Speech perception as an active cognitive process

Abstract

One view of speech perception is that acoustic signals are transformed into representations for pattern matching to determine linguistic structure. This process can be taken as a statistical pattern-matching problem, assuming realtively stable linguistic categories are characterized by neural representations related to auditory properties of speech that can be compared to speech input. This kind of pattern matching can be termed a passive process which implies rigidity of processing with few demands on cognitive processing. An alternative view is that speech recognition, even in early stages, is an active process in which speech analysis is attentionally guided. Note that this does not mean consciously guided but that information-contingent changes in early auditory encoding can occur as a function of context and experience. Active processing assumes that attention, plasticity, and listening goals are important in considering how listeners cope with adverse circumstances that impair hearing by masking noise in the environment or hearing loss. Although theories of speech perception have begun to incorporate some active processing, they seldom treat early speech encoding as plastic and attentionally guided. Recent research has suggested that speech perception is the product of both feedforward and feedback interactions between a number of brain regions that include descending projections perhaps as far downstream as the cochlea. It is important to understand how the ambiguity of the speech signal and constraints of context dynamically determine cognitive resources recruited during perception including focused attention, learning, and working memory. Theories of speech perception need to go beyond the current corticocentric approach in order to account for the intrinsic dynamics of the auditory encoding of speech. In doing so, this may provide new insights into ways in which hearing disorders and loss may be treated either through augementation or therapy.

Perceptual restoration of masked speech in human cortex

“…In particular, it will be important to disentangle the independent and interacting contributions of stochastic brain states133536 that reflect ongoing task-irrelevant activity but impact perception, and predictive signals152937, which may be related to learned lexical representations3839. Our results do not unambiguously disentangle these two possibilities, however there is evidence that both may deeply influence perception.…”

“…Even under clear listening conditions, the internal dynamics of speech perception networks are highly influenced by predictions related to multiple levels and timescales of linguistic and memory representations172829. Our results suggest a role for left inferior frontal cortex in generating these predictions and bias signals during speech perception.…”

Understanding environmental sounds in sentence context

“…Regardless, the need for attention reallocation did not impair participants’ ability to make use of context information to speed processing. This suggests that signal source changes (e.g., timbre, voice, speech/nonspeech) can slow recognition but still engage the same processes that are also needed for sentence understanding (Heald & Nusbaum, 2014a). …”

How may the basal ganglia contribute to auditory categorization and speech perception?

“…Significantly, however, differences in task characteristics may have important consequences for the manner by which learning is achieved (Box 1) inasmuch as they engage distinct basal ganglia-thalamo-cortical loops. Overt, category learning tasks that provide feedback about the accuracy of a speech category judgment may promote learning by directing explicit attention to sounds to discover critical stimulus characteristics relevant to category membership (Logan et al, 1991; Francis and Nusbaum, 2002; Heald and Nusbaum, 2014). Learning of explicit goal-directed actions based on feedback appears to be mediated by the anterior portion of the dorsal striatum, which interacts with executive and attention/working memory systems.…”