Processing of collision information in the human superior colliculus
23.501, Saturday, May 11, 8:30 am - 12:30 pm, Vista Ballroom
Peng Zhang1, Sheng He1,2; 1State Key Lab of Cognitive Sciences, Institute of Biophysics, Chinese Academy of Sciences, 2Department of Psychology, University of Minnesota
Detecting looming objects with imminent collision is crucial for survival. The involvement of the human subcortical visual pathway in processing such threatening information remains unclear. Using fMRI, we investigated the functional properties of the superior colliculus (SC) in responding to potential collision information, with or without attention to or consciousness of the colliding object. In experiment 1, subjects judged whether a looming object was on a collision course with the subjects head. BOLD response of the SC was stronger when the looming stimulus was on vs. off a colliding course. SC response to collision was also lateralized - stronger when the collision stimulus originated from the contralateral rather than ipsilateral visual field of the SC; and stronger when the would-be point of collision was contralateral than ipsilateral to the SC. In experiment 2, subjects attention was directed to a demanding central fixation task, and consequently no reliable BOLD responses were found in the SC to the looming event, suggesting that some level of attention is needed for the SC to process the collision information. In experiment 3, awareness to the collision object was greatly reduced by presenting the looming stimulus briefly (233 ms) and together with nine other near miss distractors. Results showed stronger SC activities to looming targets on than off the collision course, even when subjects were unable to correctly detect the collision event. These results suggest that SC plays a critical and spatially specific role in the processing of collision information, and this neural process in SC is dependent on the availability of attention but not explicit awareness of the threatening information.