DETECTION FACILITATION BY COLLINEAR STIMULI IN HUMANS - DEPENDENCE ONSTRENGTH AND SIGN OF CONTRAST

We measured detection of a thin vertical line (target) in the presence of a slightly thicker collinear, adjacent line (inducer), Sign and st rength of contrast of the inducer were varied, Test lines could be eit her bright or dark, Detection thresholds were obtained through a tempo ral two-alternative forced-choice (2AFC) procedure with the method of constant stimuli, When target and inducer had equal contrast polarity, low thresholds of target lines were observed for low inducer contrast s and increased with increasing inducer contrast, With opposite contra st polarity of target and inducer, thresholds were high for low induce r contrasts and decreased for increasing contrast thereof, Our results support the hypothesis that cortical mechanisms with different sensit ivity to the sign and strength of contrast participate in the detectio n facilitation of line contours. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.