of unifying otherwise disparate data relating to trauma and the oddball effect. In what remains, I turn to a consideration of certain empirical data traditionally appealed to in support of internal clock models of timing. I make two suggestions. First, that such data may in fact provide further evidence of the role of mental activity in our awareness of duration. Second, that the mental activity hypothesis is explanatorily superior to a traditional internal clock model in accounting for the adaptive value of time distortions.
vi. FEAR, FEVER, PHARMACOLOGY AND FLICKER There are two main strands to the empirical literature on duration perception. One is largely concerned with dual-task paradigms, findings from which motivate so-called attentional approaches to timing. I discuss these in relation to the present hypothesis elsewhere. 11 The second strand, which I pursue in what follows, concerns data usually taken to support internal clock models of timing. This body of data relates to the effects of various interventions on duration judgments. In particular, the effects of emotional stimuli, of raising and lowering body temperature, of dopaminergic drugs, and of exposing subjects to repetitive visual or auditory simulation. In short: fear, fever, pharmacology and flicker. The basic effect of fear on timing has already been noted. In general, fear increases the apparent length of an interval or stimulus relative to a control.12 The effect of body-temperature on the apparent passage of time was the focus of the earliest studies in support of an internal clock model (François 1927; Hoagland 1933). Experimenting on his fevered wife, Hoagland found that increases in body temperature slowed her sense of the passage of time: events seemed to take longer than they usually did. The subsequent literature (reviewed in Wearden and PentonVoak 1995) finds the same basic effect: increased body temperature leads to increased time estimation; decreased body temperature leads to
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See Phillips 2012 where I argue that ubiquitous but obscure explanatory appeals to ‘attention to the passage of time’ are best understood in terms of the role of mental activity in timing. 12 For the complex effects of other emotions see, e.g., Droit-Volet and Meck 2007.
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decreased time estimation.13 In short: external events seem slower when you’re hot, and faster when you’re cold. The standard finding from animal and human drug studies is that dopamine agonists (e.g., cocaine, methamphetamine, and caffeine) lead to intervals being over-estimated, whereas dopamine antagonists (e.g., anti-psychotics like haloperidol) lead to intervals being under-estimated. 14 Finally, an important psychophysical technique in the timing literature involves preceding or accompanying stimuli with a train of repetitive stimulation (periodic clicks or flashes). Such stimuli are then perceived as if their duration is increased compared to a silent or white-noise control (Treisman et al. 1990 and Penton-Voak et al. 1996). Such data have been a central source of support for internal clock models of time perception, and such models remain highly influential in large part because of their capacity to provide a simple and unified explanation of the effects of these various interventions on timing.15 The core idea behind an internal clock model is that each of us is equipped with an internal clock or pacemaker whose function is to produce regular or random pulses. 16 The perceived duration of an event or interval is then modelled as an increasing function of the number of pulses accumulated during the event or interval. On a very simple model we can think of judgments of metric duration (e.g., ‘that event lasted one second’) as based on a comparison between the number of accumulated pulses and a reference memory which represents how many pulses are normally associated with a one second period. (See Figure 1 below.)
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Unsurprisingly, these effects only obtain within limits, e.g., they break down with extreme fever, and are subject to various caveats, e.g., cold shock has the same effect as raising body temperature (Wearden and Penton-Voak 1995: 137; see Fox et al. 1967 and Lockhart 1967). 14 See, e.g., Meck 1996, Meck 2005, Coull et al. 2011, Maricq et al. 1981, Matell et al. 2004, MacDonald and Meck 2005, Drew et al. 2003, Buhusi and Meck 2002, Cevik 2003. 15 As Droit-Volet and Gil put it, ‘the internal clock model remains the dominant theoretical model of time because it permits an excellent description of a wide range of experimental results across many paradigms’ (2009: 1944). 16 Early clock models were developed in Creelman 1962 and Treisman 1963. The most influential model is scalar timing (or expectancy) theory (SET) due to Gibbon (1977), developed in Gibbon et al. 1984, and applied to human timing in, e.g., Wearden 1991. For reviews of the development and controversies surrounding such models see, for instance, Wearden 2001 and 2003.
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Figure 1. A Simplified Internal Clock Model of Timing. Cf. Gibbon et al. 1984.
The internal clock model has a straight-forward explanation of the effects of the varied interventions noted above: such interventions directly modulate the rate of the pacemaker, and so lead to a greater (or fewer) number of pulses being accumulated during the relevant interval. Thus whether you frighten someone, increase their body temperature, give them a dopamine agonist, or stimulate them with repetitive clicks or lights, you affect their time perception in the same basic way, by increasing the rate of their pacemaker and thereby causing them to overestimate how much time has passed. In this way, the internal clock model is supposed to unify a disparate set of data, explaining why all these heterogeneous interventions have an effect on duration judgements by affecting the number of pulses accumulated. Might the hypothesis that mental activity provides a measure of perceived duration be able to explain the effects just described? It could insofar as fear, fever, pharmacology and flicker modulate mental activity in ways which parallel their alleged effects on a hypothetical internal clock. Establishing that this is the case is of course a matter for substantial empirical investigation, but I do want to suggest that the !
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hypothesis is worthy of serious consideration. Consider for instance what we know about the effects of body temperature on cognition: raising body temperature increases alertness and enhances cognitive function on a range of likely measures (e.g., Wright et al. 2002). Likewise, it hardly needs saying that dopamine agonists such as amphetamines increase alertness and heighten cognitive function (e.g., Ballas et al. 2009) whereas anti-psychotics reduce alertness, ‘blunting cognition’ (e.g., Nasrallah and Tandon 2009). More intriguingly, Jones et al. (2011), found that ‘response times on [an] arithmetic task were significantly reduced by [repetitive] clicks’ in contrast to a white noise control condition which also has no effect on timing.17 Collectively, such findings should encourage us to take seriously the hypothesis that variation in duration judgments due to a wide range of interventions may be the result of variation in concurrent mental activity relative to which we measure the durations of environmental events. The empirical investigation of this hypothesis presents a large empirical challenge. For whilst it is undoubtedly possible to measure the effects of a given intervention using a standardized cognitive test (e.g., a working memory task such as a basic arithmetic test or the Digit Symbol Substitution Test standardly used to diagnose concussion, or a vigilance test such as the Psychomotor Vigilance Task), we cannot straightforwardly associate increased performance on such measures with greater speed of mental activity. Certainly, there is an intuitive connection.18 But it is plausible that in some situations, greater speed of mental activity may be detrimental to cognitive performance, for example during episodes of extreme anxiety or mania. The empirical challenge then is to draw on subjective reports, objective behavioural measures and possibly also physiological measures (e.g., activity in the frontal lobes, heart rate, skin conductance, and pupil dilation) to establish the exact relationship between rate of mental activity and judgments of elapsed time, and not simply to rely on standardized cognitive test scores as proxies for mental activity. By way of further motivating that inquiry, I want to end by advertising a clear explanatory advantage of a mental activity based !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! 17
Jones et al. also found improvements in a traditional working memory paradigm in the clickcondition. 18 For example, in a classic study, Kleitman explicitly connects increases in body temperature with increase in the ‘speed of thinking’ on assumption that reaction time correlates with speed of thought (1934: 501).
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approach over a traditional internal clock account. The advantage arises in explaining the adaptive value of temporal distortions.19 Theorists in the time perception literature often claim that temporal distortions are adaptive. Thus, commenting on evidence which shows that subjects over-estimate time in a stressful situation, 20 Hancock and Weaver comment, ’Phenomenologically, time slowed down in the stressful condition…. this represents an adaptive and appropriate response‘ (2005: 198).21 Internal clock theorists offer an explanation along the following lines: when a subject is confronted with a threatening event, the internal clock runs faster under the influence of dopamine, and the preparation for action is quicker. By modifying the perception of time, the internal clock ensures the survival of the organism in urgent situations. (Droit-Volet and Gil 2009: 1946)
The explanation appears to be the following. Threat-evoked fear leads to a spike in dopamine levels, which in turn increases the rate of the internal clock. This is the basis of subjective time expansion, and this is said to mean that subjects are more quickly able to prepare for action. As one neurophilosophy blog put it, ‘In such a situation, an illusion of time dilation could facilitate an effective escape’.22 However, on reflection, there is something very puzzling about this explanation. Imagine that you are a cave man or woman on the veldt. You spot a sabre-tooth tiger heading your way. Then suddenly the world around you seems to slow down and the tiger appears to be running more slowly. How is this helpful? The tiger is not actually running any more slowly. And the illusion of time being drawn out gives you no extra seconds to run away from it. We get a much more satisfactory explanation of what is going on if we consider how things look on a mental activity picture. Here the effect of the fear-based dopamine spike is to speed mental activity. That, in and of itself, is an adaptive response. Assuming your mental activity remains ordered and under your control (e.g., you do not panic or become manic), its increased rate means that in the same limited time !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! 19
One might also note another explanatory advantage, namely that whereas we have only indirect evidence for positing an internal clock, it is quite obvious that mental activity exists. 20 Namely, Langer et al. 1961 mentioned above. 21 Cf. Carson 1999, Tipples 2011. 22 URL = <http://scienceblogs.com/neurophilosophy/2010/01/23/is-time-dilated-during-athreatening-situation/>. Last accessed on 22 March 2013.
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span you are more quickly able to plan action. On the veldt you can more quickly think where to run or hide from the tiger, or how to scare it off.23 The fact oneâ&#x20AC;&#x2122;s perceived environment appears slowed is a result of this increase in mental activity, and in that derivative sense (and that sense alone) temporal expansion is adaptive.
vii. CONCLUSION The dramatic duration distortions experienced during trauma have often been thought to reveal something about the nature of our duration perception in general. Rather than forcing us to give up our naĂŻve commitments concerning duration perception, I have argued that what they suggest is that we perceive duration in part relative to concurrent non-perceptual mental activity. In addition to according well with the anecdotal reports of subjects, such a hypothesis may account for the effects of a range of interventions on timing, and make sense of the adaptive value (such as it is) of duration distortions.
University College London Gower Street London WC1E 6BT United Kingdom i.phillips@ucl.ac.uk
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Tellingly, many anecdotal reports of subjects in life-threatening situations attribute their survival to their amazing capacities to think what to do or to recall relevant information in a very short space of time.
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