Binocular interaction with neutral density filters as measured by the visual evoked response.

The influence of neutral density (ND) filters on the pattern visually evoked response (VER) was investigated as a function of check size. Monocular and binocular transient pattern reversal VER's were recorded through three ND filters (0.6, 1.0, and 2.6 log units) before 1 eye on 55 adult subjects using 5.5 min arc and 50 min arc check sizes. The 5.5 min arc check produced responses which suggest that partial binocular summation is present in the absence of ND filters but disappears as the filter density increases. In the case of the 50 min arc check size the presence of binocular summation is less certain and a 1.0 log unit ND filter produces binocular inhibition which may be due to latency differences between the two eyes. Eye dominancy appears to have no effect on these results.