Many past studies have shown that information in one sensory modality affects perception in another modality. Moreover, the relative influence of one modality on another often reflects the reliability of sensory information. For instance, the auditory system has better temporal resolution than vision. When observers are asked to count the number of light flashes in an audio-visual presentation, the number of sound events dominates perception; however, there is little effect of visual temporal structure on auditory judgments. Here, we investigated whether across-modality interactions on perception stimulus intensity are asymmetric when judging changes in light vs. sound intensity.
Seventeen subjects were presented with paired audio-visual stimuli in a two-interval, forced-choice paradigm. In the auditory intensity discrimination session, observers judged which interval containing the louder sound while trying to ignore the light. In the visual intensity discrimination session, they judged which interval containing the brighter light while trying to ignore the sound. In both sessions, the stimulus in the irrelevant modality could be equal in the two intervals of a trial (neutral), could change in the same way as the attended modality (so that the interval that was louder was also brighter; congruent), or could change in the opposite direction (so that the interval that was louder was dimmer; incongruent).
Results showed that the ability to discriminate changes in intensity of the target modality was affected by the changes in the irrelevant modality, both when listeners judged sound and light intensity. In both cases, listeners were best at identifying the direction of the intensity change in the attended modality in congruent trials, intermediate in neutral trials, and worst in the incongruent trials. These observations show that changes in light intensity influence judgments of changes in sound intensity, and vice versa.