Yarrow, Kielan Nicholas; (2003) Temporal illusions subsequent to movement. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

When saccadic eye movements are made to a silently ticking clock, observers sometimes think that the second hand takes longer than normal to move to its next position. For a short period, the second hand appears to have stopped; then, suddenly, it ticks on. This phenomenon is of intuitive interest as an experience that many people recognise, and formed the starting point of the research described here. A comparison methodology was employed in which subjects judged the perceived duration of a visual stimulus relative to that of subsequent stimuli. The duration of the first stimulus varied across trials, permitting the derivation of a matched time at which subjects felt the stimuli to be of equal duration. When the first stimulus was fixated immediately after a saccade, lower matched times were obtained relative to constant fixation conditions, indicating that subjective time had been stretched out. This effect is termed saccadic chronostasis. The methodology permitted accurate quantification of saccadic chronostasis under various task conditions. Manipulations explored include movement size, movement type (saccades of various types, hand/arm movements), the nature of the stimulus that is to be judged and its relationship to other perceptual objects. Key results include the illusion's dependency upon both saccade size and the continuity of certain components of the visual scene. Similarities and important differences emerged when the paradigm was extended to arm movements (manual chronostasis). Chronostasis offers a novel insight into the integration of action and perception, with implications for theories of perceptual continuity across movements. It is an illusion of time, and must be dealt with by theories that seek to explain temporal perception, but also has more general relevance when considering the manner in which conscious experience emerges from a sequence of sensory events. These issues inform an initial characterisation of the effect.

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