Simultaneous measurements of detection thresholds and color appearance: does attending to color appearance impact detection?

Abstract

Purpose - Threshold measurements and color appearance reports with small spot stimuli each provide insight into the nature of spatial and color vision. However, they are typically performed separately and the extent to which subjects register hue for very dim stimuli, or to which attending to color interferes with detection are not known. This is problematic for modeling near-threshold hue responses. A simultaneous detection and hue judgment task is used to investigate the interaction between threshold measurement and color reporting. Methods - Rating scales (3 subjects) were used to simultaneously measure color appearance and detection thresholds in the dark adapted fovea at multiple response criteria. A dim, brief (6 msec), monochromatic (580 nm) small spot stimulus (FWHM ∼1′) was viewed with conventional optics (2 mm pupil). In randomized blocks subjects were instructed to rate detection, color appearance, or both. Results - Simultaneous rating of both color appearance and detection confidence did not elevate thresholds above those for either task performed independently. In fact simultaneous judgments appeared to facilitate detection for two subjects. Color responses were not significantly different between the simultaneous and color rating only tasks. Conclusions - The cognitive burden of simultaneous color and detection judgments did not negatively impact either judgment individually. Data for two subjects suggests attention to color appearance during threshold measurements can decrease threshold, as if allowing access to otherwise unavailable stimulus information. Along with its efficiency, this dual judgment task provides a means of measuring the dependence of color appearance on subjective criterion.