We used the electromagnetic search coil technique to record the short-latency tracking eye movements (Ocular Following Responses, OFR) elicited in 3 human subjects by horizontal motion applied to vertical grating patterns composed of 2 sinusoids of spatial frequency 3f and 5f, which created a repeating pattern with beat frequency, f. Motion consisted of successive steps (100 Hz), each 1/4 of the wavelength of the beat, so that with each step the 2 components shifted 1/4 of their wavelengths and hence had different apparent speeds and opposite directions, the 5f forwards and the 3f backwards. The contrasts of the 2 components were varied independently over the range 0-64%. When the contrast of one component was less than about half that of the other, the component with the higher contrast dominated initial OFR and the component with the lower contrast had almost no influence: winner-take-all (WTA). When their contrasts were more similar, both components exerted an influence on initial OFR: vector sum/averaging. This pattern of behavior was evident over a wide range of contrasts. We repeated these experiments using grating patterns composed of 2 sinusoids of frequency 3f and 7f, which again created a repeating pattern with beat frequency, f. The steps were again each 1/4 of the beat wavelength so that with each step the 2 components shifted 1/4 of their wavelengths and hence again had different apparent speeds but this time the same (backward) direction. Initial OFR was now always in the backward direction and, when the contrast of one component was less than about 1/3 that of the other, the component with the higher contrast determined the speed of initial OFR and the component with the lower contrast had almost no influence: winner-take-all (WTA). When their contrasts were more similar, again both components exerted an influence on initial OFR: vector sum/averaging. Thus, if the 2 components differed sufficiently in contrast, initial OFR showed WTA behavior whether those components moved in the same or opposite direction.
Showing the most recent 10 out of 22 publications
