Sensory function in multimodal signal detection.

Five observers detected a sinusoid in noise in a two‐interval forced‐choice experiment. The signal could occur on an earphone, on an oscilloscope, or on both devices simultaneously. Detection performance was studied as related to (1) mode of occurrence of the signal(s); (2) the external noise correlation in the auditory and visual channels; and (3) the observers' a priori knowledge of the mode of occurrence of the signal. The observed improvement in sensitivity (measured in d′ units) as a function of bimodal signal presentation closely followed the predictions of a statistical summation model and was much lower than predicted by linear and probabilistic addition models. Under conditions of independence of noise in the auditory and visual channels, some improvements in sensitivity were of almost 3 dB. The improvement in sensitivity afforded by a priori knowledge of the mode of occurrence of the signal was less for bimodal signals than for unimodal signals.