Predictive processing increases intelligibility of acoustically distorted speech: Behavioral and neural correlates

Description: We studied neural mechanisms by which previous experiences and acoustic information are integrated allowing successful comprehension of severely acoustically distorted speech. In our functional magnetic resonance imaging (fMRI) study, acoustically distorted sentences were disambiguated by an exposure to their acoustically intact counterparts. In a separate behavioral experiment, intelligibility was significantly enhanced from 41% to 95% by such disambiguation. Contrasting the blood oxygenation level dependent (BOLD) -responses elicited by the acoustically distorted sentences as intelligible vs. unintelligible (i.e., before vs. after the presentation of their intact counterparts) revealed increased activity in the brain areas associated with retrieval mode, that is, a process where incoming sensory input is treated as retrieval cue that is compared to the representations stored in memory. Decreased BOLD-responses, in turn, were observed in the left-hemispheric fusiform gyrus, the right-hemispheric parahippocampal gyrus and supramarginal gyrus as well as bilaterally, in the brain area covering the middle insular cortex and extending to the middle superior temporal sulcus. BOLD-suppression may reflect priming where neurons coding features essential in sentence recognition attenuate the responses of other neurons resulting sentence-specific neural representation. Our results suggest that retrieval mode and priming may facilitate processing of distorted speech increasing the likelihood of the successful match between auditory input and the corresponding memory representation. This conclusion would be in line with the currently advocated predictive nature of memory, suggesting that one of the main functions of memory could be biasing the perception of ambiguous sensory information towards the interpretation that has the highest probability to be correct on the basis of previous experience.

Related article: http://doi.org/10.1002/brb3.789