Abstract
Bayesian accounts of perception, such as predictive processing, suggest that perceptions integrate expectations and sensory experience, and thus assimilate to expected values. Furthermore, more precise expectations should have stronger influences on perception. We tested these hypotheses using a within-subject paradigm with social cues consisting of what participants were told were ratings from 10 prior participants, but which were actually constructed to independently manipulate the cue mean, variance (precision), and skewness independent of the actual stimulus intensity delivered. Forty-five participants reported their expectations regarding the painfulness of thermal stimuli or the visual contrast of flickering checkerboards. In a second session, similar (sham) cues were each followed by either a noxious thermal or a visual stimulus. Perceptions assimilated to cue-based expectations in both modalities, but precision effects were modality-specific: more precise cues enhanced assimilation in visual perception only, while higher uncertainty slightly increased reported pain. fMRI analysis revealed that the cues affected higher-level affective and cognitive systems--including assimilation to the cue mean in the Stimulus Intensity-Independent Pain Signature-1 (SIIPS-1), a neuromarker of endogenous pain processing--and in the nucleus accumbens. There were no predictive cue effects on the Neurological Pain Signature (NPS), a neuromarker of nociceptive pain. Region of interest analyses showed activity consistent with aversive prediction-error-like encoding in the periaqueductal gray during pain perception, but no cue or prediction error-related responses in early perceptual processing systems. Furthermore, behavioral and computational models of the expectation session revealed that expectations construction was biased towards extreme cue values in both modalities, and towards low-pain cues specifically. These findings suggest that predictive processing theories should be extended with mechanisms such as selective attention to outliers, and that expectation generation and its perceptual effects vary by sensory modality and primarily influence higher-level processes rather than early perception, at least when cues are not reinforced.