Speed Changes and Time Perception 1 Time Winding Down: How Do Changes in Speed Affect the Perception of Duration?

Six experiments investigated how changes in stimulus speed influence subjective duration. Participants saw rotating or translating shapes in three conditions: constant speed, accelerating motion, and decelerating motion. The distance moved and average speed were the same in all three conditions. In temporal judgment tasks, the constant-speed objects seemed to last longer than the decelerating ones, which in turn seemed to last longer than the accelerating stimuli. In temporal reproduction tasks, the difference between accelerating and decelerating stimuli disappeared; furthermore, watching an accelerating shape lengthened the apparent duration of the subsequent (static) display. These results (a) suggest that temporal judgment and reproduction can dissociate for moving stimuli because the stimulus influences the apparent duration of the subsequent interval, and (b) constrain theories of time perception, including those which emphasize memory storage, those which emphasize the existence of a pacemaker-accumulator timing system, and those which emphasize the division of attention between temporal and non-temporal information processing. Speed changes and time perception 3 Time winding down: How do changes in speed affect the perception of duration? Suppose that you are standing on the platform of a railway station. Whilst waiting for your train you watch several others move past: One glides through the station at a steady pace; a second pulls out of the platform opposite and gathers speed before it disappears around the corner; and a third hurtles out of a tunnel and slows to a halt to pick up passengers. Assuming that all three trains are visible for the same length of time, will these three events all seem to have equal duration? Or will the nature of the movement affect your perception of time? Several investigators have examined the effects of stimulus speed on time perception. The most widely-repeated finding is that moving stimuli seem to last longer than static ones (e.g., S. W. Brown, 1995; Kanai, Paffen, Hogendoorn, & Verstraten, 2006; Lhamon & Goldstone, 1975), and that apparent duration increases with increasing stimulus speed (e.g., Beckmann & Young, 2009; S. W. Brown, 1995; Kaneko & Murakami, 2009; Leiser, Stern, & Meyer, 1991). Some caution is needed before accepting the generality of these conclusions because the results are context-dependent: a stationary oddball shown in a train of moving stimuli will have longer subjective duration (Tse, Intriligator, Rivest, & Cavanagh, 2004). The effects of stimulus speed on subjective duration have implications for any model of time perception. Theories of time perception can be grouped into two broad classes (Lejeune, 1998). The first class assumes that duration is a by-product of non-temporal information processing; there is no specialized “timer” for measuring duration. For example, Ornstein (1969) argued that perceived duration depends upon the space needed to store the stimulus in memory, and others have stressed that time perception depends on the number of changes taking place during an interval (e.g., Block & Reed, 1978; Poynter, 1983). These storageor change-based models have typically been applied to retrospective time judgments – where the participant does not know in advance that they will be asked for a time estimate – but they have also been related to the effects of stimulus motion on time perception in prospective tasks, where the observer knows that a time judgment will be required: More complex motion patterns are taken to lengthen apparent duration (Aubry, Guillaume, Mogicato, Bergeret, & Celsis, 2008) and faster speeds are taken to entail greater positional change and, accordingly, longer subjective time (S. W. Brown, 1995; Poynter, 1989). The second class of models assumes a specialized mechanism for measuring time, based upon some kind of accumulation or counting process (e.g., Gibbon, Church, & Meck, 1984; Rammsayer & Ulrich, 2001; Treisman, 1963; Treisman, Faulkner, Naish, & Brogan, 1990). There is usually taken to be an internal pacemaker or oscillator which emits pulses that are accumulated until stimulus offset, at which point the number of counts in the accumulator provides the measure of Speed changes and time perception 4 duration. A subset of these pacemaker models include the idea that attention must be divided between temporal processing and non-temporal processing, such that directing attention away from the timer reduces pulse accumulation and shortens subjective duration (e.g., Zakay & Block, 1997). Stimulus speed has been argued to affect the pacemaker, with faster speeds producing higher accumulation rates and longer subjective time (Kaneko & Murakami, 2009). The current work builds on previous investigations of the effects of movement on time perception by asking, for the first time: how do changes in speed affect the perception of duration? That is, if a moving stimulus remains visible for a fixed time, and travels a fixed distance, does its apparent duration depend on whether it accelerates, decelerates, or moves at a constant speed? Existing models do not generate clear predictions regarding the effect of changes to stimulus speed on subjective duration because the relationship between stimulus movement and the relevant theoretical constructs is rather under-specified. For example, does storage size depend purely on distance moved – in which case accelerating, decelerating, and constant-speed stimuli will have the same subjective duration – or do changes in speed entail an additional complexity, such that constant-speed stimuli seem shorter than accelerating and decelerating objects? Similarly, pacemaker-accumulator models do not provide strong predictions as they depend on the assumed relationship between stimulus speed and pacemaker rate. The aim of the current experiments is therefore to establish the phenomenology of the effects of changes in speed on subjective duration. These effects will not allow us to choose between competing models of time perception, but they will provide an important constraint on how these theoretical positions accommodate the effects of stimulus motion on subjective time.