Perception: Transient Disruptions to Neural Space–Time

Perisaccadic encoding of temporal information in macaque area V4

The accurate processing of temporal information is of critical importance in everyday life. Yet, psychophysical studies in humans have shown that the perception of time is distorted around saccadic eye movements. The neural correlates of this misperception are still poorly understood. Behavioral and neural evidence suggest that it is tightly linked to other known perisaccadic modulations of visual perception. To further our understanding of how temporal processing is affected by saccades, we studied the representations of brief visual time intervals during fixation and saccades in area V4 of two awake macaques. We presented random sequences of vertical bar stimuli and extracted neural responses to double-pulse stimulation at varying interstimulus intervals. Our results show that temporal information about very brief intervals of as brief as 20 ms is reliably represented in the multiunit activity in area V4. Response latencies were not systematically modulated by the saccade. However, a general increase in perisaccadic activity altered the ratio of response amplitudes within stimulus pairs compared with fixation. In line with previous studies showing that the perception of brief time intervals is partly based on response levels, this may be seen as a possible correlate of the perisaccadic misperception of time.NEW & NOTEWORTHY We investigated for the first time how temporal information on very brief timescales is represented in area V4 around the time of saccadic eye movements. Overall, the responses showed an unexpectedly precise representation of time intervals. Our finding of a perisaccadic modulation of relative response amplitudes introduces a new possible correlate of saccade-related perceptual distortions of time.

Intended outcome expands in time

Intentional agents desire specific outcomes and perform actions to obtain those outcomes. However, whether getting such desired (intended) outcomes change our subjective experience of the duration of that outcome is unknown. Using a temporal bisection task, we investigated the changes in temporal perception of the outcome as a function of whether it was intended or not. Before each trial, participants intended to see one of two possible outcomes but received the intended outcome only in half of the trials. Results showed that intended outcomes were perceived as longer than unintended outcomes. Interestingly, this temporal expansion was present only when the intended outcome appeared after short action-outcome delays (250 ms-Exp 1 and 500 ms-Exp 2), but not when it appeared after long action-outcome delay (1000 ms-Exp 3). The effect was absent when participants did not intend and performed instruction-based action (Exp 4). Finally, Exp 5 (verbal estimation task) revealed that intention induced temporal expansion occurs via altering the gating or switch mechanism and not the pacemaker speed. Results are explained based on intention-induced pre-activation resulting in extended temporal experience. Our study not only suggests inclusion of intention as a potential factor influencing time perception but also indicates a close link between intentional binding and the intention induced temporal expansion of its outcome.

Apparent time interval of visual stimuli is compressed during fast hand movement

The influence of body movements on visual time perception is receiving increased attention. Past studies showed apparent expansion of visual time before and after the execution of hand movements and apparent compression of visual time during the execution of eye movements. Here we examined whether the estimation of sub-second time intervals between visual events is expanded, compressed, or unaffected during the execution of hand movements. The results show that hand movements, at least the fast ones, reduced the apparent time interval between visual events. A control experiment indicated that the apparent time compression was not produced by the participants’ involuntary eye movements during the hand movements. These results, together with earlier findings, suggest hand movement can change apparent visual time either in a compressive way or in an expansive way, depending on the relative timing between the hand movement and visual stimulus.

Reduction of stimulus visibility compresses apparent time intervals

The neural mechanisms underlying visual estimation of subsecond durations remain unknown, but perisaccadic underestimation of interflash intervals may provide a clue as to the nature of these mechanisms. Here we found that simply reducing the flash visibility, particularly the visibility of transient signals, induced similar time underestimation by human observers. Our results suggest that weak transient responses fail to trigger the proper detection of temporal asynchrony, leading to increased perception of simultaneity and apparent time compression.