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Jac Billington, John Wann, David Field, Richard Wilkie; Sub-cortical responses to looming objects: An fMRI study of human interception of footballs. Journal of Vision 2009;9(8):1134. doi: 10.1167/9.8.1134.
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© ARVO (1962-2015); The Authors (2016-present)
Detecting the time to collision (TTC) of an approaching object is imperative to species' survival. Cells in the pigeon nucleus rotundus have been found to respond to high rates of looming. This would hint that a similar function might be found in sub-cortical areas of primates, such as the thalamic nuclei and superior colliculus (SC). We examined whether an equivalent response to looming stimuli would be found in the human SC using fMRI. Within a Siemens 3T scanner we presented virtual footballs in five conditions: a fast ball, which approached the viewer and disappeared when TTC = 0.33s; a standard ball which disappeared at TTC = 1s; a large ball (TTC = 1s) but which matched the fast ball for final optic size. Two control conditions presented a reverse ball, which matched the speed of the fast ball but moved away from the viewer and a static ball which faded in over a matched period. Participants (n = 14) were required to press a button when the ball would arrive (TTC = 0), reach a distal location or reach full luminance in the control conditions. Percent signal change in SC was significantly higher for the fast ball compared to all other conditions. The large, reverse and static balls, however, resulted in higher signal change values than the standard ball suggesting that a proportion of the SC activation was associated with lower level visual effects. A second experiment used simple dot ball stimuli to balance for low level visual effects. SC activity for fast balls was higher than for standard speed balls and marginally higher than balls matched in terms of local motion and luminance, but without the looming signals. Together these findings suggest that a subset of cells in the SC respond to looming signals signifying an approaching object.
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