Responses to Optical Looming in the Retinal Center and Periphery

Stoffregen (1985, 1986) found that the periphery of the retina is insensitive to radially structured optic flow specifying postural sway. This raised the issue of whether the retinal periphery is sensitive to radially structured flow per se, that is, to radial flow specifying events other than postural sway. In the experiment discussed herein we addressed this question in the context of optical looming. Computer-generated optical displays were presented to the retinal center or periphery of standing participants, who were required to dodge out of the path of the depicted object at the last moment before impact. Depicted trajectories were slightly eccentric, requiring participants to employ a directional response. Results showed that the trajectory and time-to-contact of the simulated object strongly influenced responses for peripheral as well as central looms. In general, responses to peripheral looms closely matched those to central looms. These findings indicate that the periphery of the retina is sensitive to optically specified time-to-contact, despite the fact that such information is carried in radially structured flow patterns. We argue that impending collision and postural sway can be distin- guished on the basis of dynamics that are characteristic of each event.