Conditioning influences audio-visual integration by increasing sound saliency

We investigated the effect of prior conditioning an auditory stimulus on audiovisual integration in a series of four psychophysical experiments. The experiments factorially manipulated the conditioning procedure (picture vs. monetary conditioning) and multisensory paradigm (2AFC visual detection vs. redundant target paradigm). In the conditioning sessions, subjects were presented with three pure tones (= conditioned stimulus, CS) that were paired with neutral, positive or negative unconditioned stimuli (US, monetary: +50 euro cents, -50 cents, 0 cents; pictures: highly pleasant, unpleasant and neutral IAPS). In a 2AFC visual selective attention paradigm, detection of near-threshold Gabors was improved by concurrent sounds that had previously been paired with a positive (monetary) or negative (picture) outcome relative to neutral sounds. In the redundant target paradigm, sounds previously paired with positive (monetary) or negative (picture) outcomes increased response speed to both auditory and audiovisual targets similarly. Importantly, prior conditioning did not increase the multisensory response facilitation (i.e. (A+V)/2-AV) or the race model violation. Collectively, our results suggest that prior conditioning primarily increases the saliency of the auditory stimulus per se rather than influencing audiovisual integration directly. In turn, conditioned sounds are rendered more potent for increasing response accuracy or speed in detection of visual targets