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The psychophysical lateral interaction paradigm of Polat and Sagi  was adapted to make it suitable for VEP recording. We focused only on the long range interactions between non-overlapping test-mask combinations. The amplitude and phase of the steady-state VEP elicited by small Gabor patches were measured as a function of stimulus contrast with and without laterally placed patches of similar or different orientations. VEP recording requires a temporal modulation signal to time-lock the signal analysis that is necessary to extract the VEP from the EEG background noise, and thus the Gabors were contrast modulated at 4.1 Hz. The foveal Gabors were either presented alone or in the presence of two flanking Gabors of fixed contrast (50%). The flanks, also modulated at 4.1 Hz, were placed above and below the foveal Gabor and were oriented either vertically (collinear) or horizontally (non-collinear). The flank response was also measured separately. The existence of non-linear lateral interactions was inferred from failures in a linearity of test and flank response-summation.
Interaction effects similar to these seen psychophysically were observed in the evoked potential experiments . VEP responses were larger and faster for collinear targets and masks than was predicted by the linear sum of separate target and mask responses. Responses were smaller and slower for orthogonal orientations of target and mask. The range of the interaction for the collinear configuration observed in the VEP was up to or 9-12 wavelengths --- similar to Polat & Sagi's limit of 12 wavelengths. Facilitation was maximum at and decreased as a function of distance and was non-significance than the isolated target response level at .