Increasing Velocity Postpones Responses Compared to Decreasing Distance with Time to Collision being Equivalent: Behavioural and Neural Evidence
16.436, Friday, May 10, 5:30 - 8:00 pm, Orchid Ballroom
You Li1, Pengfei Wang1, Xiaozhe Peng1, Qi Chen1; 1Department of Psychology, South China Normal University
Spatial and temporal information must be integrated to predict the potential collision of two moving objects. It has been known that left inferior parietal cortex and bilateral sensorimotor cortex are involved in the judgments of time-to-collision (TTC) (Assmus et al., 2003, 2005; Field & Wann, 2005). In the present fMRI study, we aimed at investigating the potentially different contributions of the velocity and the distance dimension to the TTC judgments. The visual stimuli included one horizontally moving ball and one vertically moving ball. At the start of each trial, the horizontal ball started moving, and the participants were required to press a button to initiate the moving of the vertical ball at the most appropriate time so that the vertical ball could precisely hit the horizontal ball. We adopted another high-level control task in which the same set of stimuli was used and the participants were required to judgment the luminance change of the targets. More importantly, the distance and the velocity of the horizontal ball were parametrically varied. With the same four levels of time-to-collision (TTC), we either kept the distance constant and increased the velocity, or we kept the velocity constant and decreased the distance. Behavioral results showed that TTC judgment task performance significantly varied as a function of TTC. Moreover, with the velocity increasing, participants were more inclined to respond behind the theoretical time, compared with the distance-decreasing conditions. Imaging results showed that, the lingual gyrus, precuneus, and right middle frontal gyrus was specifically involved in the velocity-increasing conditions. More interestingly, lingual gyrus showed a parametric modulation effect both when velocity increased and when distance increased. Taken together, we showed that the two dimensions contributed differentially to TTC judgments at both the behavioral and the neural levels.