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 mechanisms responsible for processing the impending collision of a moving object towards a stationary observer. After discussing TTC processing in the invertebrate visual system, we describe our own work involving neurons in the pigeon nucleus rotundus that respond exclusively to visual information relating to objects that are approaching on a direct collision course, but not to visual information simulating observer's movement towards those same stationary objects. Based on the recorded neuronal responses to various manipulations of the stimuli, we classified these looming sensitive neurons into three different types of looming detectors based on the temporal differences in neuronal response relative to the moment of collision. We also described quantitative models for these looming detectors as a way of explaining their physiological response properties.