The initial ocular following response (OFR) to moving grating patterns: Evidence for winner-take-all mechanisms

Abstract

We recorded the OFR elicited in 3 human subjects by horizontal motion applied to vertical grating patterns consisting of a sum of two sinusoids of spatial frequency 3f and 5f, which created a repeating pattern with a “beat” at frequency, f. Motion consisted of successive steps, each ¼ of the wavelength of the beat, so that the 2 components each shifted ¼ of their wavelength, the 5f forwards and the 3f backwards. The contrast of the 3f component was varied systematically from 1% to 64% while the contrast of the 5f component was fixed at 0% or 8%. The OFR was recorded with the search coil technique. When the 5f component had 0% contrast, initial OFR was in the backward direction and its amplitude increased roughly linearly with the log contrast of the 3f sine wave. When the 5f component had 8% contrast and the contrast of the 3f component ranged from 1% to 4%, initial OFR was in the forward direction and its amplitude remained almost constant; as the contrast of the 3f component increased further, initial OFR reversed direction and, when the contrast of the 3f component exceeded 16%, the amplitude of the initial OFR showed a dependence on log contrast that was almost the same as that in the first experiment when the 5f component was absent. Thus, if the contrast of one component was less than ½ that of the other then the weaker component had almost no influence on the initial OFR: winner-take-all. We repeated these experiments using grating patterns consisting of a sum of two sinusoids of frequency 3f and 7f. The steps were again ¼ of the beat wavelength so that each component again shifted ¼ of its wavelength but this time in the same (backward) direction. Initial OFR was now always in the backward direction and its magnitude was again largely insensitive to the component with the lower contrast. Thus, if the 2 components differed in contrast by >50%, initial OFR showed winner-take-all behavior whether those components moved in the same or opposite direction.

Footnotes

 Supported by the Intrameural Program of the National Eye Institute