Abstract
Accurate estimates of the time-to-contact (TTC) of approaching objects are crucial for survival. We used an ecologically valid driving simulation to compare and contrast the neural substrates of egocentric (head-on approach) and allocentric (lateral approach) TTC tasks in a fully factorial, event-related fMRI design. Compared to colour control tasks, both egocentric and allocentric TTC tasks activated left ventral premotor cortex/frontal operculum and inferior parietal cortex, the same areas that have previously been implicated in temporal attentional orienting. Despite differences in visual and cognitive demands, both TTC and temporal orienting paradigms encourage the use of temporally predictive information to guide behaviour, suggesting these areas may form a core network for temporal prediction. We also demonstrated that the temporal derivative of the perceptual index tau (tau-dot) held predictive value for making collision judgements and varied inversely with activity in primary visual cortex (V1). Specifically, V1 activity increased with the increasing likelihood of reporting a collision, suggesting top–down attentional modulation of early visual processing areas as a function of subjective collision. Finally, egocentric viewpoints provoked a response bias for reporting collisions, rather than no-collisions, reflecting increased caution for head-on approaches. Associated increases in SMA activity suggest motor preparation mechanisms were engaged, despite the perceptual nature of the task.
Highlights
Accurate estimates of the time-to-contact (TTC) of approaching objects are used effortlessly in our everyday lives to guide future motor behaviour
Event-related fMRI data showed selective activation of left pars opercularis of the inferior frontal lobe and the supramarginal gyrus of left inferior parietal cortex during TTC tasks (Figure 3B)
Based on the anatomical and functional correspondence between these two paradigms, we suggest that left ventral premotor and parietal cortices are critically involved in temporal prediction
Summary
Accurate estimates of the time-to-contact (TTC) of approaching objects are used effortlessly in our everyday lives to guide future motor behaviour. Tau is perceived directly from the changing visual properties of the stimulus, the ratio between image size and its rate of change This ratio specifies the time remaining before contact (i.e. TTC), one oft-criticised feature is that it does not allow for changes in velocity. The prospective nature of this information allows subjects to modify their current behaviour, if necessary, in order to avoid collision (e.g. brake harder) It was originally suggested (Lee, 1976) that subjects control braking by actively maintaining a constant tau-dot value during the approach, the evidence for a constant tau-dot braking strategy is conflicting and unconvincing Results shows that tau-dot information is perceived passively from changing visual properties and informs about the likelihood of collision, which allows for dynamic adjustments in braking behaviour so as to avoid collision (Bootsma and Craig, 2003; Yilmaz and Warren, 1995)
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