Abstract
Perceived time undergoes distortions when we prepare and perform movements, showing compression and/or expansion for visual, tactile and auditory stimuli. However, the actual motor system contribution to these time distortions is far from clear. In this study we investigated visual time perception during preparation of isometric contractions and real movements of the hand in two different directions (right/left). Comparable modulations of visual event-timing are found in the isometric and in the movement condition, excluding explanations based on movement-induced sensory masking or attenuation. Most importantly, and surprisingly, visual time depends on the movement direction, being expanded for hand movements pointing away from the body and compressed in the other direction. Furthermore, the effect of movement direction is not constant, but rather undergoes non-monotonic modulations in the brief moments preceding movement initiation. Our findings indicate that time distortions are strongly linked to the motor system, and they may be unavoidable consequences of the mechanisms subserving sensory-motor integration.
Highlights
Action-related temporal distortions are not restricted to the sensory channel that is directly linked to the relevant motor system
This study addresses this hypothesis by investigating the time course of visual temporal distortions during preparation for hand movements and its specificity for different movement directions
A two-way repeated-measures ANOVA on the Point of Subjective Equality (PSE) with direction and latency (−0.175, −0.125, −0.075, −0.025, +0 .025 s) as within-subject factors shows that temporal intervals are perceived as shorter for the left compared to the right direction (F(1,4) = 63.335, p = 0.001; main effect of factor direction) with no systematic effect of stimulus latency (F(4,16) = 1.795, p = 0.179; main effect of factor latency)
Summary
Action-related temporal distortions are not restricted to the sensory channel that is directly linked to the relevant motor system (i.e., vision for the oculomotor system or touch for the haptic system). On the contrary, has been observed for visual stimuli presented during preparation for reaching movements[13] and the effect is modulated by the degree of motor preparation. Most interestingly, it is accompanied–and possibly explained-by changes in visual information processing, as indicated by the concomitant improvement in detection performance for rapidly displayed visual targets[13]. If time distortions are driven by early motor signals during the preparatory stage we might expect modulations by specific features of the planned movements, even before movements are implemented This study addresses this hypothesis by investigating the time course of visual temporal distortions during preparation for hand movements and its specificity for different movement directions (right/left). To isolate the contribution of motor planning processes and rule out any confound due to sensory masking or spatial effects induced by hand displacement we tested both an isometric contraction and a real movement condition
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