Abstract
Foveal cone detection is often modeled as if subjects pool signal information over the extent of the stimulus. We sought to determine if subjects use this optimal detection strategy by measuring detection thresholds for stimuli presented either in blocks of known size or with the same sizes randomly intermixed. Detection thresholds and color appearance were not significantly different in the blocked and interleaved conditions, indicating that subjects employed the same detection strategy in both cases. This precludes the optimal strategy in which pooling is flexible based on a priori stimulus information. In a linear response framework, performance was also inconsistent with both independent cone detection and summation over a single, fixed pooling area. Results were consistent with a model of detection incorporating independent signal combination across multiple channels pooling over various spatial extents. Detection thresholds and color appearance were simultaneously measured in 4 subjects using multiple response criteria. Dim, brief (30 ms), monochromatic (550 nm) spot stimuli of 4 sizes (1.7′, 4.1′, 9.9′ and 25′) were presented to the dark-adapted fovea through a 2 mm artificial pupil. Thresholds and color reports were compared between blocked and intermixed conditions, and detection thresholds were compared to model predictions. Detection thresholds and color appearance were not significantly different in the blocked and interleaved conditions, indicating that subjects employed the same detection strategy in both cases. This precludes the optimal strategy in which pooling is flexible based on a priori stimulus information. In a linear response framework, performance was also inconsistent with both independent cone detection and summation over a single, fixed pooling area. Results were consistent with a model of detection incorporating independent signal combination across multiple channels pooling over various spatial extents.