The influence of dichotical fusion on the redundant signals effect, localization performance, and the mismatch negativity

In two experiments, each including a simple reaction time (RT) task, a localization task, and a passive oddball paradigm, the physical similarity between two dichotically presented auditory stimuli was manipulated. In both experiments, a redundant signals effect (RSE), high localization performance, and a reliable mismatch negativity (MMN) was observed for largely differing stimuli, suggesting that these are coded separately in auditory memory. In contrast, no RSE and a localization rate close to chance level (experiment 1) or at chance (experiment 2) were observed for stimuli differing to a lesser degree. Crucially, for such stimuli a small (experiment 1) or no (experiment 2) MMN were observed. These MMN results indicate that such stimuli tend to fuse into a single percept and that this fusion occurs rather early within information processing.