Interceptive action: What's time-to-contact got to do with it?

Abstract The time remaining before an object arrives somewhere — its time-to-contact (TTC) with that place — is a quantity could be used to control the timing of interceptive and evasive actions directed at that object. This potential use for TTC information is the primary motivation for studying how people and animals perceive it. However, studies of interceptive actions and the role TTC information might play in controlling them have been very limited until recently — studies of the perceptual process of TTC estimation have been more popular. Unfortunately, TTC perception depends upon the task being performed and it seems impossible to understand TTC perception without understanding interceptive tasks. This chapter argues this case and discusses recent experiments that have attempted to determine how performance of interceptive actions-particularly their timing-depends upon task variables including the speed of the target, the distance to be moved to intercept it, the viewing time, the size of the target and of the intercepting manipulandum. Results demonstrate that the duration and velocity of interceptive movements are systematically and consistently affected by all these variables. The relationship between movement duration and the task variables derived from experimental results is interpreted as an empirical reflection of the ‘rule’ used by the central nervous system to preprogram movement duration. The role of TTC in the programming and initiation of interceptive movements is explicated.