Lateral Interactions in Peripheral Vision

Purpose: When viewed foveally, contrast detection of a Gabor patch (target) is facilitated by collinear, displaced high-contrast Gabor masks (flankers). Polat and Sagi (1994) reported that the same phenomenon occurred in the periphery, but no data was presented. Williams and Hess (1998) found no facilitation in a limited number of conditions tested using a spatial 2AFC paradigm. In the present study, we measured contrast detection in peripheral vision to resolve this conflict in the literature. Methods: Five normally-sighted subjects participated in temporal and spatial forced choice 2AFC experiments. Experiment 1 examined the effect of eccentric viewpoint (2°, 4°, 6° & 12°) on facilitation using 4 test-flanker distances (2, 4 6 & 8λ, where λ=1/cpd) and a spatial frequency of 2cpd. Experiment 2 examined the effect of spatial frequency (1, 2, 4, 6 & 8cpd). Experiment 3 measured the effect of flanker contrast (10, 20, 40 & 80%). Experiment 4 tested the effect of global orientation of the stimulus pattern (vertical or horizontal). In experiments 2, 3 and 4, eccentricity was 4ånd test-flanker distance was 4λ. Results: Facilitation was found to occur in many but not all conditions. Maximum facilitation occurred at a test-flanker distance of 4-6λ, whereas maximum facilitation occurs at 2-3λ in central vision. Facilitation varied between subjects and with spatial frequency. Flanker contrast had no effect over the range evaluated. Equal facilitation was found for both global arrangements of the stimulus pattern. Conclusion: Facilitation of contrast detection does occur in the near periphery of normally-sighted subjects, although the magnitude of the effect is less than found in central vision. The value of such facilitation for persons with central vision impairment needs to be examined.