Facilitative integration of local motion signals in the peripheral visual field observed in monkey ocular following responses.

To explore how local motion signals in the peripheral visual field are integrated, we recorded ocular following responses (OFRs) to moving vertical gratings extending across a wide horizontal width (1) of various vertical heights, (2) of a thin strip (4° height) at various vertical eccentricities, and (3) of two thin strips separated with various vertical distances (double-grating) in four monkeys. We found that the OFRs became larger and responsive more to lower spatial frequency than to higher as the vertical height of the motion stimuli increased up to 8° or 16°. This result is consistent with the incorporation of visual motion signals originating in the peripheral visual field; the OFRs to thin strips of drifting gratings were tuned for lower spatial frequency as the eccentricity increased. We also found that the OFRs to the double-gratings were quite similar to the sum of the responses to the single gratings in the initial period, but were significantly larger than the linear-sum in the final period. This result suggests that a non-linear mechanism, by which weak local motion signals are integrated into an effective ensemble, underlies the OFRs.