Pavlovian conditioning of perceptual neural responses. An fMRI study.

Background A modified sensory preconditioning paradigm, called sensory conditioning (SC), provides a framework for studying incidental learning and predictive processing through probabilistic associations between neutral sensory stimuli in the absence of reinforcement. SC is a form of statistical learning in which repeated exposure to sensory regularities leads to implicit learning. Although previous work has shown SC-related changes in cross-modal cortical activity, the representational content of these effects has remained unclear. Aims We here tested whether associative learning between task-irrelevant but probabilistically related auditory and visual stimuli induces conditioned neural responses to predictive auditory cues encoding specific sensory information about the expected visual stimuli. Methods Twenty participants underwent fMRI recordings during an implicit SC paradigm, involving probabilistic manipulation of audiovisual stimuli pairings across five days. Results fMRI data showed that the brain encodes cross-modal transitional and distributional regularities independently of stimulus salience and explicit behavior. This encoding produced stimulus-specific modulation of cortical responses to predictive and expected stimuli, with early generation of neural priorities at the onset of predictive cues. Learned associations persisted across days and generalized beyond specific stimulus pairs, including stimulus omission. Discussion Our results provide the first empirical evidence that SC results in specific crossmodal effects consisting of auditory CS evoking a visual brain response similar to that of the expected visual CS. Consistent with predictive coding principles and Hebbian learning, our findings indicate that associative processes occur essentially at the neural level, where explicit behavior is merely an ancillary component.