Simultaneous visual detection and identification: theory and data.

A signal-detection model is presented for the two-alternative forced-choice procedure that gathers simultaneous detection and identification judgments. By using vector representation, a measure of independent processing within the visual system is derived. The independence measure is applied to data on the detection and identification of stimuli that differ along the dimensions of orientation, spatial frequency, and size. Data are presented that favor the signal-detection model over a high-threshold model.