Abstract
AIM: To investigate the detection and discrimination of Glass patterns on pulsed and steady luminance pedestals that provide different background adaptation. METHOD: Stimuli were presented for 26.7 ms on a 9.6 × 9.6 deg achromatic pedestal on a uniform 14 × 10 deg background of 12 cd/m2. In the Pulsed-Pedestal (PP) condition, the pedestal appeared only during the stimulus interval. The observer maintained adaptation to the uniform background. In the Steady-Pedestal (SP) condition, the pedestal appeared during the entire period, thus the observer adapted to the background-plus-pedestal. The Glass and random patterns both contained 130, 0.38 deg diameter dots. The method was temporal 2AFC. In the detection experiment, a dot pattern, either a circular Glass pattern or random dots, plus the pedestal appeared in one interval, and the pedestal alone in the other. The observer chose the interval with a dot pattern. In the discrimination experiment, a Glass pattern appeared in one interval and a random pattern in the other. The observer chose the interval with a Glass pattern. In both experiments, the independent variable was dot contrast, with thresholds estimated by a staircase procedure. RESULTS: There were no systematic differences in the detection thresholds for Glass and random patterns. Observers were able to perceive the global form of Glass patterns in both SP and PP conditions including PP conditions where parvocellular mediation was favored (Pokorny & Smith JOSA A, 1997). The discrimination thresholds required about 0.1 log unit greater contrast than the detection thresholds for both the PP and SP conditions. CONCLUSIONS: The inclusion of global form information in the dot pattern did not influence the absolute detection thresholds. The contrast increment from the detection thresholds required for the discrimination task was small, and almost constant for all the pedestal conditions.