Perceiving time to collision activates sensorimotor cortex

Field, D.T. & Wann, J.P. (2005)                 
Current Biology

The survival of many animals hinges upon their ability to avoid collisions with other animals or objects, or to precisely control the timing of collisions. Optical expansion provides a compelling impression of object approach and in principle can provide the basis for judgments of time-to-collision (TTC)[1]. It has been demonstrated that pigeons [2] and houseflies [3] have neural systems that can initiate rapid co-ordinated actions on the basis of optic expansion. In the case of humans, the linkage between judgments of TTC and co-ordinated action has not been established at a cortical level. Using fMRI we identified areas of superior parietal and motor cortex, which are selectively active during perceptual judgments of TTC, some of which are normally involved in producing reach-to-grasp responses. These activations could not be attributed to actual movement of participants. We demonstrate that networks involved in the computational problem of extracting TTC from expansion information have close correspondence with the sensorimotor systems that would be involved in preparing a timed motor response, such as catching a ball, or avoiding collision.

Temporal interval production and short-term memory

Field, D.T. & Groeger, J.A. (2004)                 pdf preprint
Perception and Psychophysics

Interference with time estimation from concurrent nontemporal processing has been shown to depend on the short-term memory requirements of the concurrent task (Fortin and Breton, 1995; Fortin, Rousseau, Bourque & Kirouac, 1993). In particular, it has been claimed that active processing of information in short-term memory produces interference, whereas simply maintaining information does not. Here, four experiments are reported in which subjects are trained to produce a 2500 msec interval, and then perform concurrent memory tasks. Interference with timing is demonstrated for concurrent memory tasks involving only maintenance. In one experiment, increasing set size in a pitch memory task systematically lengthens temporal production. Two further experiments suggest that this is due to a specific interaction between the short-term memory requirements of the pitch task and those of temporal production. In the final experiment, subjects performed temporal production while concurrently remembering the durations of a set of tones. Interference with interval production was comparable to that produced by the pitch memory task. Results are discussed in terms of a pacemaker-counter model of temporal processing, in which the counter component is supported by short-term memory.