Monetary 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 three psychophysical experiments. The three experiments employed the same acquisition phase (monetary conditioning) but different multisensory paradigms (Exp1: 2AFC visual detection; Exp2: redundant target paradigm; Exp3: redundant target paradigm using near threshold visual and auditory stimuli). In the acquisition phase, subjects were presented with three pure tones (= conditioned stimuli, CSs) that were paired with positive, negative or neutral unconditioned stimuli (USs, monetary: +50 euro cents, -50 cents, 0 cents). 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 outcome relative to neutral sounds. Taken together, redundant target paradigms results showed that sounds previously paired with positive or negative 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