Human time perception and its illusions

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Why does a clock sometimes appear stopped? Is it possible to perceive the world in slow motion during a car accident? Can action and effect be reversed? Time perception is surprisingly prone to measurable distortions and illusions. The past few years have introduced remarkable progress in identifying and quantifying temporal illusions of duration, temporal order, and simultaneity. For example, perceived durations can be distorted by saccades, by an oddball in a sequence, or by stimulus complexity or magnitude. Temporal order judgments of actions and sensations can be reversed by the exposure to delayed motor consequences, and simultaneity judgments can be manipulated by repeated exposure to nonsimultaneous stimuli. The confederacy of recently discovered illusions points to the underlying neural mechanisms of time perception.

Introduction

The visual system brags a long history of parlaying illusions into an understanding of the neurobiology [1], but only recently has the study of temporal illusions begun to blossom. New illusions of duration, order, and simultaneity illustrate that temporal introspection can often be a poor guide to the timing of physical events in the world. Temporal judgments are constructions of the brain, and, as we will see below, surprisingly easy to manipulate experimentally [2].

Time perception is a term that encompasses many scales. For the purpose of this review, we will address only illusions of time perception at the ‘automatic’ or ‘direct sensation’ time scales  that is, subsecond timing. Timings of longer scales, such as seconds, minutes, and months, are categorized as ‘cognitive’ and appear to be underpinned by entirely different neural mechanisms [3, 4, 5, 6].

Section snippets

Short interval durations

Duration judgments at short intervals are subject to several types of illusions. Here is a do-it-yourself demonstration to set the stage: look at your own eyes in a mirror and move your point of focus back and forth so that you are looking at your right eye, then at your left eye, and back again. Your eyes take tens of milliseconds to move ballistically from one position to the other  but here is the mystery: you never see your own eyes move. What happens to the gaps in time while your eyes are

Predictability modulates duration

The examples above appear to be related to low-level visual processes, but the story of subjective duration grows more interesting. When a stimulus is shown repeatedly, the first appearance is judged to have a longer duration than successive stimuli [19••, 20•, 21, 22]. Similarly, an ‘oddball’ stimulus in a repeated series will also be judged to have lasted longer than others of equal physical duration (Figure 1b) [19••, 23, 24, 25]. These dilations of perceived duration have been called a

Temporal order judgments dynamically recalibrate

A challenge for the brain is that afferent signals from different sensory modalities are processed at different speeds. When receiving signals from several modalities, how does the brain determine the timing correspondences? The answer seems to be that the brain dynamically recalibrates its expectations.

In 2002, Haggard and colleagues noticed that when a subject made a motor act (such as a button press), subsequent events (such as a beep 250 ms later) appeared to be ‘pulled’ slightly closer in

Is time one thing?

An open question is whether subjective time is a unitary phenomenon, or instead whether it is underpinned by separate neural mechanisms that usually work in concert but can be dissociated under the right circumstances. In other words, when one temporal judgment changes, do the others necessarily follow suit? We give three examples that indicate the answer is ‘no’.

First, returning to the Morrone et al. [8••] finding of duration compression around the time of a saccade (Figure 1a), can one assume

Current models and their discontents

The most traditional model proposed to account for interval passage over short time scales is a simple ‘counter’ model, in which internal pulses are collected up and integrated during the presence of a stimulus [46, 47]. This is thought to account for distortions in the following way: if we imagine that the brain has access to the roughly constant rate of its own information processing (say, one bit of internal information processed is interpreted as one unit of objective time having passed),

Conclusions

The recent renaissance of temporal illusions is ripe to trigger a crossdisciplinary approach, establishing a fertile middle ground in which to combine experimental techniques employing electrophysiology, psychophysics, EEG, fMRI, and computational modeling. Mechanisms are often exposed by their stresses and strains, and the hope is that these illusions will light the way to understanding general outstanding questions of time perception: how are the signals entering various brain regions at

References and recommended reading

Papers of particular interest, published within the period of review, have been highlighted as:

  • • of special interest

  • •• of outstanding interest

Acknowledgement

This work is supported by NIH grant R01 NS053960 (DME).

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