Abstract
The optokinetic response (OKR) of the eye is induced to follow a large field visual motion. The gain of the OKR (eye velocity / visual motion velocity) is about 0.6 at 1/8Hz in naive goldfish. If the same periodic visual stimulus is given continuously, the OKR gain increases up to 1.0. In addition to the gain increase, goldfish were found to acquire a ‘predictive’ OKR behavior that was named period tuning (PT). Thus OKR velocity decreased before the change in OKS direction as if predicting the OKS timing (Marsh & Baker, 1997). Even if the animal is exposed to complete darkness after the acquisition of PT, its eye velocity follows the similar trajectory to that during training for a while without any visual stimulation. This eye movement in the dark may share a common mechanism with optokinetic after nystagmus (OKAN), and considered to reflect characteristics of the velocity storage mechanism (VSM). To investigate the possible relationship between PT and VSM, we carried out a series of behavioral experiments in goldfish, carp, medaka, zebrafish, and human. We demonstrate that ability to acquire PT is highly dependent on OKAN. This result suggests that VSM is a key mechanism for PT.
