Causal inference regulates audiovisual spatial recalibration via its influence on audiovisual perception

To obtain a coherent perception of the world, our senses need to be in alignment. When we encounter misaligned cues from two sensory modalities, the brain must infer which cue is faulty and recalibrate the corresponding sense. We examined whether and how the brain uses cue reliability to identify the miscalibrated sense by measuring the audiovisual ventriloquism aftereffect for stimuli of varying reliability. Visual spatial reliability was smaller, comparable to and greater than that of auditory stimuli. To adjust for modality-specific biases, visual stimulus locations were chosen based on perceived alignment with auditory stimulus locations for each participant. During audiovisual recalibration, participants were presented with bimodal stimuli with a fixed perceptual spatial discrepancy; they localized one modality, cued after stimulus presentation. Unimodal auditory and visual localization was measured before and after the recalibration phase. We compared participants’ behavior to the predictions of three models of recalibration: (a) Reliability-based: each modality is recalibrated based on its relative reliability—less reliable cues are recalibrated more; (b) Fixed-ratio: the degree of recalibration for each modality is fixed; (c) Causal-inference: recalibration is directly determined by the discrepancy between a cue and its final estimate, which in turn depends on the reliability of both cues, and inference about how likely the two cues derive from a common source. Vision was hardly recalibrated by audition. Auditory recalibration by vision changed idiosyncratically as visual reliability decreased: the extent of auditory recalibration either decreased monotonically, first increased and then decreased, or increased monotonically. The latter two patterns cannot be explained by either the reliability-based or fixed-ratio models. Only the causal-inference model of recalibration captures the idiosyncratic influences of cue reliability on recalibration. We conclude that cue reliability, causal inference, and modality-specific biases guide cross-modal recalibration indirectly by determining the perception of audiovisual stimuli. Author summary Audiovisual recalibration of spatial perception occurs when we receive audiovisual stimuli with a systematic spatial discrepancy. The brain must determine to which extent both modalities should be recalibrated. In this study, we scrutinized the mechanisms the brain employs to do so. To this aim, we conducted a classical recalibration task in which participants were adapted to spatially discrepant audiovisual stimuli. The visual component of the bimodal stimulus was either less, equally, or more reliable than the auditory component. We measured the amount of recalibration by computing the difference between participants’ unimodal localization responses before and after the recalibration task. Across participants, the influence of visual reliability on auditory recalibration varied fundamentally. We compared three models of recalibration. Only a causal-inference model of recalibration captured the diverse influences of cue reliability on recalibration found in our study, and this model is able to replicate contradictory results found in previous studies. In this model, recalibration depends on the discrepancy between a cue and its final estimate. Cue reliability, perceptual biases, and the degree to which participants infer that the two cues come from a common source govern audiovisual perception and therefore audiovisual recalibration.