Two-frame apparent motion presented with an inter-stimulus interval reverses optokinetic responses in mice.

Two successive image frames presented with a blank inter-stimulus interval (ISI) induce reversals of perceived motion in humans. This illusory effect is a manifestation of the temporal properties of image filters embedded in the visual processing pathway. In the present study, ISI experiments were performed to identify the temporal characteristics of vision underlying optokinetic responses (OKRs) in mice. These responses are thought to be mediated by subcortical visual processing. OKRs of C57BL/6 J mice, induced by a 1/4-wavelength shift of a square-wave grating presented with and without an ISI were recorded. When a 1/4-wavelength shift was presented without, or with shorter ISIs (≤106.7 ms), OKRs were induced in the direction of the shift, with progressively decreasing amplitude as the ISI increased. However, when ISIs were 213.3 ms or longer, OKR direction reversed. Similar dependence on ISIs was also obtained using a sinusoidal grating. We subsequently quantitatively estimated temporal filters based on the ISI effects. We found that filters with biphasic impulse response functions could reproduce the ISI and temporal frequency dependence of the mouse OKR. Comparison with human psychophysics and behaviors suggests that mouse vision has more sluggish response dynamics to light signals than that of humans.