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The unity assumption is influenced by exogenous and endogenous factors:

  • degree of discrepancy between cross-modal percepts,
  • active involvement (in proprioception),
  • awareness of discrepancy,
  • expectation,
  • compellingness.

The ``unity assumption'' is the hypothesized unconscious assumption (or the belief) of an observer that stimuli in different modalities representing a single cross-sensory object.

Vatakis and Spence found support for the concept of a `unity assumption' in an experiment in which participants were to judge whether a visual lip stream or an auditory utterance was presented first: Participants found this task easier if the visual and auditory stream did not match in terms of gender of voice or content, suggesting that their unity hypothesis was weak in these cases, causing them not to integrate them.

In an audio-visual localization task, Wallace et al. found that their subjects' localization of the auditory stimulus were usually biased towards the visual stimulus whenever the two stimuli were perceived as one and vice-versa.

The unity assumption can be interpreted as a prior (if interpreted as an expectation of a forthcoming uni- or cross-sensory stimulus) or a mediator variable in a Bayesian inference model of multisensory integration.