Early lexical influences on sublexical processing in speech perception: Evidence from electrophysiology

Abstract

Contextual information influences how we perceive speech, but it remains unclear at which level of processing contextual information merges with acoustic information. Theories differ on whether early, sublexical speech processing levels are strictly feed-forward or are influenced by semantic and lexical context. Studies using behavioral responses have shown contextual factors influence sublexical judgments but are unable to pinpoint whether context biases responses by modulating sublexical processing or later response selection stages. In the current study, we investigate the time-course of context effects by simultaneously recording electroencephalography as an online measure of sublexical speech processing while subjects engage in a lexically biasing phoneme categorization task. We find that lexical context modulates the amplitude of the N100, an ERP component linked with sublexical processes in speech perception. These results support interactive accounts of speech perception over accounts in which early speech perception processes are only driven by bottom up information.

Lexical influences on categorical speech perception are driven by a temporoparietal circuit

“…Adaptation studies-in which continuum sounds are presented repetitively and/or in serial order (Eimas and Corbit, 1973;Miller, 1975 causing a boundary shift in the direction toward the un-adapted detector at the polar end of the continuum (Rozsypal et al, 1985). As confirmed empirically, larger boundary shifts would be expected for less strongly categorized continua (Rozsypal et al, 1985), e.g., vowels vs. stop consonants (Altmann et al, 2014), acoustically degraded speech (Bidelman et al, 2020;, and for ambiguous speech tokens as shown here and previously (Ganong, 1980;Gow et al, 2008;Lam et al, 2017;Myers and Blumstein, 2008;Noe and Fischer-Baum, 2020).…”

“…Our data are best cast in terms of interactive rather than serial frameworks of speech perception as in the TRACE model of spoken word recognition (McClelland and Elman, 1986). As confirmed empirically (Ganong, 1980;Gow et al, 2008;Lam et al, 2017;Myers and Blumstein, 2008;Noe and Fischer-Baum, 2020), these models predict stronger lexical biasing when speech sounds carry ambiguity. Indeed, neural correlates of the Ganong effect were most evident at the midpoint of our speech continua, where word influences exert their strongest effect.…”

“…In attempts to resolve these conflicting models, Gow et al (2008) used functional connectivity analyses applied to MEG data and showed that causal neural signaling directed from left SMG to "lower-level" areas (e.g., STG) modulates sensory representations for speech within a latency of 280-480 ms (Gow et al, 2008). The top-down nature of their effects strongly favored a feedback, perceptual account of the Ganong whereby lexical representations influence the earlier encoding of sublexical speech features (e.g., Myers and Blumstein, 2008;Noe and Fischer-Baum, 2020;van Linden et al, 2007).…”

“…Rather than acting at late stages, lexical biasing could instead manifest via top-down (and perhaps bi-directional) modulations of early perceptual processing with the lexical interface. Indeed, growing evidence from neuroimaging studies (Gow et al, 2008;Myers and Blumstein, 2008;Noe and Fischer-Baum, 2020;van Linden et al, 2007) reaffirms such interactive, connectionist views of categorization (e.g., TRACE;McClelland and Elman, 1986). Employing fMRI with a Ganong task, Myers and Blumstein (2008) found that the placement of the phonetic boundary modulated activity both in perceptual [e.g., superior temporal gyrus, STG), inferior parietal lobule (IPL)] and frontal executive brain areas (IFG, ACC), with greater activity for ambiguous items near the boundary.…”

“…Employing fMRI with a Ganong task, Myers and Blumstein (2008) found that the placement of the phonetic boundary modulated activity both in perceptual [e.g., superior temporal gyrus, STG), inferior parietal lobule (IPL)] and frontal executive brain areas (IFG, ACC), with greater activity for ambiguous items near the boundary. The mere involvement of the STG strongly suggested lexical shifts not due solely to executive decision processes but at minimum, includes a perceptual component that either itself has direct access to lexical properties or is interactively reactivated to integrate phonetic and extra-phonetic factors in placing the phonetic boundary (Gow et al, 2008;Myers and Blumstein, 2008;Noe and Fischer-Baum, 2020). While fMRI offers excellent spatial characterization of potential lexical effects, it lacks the temporal precision necessary to resolve the underlying brain dynamics of category formation (Bidelman et al, 2013) and related lexical influences (Gow et al, 2008), both of which unfold within a few hundred milliseconds after speech onset (e.g., Mahmud et al, 2020).…”