Statistical learning decreases sensitivity to temporal asynchrony of events within as well as across modalities

Abstract

Co-association of an auditory and a visual event due to frequent co-occurrence have been reported to increase the size of their temporal binding window, that is the range of asynchronicity between the onset of the two events at which observers perceive them occurring simultaneously. According to a probabilistic interpretation, co-occurrence strengthens the prior that the two events originate from a common cause resulting in a higher degree of perceptual integration across modalities despite contradicting sensory evidence. However, statistical learning creating associations is considered to be a domain-general mechanism and as such, it should facilitate similar integration within a single modality as well, where distinctiveness of the two modalities cannot help. Using a simultaneity judgement task, we tested this conjecture by examining the change of observers' sensitivity to asynchrony after implicit learning of co-occurrences within the visual modality. In a learning phase (LP), observers saw arbitrary shape-pairs moving synchronously in a random direction. In the test phase, three types of pairs were presented: 1) visual pairs seen during the LP, 2) pairs from the LP in a new combination, 3) pairs with completely new shapes. The asynchrony between the movement onset of the elements was manipulated. Observers showing learning during LP (N= 24) reported a higher proportion of simultaneity judgments, as quantified by higher temporal binding windows for the learned pairs than for the newly combined or novel visual pairs (p< 0.05) indicating an increased probability of unisensory integration despite identical sensory evidence. Thus, prior experience of high co-occurrence alters the perceived relation of elements in time within a single modality the same way as it does across modalities. These results point to a general mechanism of sensory binding across the entire spectrum of sensory input space.