Gratings: why frequency discrimination is sometimes better than detection.

Two models that assume independent processing among frequency-selective analyzers are presented. These are a distance model and an integration model derived from signal-detection theory. The models permit quantitative comparisons between detection and discrimination performance and lead to an empirical comparison that is sensitive to effects of correlated noise and interactions among the responding mechanisms. The stimuli were four pairs of sine-wave gratings that differed in spatial-frequency separation. They were presented to observers in a signal-detection rating paradigm, which was used for both detection and discrimination judgments. The results indicate the presence of properties, such as inhibitory interactions or correlated noise among responding mechanisms, that favor discrimination over detection.