Enhancement of perceived visual intensity by auditory stimuli: a psychophysical analysis.

Abstract Judgments of the intensity of a stimulus are dependent on the level of central nervous system activity it generates. Generally, it is assumed that such judgments are based on activity along modality-specific pathways. Thus, visual intensity judgments would be based on unimodal visual activity. However, many neurons do not fit neatly within modality-specific categories, but can be influenced by more than one sensory modality. Often the "multisensory" effect is quite pronounced. If these multisensory neurons participate in such fundamental functions as perceived intensity, the presence of a nonvisual (i.e., auditory) cue may have a significant effect on the perceived intensity of a visual cue. The results of the present study were consistent with such a hypothesis. A brief, broad-band auditory stimulus was found to significantly enhance the perceived intensity of an LED. The effect was most pronounced at the lowest visual intensities, and was evident regardless of the location of the auditory cue. However, it was present only at the location of visual fixation. Yet, despite the significant influence of the auditory cue, and its differential effect at different visual intensities, a power function that maintains the proportionality among perceived visual intensities was retained.