Neural correlates of switching from auditory to speech perception

Abstract

Many people exposed to sinewave analogues of speech first report hearing them as electronic glissando and, later, when they switch into a dspeech modeT, hearing them as syllables. This perceptual switch modifies their discrimination abilities, enhancing perception of differences that cross phonemic boundaries while diminishing perception of differences within phonemic categories. Using high-density evoked potentials and fMRI in a discrimination paradigm, we studied the changes in brain activity that are related to this change in perception. With ERPs, we observed that phonemic coding is faster than acoustic coding: The electrophysiological mismatch response (MMR) occurred earlier for a phonemic change than for an equivalent acoustic change. The MMR topography was also more asymmetric for a phonemic change than for an acoustic change. In fMRI, activations were also significantly asymmetric, favoring the left hemisphere in both perception modes. Furthermore, switching to the speech mode significantly enhanced activation in the posterior parts of the left superior gyrus and sulcus relative to the non-speech mode. When responses to a change of stimulus were studied, a cluster of voxels in the supramarginal gyrus was activated significantly more by a phonemic change than by an acoustic change. These results demonstrate that phoneme perception in adults relies on a specific and highly efficient left-hemispheric network, which can be activated in top-down fashion when processing ambiguous speech/non-speech stimuli.

Individual differences in the acquisition of second language phonology

“…Thus, the above dissociations that we find in performance with the two stimulus types may be due not only to the fact that one is speech and the other not, but they may also be due to stimulus complexity. In support of the idea that different learning mechanisms exist for speech and non-speech sounds, there exists evidence from other studies for speech-specific neural mechanisms when stimulus complexity is controlled (Liebenthal, Binder, Spitzer, Possing, & Medler, 2005;Scott, Blank, Rosen, & Wise, 2000;Scott, Rosen, Lang, & Wise, 2006), or when the same stimuli are first perceived as nonspeech and then later as speech (Dehaene-Lambertz et al, 2005;Dufor, Serniclaes, Sprenger-Charolles, & Démonet, 2007). More generally, it is likely that the neural mechanisms underlying the processing of abstract, linguistically relevant properties versus of the underlying acoustic characteristics of stimuli interact in a complex and non-exclusive manner, and that they depend on linguistic experience as well as on neural top-down processing mechanisms which interact with afferent pathways which carry stimulus information (Zatorre & Gandour, 2007).…”

Motor Representations of Articulators Contribute to Categorical Perception of Speech Sounds

“…The left posterior superior temporal cortex shows greater responses to speech than to nonspeech sounds (Binder et al, 2000). Furthermore, sine-wave analogues of sounds elicit stronger activity in this region when they are perceived as speech (i.e., phonetically and categorically) than when they are perceived as nonspeech (i.e., nonphonetically and continuously) (Dehaene-Lambertz et al, 2005;Möttönen et al, 2006;Desai et al, 2008). The supramarginal gyrus is also thought be involved in categorical processing of speech sounds (Raizada and Poldrack, 2007).…”

Attentional and linguistic interactions in speech perception

“…Several recent studies comparing phonetic sounds to acoustically matched nonphonetic sounds (Dehaene-Lambertz et al, 2005;Liebenthal et al, 2005;Mottonen et al, 2006) or to noise (Binder et al, 2000;Rimol et al, 2005) have shown activation specifically in this brain region. Two factors might explain these discordant findings.…”