Perceptual and decisional contributions to audiovisual interactions in the perception of apparent motion: a signal detection study

Motion information available to different sensory modalities can interact at both perceptual and post-perceptual (i.e., decisional) stages of processing. However, to date, researchers have only been able to demonstrate the influence of one of these components at any given time, hence the relationship between them remains uncertain. We addressed the interplay between the perceptual and post-perceptual components of information processing by assessing their influence on performance within the same experimental paradigm. We used signal detection theory to discriminate changes in perceptual sensitivity (d') from shifts in response criterion (c) in performance on a detection (Experiment 1) and a classification (Experiment 2) task regarding the direction of auditory apparent motion streams presented in noise. In the critical conditions, a visual motion distractor moving either leftward or rightward was presented together with the auditory motion. The results demonstrated a significant decrease in sensitivity to the direction of the auditory targets in the crossmodal conditions as compared to the unimodal baseline conditions that was independent of the relative direction of the visual distractor. In addition, we also observed significant shifts in response criterion, which were dependent on the relative direction of the distractor apparent motion. These results support the view that the perceptual and decisional components involved in audiovisual interactions in motion processing can coexist but are largely independent of one another.