Abstract
In electroencephalography (EEG) measurements, processing of periodic sounds in the ascending auditory pathway generates the frequency-following response (FFR) phase-locked to the fundamental frequency (F0) and its harmonics of a sound. We measured FFRs to the steady-state (vowel) part of syllables /ba/ and /aw/ occurring in binaural rapid streams of speech sounds as frequently repeating standard syllables or as infrequent (p = 0.2) deviant syllables among standard /wa/ syllables. Our aim was to study whether concurrent active phonological processing affects early processing of irrelevant speech sounds reflected by FFRs to these sounds. To this end, during syllable delivery, our healthy adult participants performed tasks involving written letters delivered on a computer screen in a rapid stream. The stream consisted of vowel letters written in red, infrequently occurring consonant letters written in the same color, and infrequently occurring vowel letters written in blue. In the phonological task, the participants were instructed to press a response key to the consonant letters differing phonologically but not in color from the frequently occurring red vowels, whereas in the non-phonological task, they were instructed to respond to the vowel letters written in blue differing only in color from the frequently occurring red vowels. We observed that the phonological task enhanced responses to deviant /ba/ syllables but not responses to deviant /aw/ syllables. This suggests that active phonological task performance may enhance processing of such small changes in irrelevant speech sounds as the 30-ms difference in the initial formant-transition time between the otherwise identical syllables /ba/ and /wa/ used in the present study.
Highlights
Baddeley’s influential working-memory model (e.g., Baddeley and Hitch, 1974; Baddeley, 1992) proposes that the so-called articulatory-phonological loop underlies auditory working memory and is involved in processing of written visual inputs
The significant Task × Deviance interaction resulted from enhanced deviant vs. standard frequency-following response (FFR) difference during Phonological Task in relation to Non-Phonological Task, but it is not possible to judge from the present data whether attenuation of FFR to standard /ba/ during Phonological Task in relation to Non-Phonological Task contributed to this deviant vs. standard FFR difference
The aim of the present study was to clarify whether processing of infrequent syllable changes in the ascending auditory pathway reflected by FFRs would be affected by a concurrent visual phonological task
Summary
Baddeley’s influential working-memory model (e.g., Baddeley and Hitch, 1974; Baddeley, 1992) proposes that the so-called articulatory-phonological loop underlies auditory working memory and is involved in processing of written visual inputs. This model was supported by our recent functional magnetic resonance imaging (fMRI) results (Salo et al, 2013). Auditory cortex (AC) activity in response to spoken syllables is attenuated during phonological processing of written consonant letters in relation to AC activity elicited by the spoken syllables during non-phonological tasks involving the letters, that is, discriminating their font color or location rather than their phonological content. Such attention-related modulation of AC activity is a common finding in fMRI studies on attention to speech or non-speech sounds (for a review and meta-analysis, see Alho et al, 2014), as well as in related studies applying electro- or magnetoencephalography (EEG and MEG, respectively; for reviews, see Näätänen et al, 2002; Fritz et al, 2007; Alain et al, 2013)
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