CHAPTER 2: The Biological Bases of Time-to-collision Computation

We begin the chapter by arguing that there may be several neural mechanisms that have evolved for computing time-to-collision (TTC) information as a way of controlling different classes of action. We then focus on single unit mecha-nisms responsible for processing the impending collision of a moving object towards a stationary observer. After discussing TTC processing in the inverte-brate visual system, we describe our own work involving neurons in the pigeon nucleus rotundus that respond exclusively to visual information relating to ob-jects that are approaching on a direct collision course, but not to visual informa-tion simulating movement towards those same stationary objects. Based on the recorded neuronal responses to various manipulations of the stimuli, we classi-fied these looming sensitive neurons into three different types of looming detec-tors based on the temporal differences in neuronal responding relative to the moment of collision. We also described quantitative models for these looming detectors as a way of explaining their physiological response properties