Visually guided locomotion in the gerbil: a comparison of open- and closed-loop control.

Two experiments were conducted in order to explore the effects of visual feedback on control of locomotion in the gerbil. In the first experiment, gerbils were trained to run down an alleyway towards a visual target in order to obtain food reward. One group of animals was trained to run to a target whose size never varied while another group was trained to run to a target whose size varied randomly from trial to trial. On some trials, the target's size was changed dynamically during running to determine whether gerbils used this dynamic size change information to compute time to collision (tau). Results suggested that neither group used retinal image size information but both groups seemed able to compute tau. In a second experiment, gerbils were trained in the same way as in experiment 1, but on some trials the target was extinguished during the run. In this condition, probe trials showed that gerbils used retinal image size to compute target distance. Collectively, the results showed that gerbils were able to rapidly and flexibly utilize available information to complete a visually guided running task. The results are discussed in the context of the psychophysics of cue combination and its neural underpinnings.