Pattern detection in the presence of maskers that differ in spatial phase and temporal offset: threshold measurements and a model

Abstract

Four experiments are described in which brief Gabor patterns are detected in the presence of full-field gratings or Gabor patterns that are superimposed in space, but vary in spatial phase and temporal offset (SOA). E1: Threshold versus masker contrast (TvC) functions were determined for relative phases of 0, 90, 180 and 270° at SOA=0. For 0° relative phase, TvC functions decrease (facilitation) and then increase (masking) as contrast increases. For 90°, there is little or no facilitation and thresholds increase with masker contrast. For 180°, the form of the TvC function varies with observer and conditions. E2: Like E1, except that maskers are Gabor patterns. TvC functions are similar in form to those for full-field maskers, but there is less masking. E3: Forward masking. TvC functions were determined for relative phases of 0, 90, and 180° at SOA=−33 ms. The forms of the TvC functions for 0 and 180° are reversed relative to those at SOA=0. E4: TvP (threshold versus phase) functions were determined for SOA’s of −100, −67, −33, 0 and 33 ms at a constant masker contrast of 0.063. Masking occurs at all relative phases. For simultaneous and backward masking, the threshold is minimum for a relative phase of 0 and maximum at 180°. For forward masking, the form of the function is inverted. A model of pattern masking and facilitation (Foley, J. M. (1994a) Journal of the Optical Society of America A, 11, 1710–1719) is extended to account for masker phase and SOA effects. The model assumes four mechanisms tuned to phases 90° apart, and divisively inhibited by stimuli of all phases. Performance depends on the detection strategy of the observer.