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Effects of age on electrophysiological correlates of speech processing in a dynamic "cocktail-party" situation - PubMed

  • ️Thu Jan 01 2015

Effects of age on electrophysiological correlates of speech processing in a dynamic "cocktail-party" situation

Stephan Getzmann et al. Front Neurosci. 2015.

Abstract

Successful speech perception in multi-speaker environments depends on auditory scene analysis, comprising auditory object segregation and grouping, and on focusing attention toward the speaker of interest. Changes in speaker settings (e.g., in speaker position) require object re-selection and attention re-focusing. Here, we tested the processing of changes in a realistic multi-speaker scenario in younger and older adults, employing a speech-perception task, and event-related potential (ERP) measures. Sequences of short words (combinations of company names and values) were simultaneously presented via four loudspeakers at different locations, and the participants responded to the value of a target company. Voice and position of the speaker of the target information were kept constant for a variable number of trials and then changed. Relative to the pre-change level, changes caused higher error rates, and more so in older than younger adults. The ERP analysis revealed stronger fronto-central N2 and N400 components in younger adults, suggesting a more effective inhibition of concurrent speech stimuli and enhanced language processing. The difference ERPs (post-change minus pre-change) indicated a change-related N400 and late positive complex (LPC) over parietal areas in both groups. Only the older adults showed an additional frontal LPC, suggesting increased allocation of attentional resources after changes in speaker settings. In sum, changes in speaker settings are critical events for speech perception in multi-speaker environments. Especially older persons show deficits that could be based on less flexible inhibitory control and increased distraction.

Keywords: aging; attention; cocktail party; event-related potentials; speech perception.

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Figures

Figure 1
Figure 1

Schematic illustration of the simulated stock-price monitoring scenario. (A) Four loudspeakers were mounted at different locations to the left and right of the subject's median plane. Stimuli were displayed simultaneously via all loudspeakers. (B) Stimuli were spoken by two female (f1, f2) and two male (m1, m2) speakers and consisted of sequences of short company names and numbers. The participants responded to the value of a given target company (here “Bosch,” in bold print), while all other company names had to be ignored. The location of the target company (Location Change), the speaker voice (Voice Change), or both (LocVoice Change) changed following a pseudo-random scheme. Analyses were focused on sequences preceding (Pre) and following a change trial (Post1, Post2, Post3). (C) Superimposed acoustic waveforms of the four streams of words (here: company names “Bosch,” “Deutz,” “EON,” and “Audi,” and numbers “eins,” “vier,” “sechs,” and “sieben”) presented at different locations.

Figure 2
Figure 2

Behavioral results. (A) Rates of correct responses of younger and older adults for Pre, Post1, Post2, and Post3 sequences, and for changes in target speaker location, voice, and combined changes in location and voice (LocVoice). (B) Rates of correct responses (left panel) and changes in the rate of correct responses (same data normalized with reference to pre-change levels; right panel) of younger and older adults, averaged across all types of changes, shown for Pre, Post1, Post2, and Post3 sequences. Error bars are standard errors across participants (N = 22; ***p < 0.001).

Figure 3
Figure 3

Grand-average ERPs. (A) ERPs at Fz, Cz, and Pz plotted as a function of time relative to the speech onset and (B) topographies of the ERP components to the onset of the company name (P1, N1, P2, N2, and N400) and value (P1n and N1n) for Pre, Post1, Post2, and Post3 sequences, and for younger and older participants.

Figure 4
Figure 4

Amplitudes of (A) P1, (B) N1, (C) P2, (D) N2, (E) N400, (F) P1n, and (G) N1n (averaged across the displayed electrode arrays) for Pre, Post1, Post2, and Post3 sequences, shown for younger and older participants. Error bars are standard errors across participants (N = 22). Significance bars and asterisks indicate significant differences between sequences in the younger group (solid), in the older group (dotted), or averaged across both groups (bold; *p < 0.05; **p < 0.01).

Figure 5
Figure 5

Change-related ERPs. (A) Difference waveforms (Post minus Pre) at AFz, Cz, and Pz plotted as a function of time relative to the speech onset and (B) topographies of the change-related ERPs (N400diff, frontal and parietal LPCdiff) for Post1, Post2, and Post3 sequences, shown for younger and older participants.

Figure 6
Figure 6

Amplitudes of the change-related ERPs [(A) N400diff, (B) parietal and (C) frontal LPCdiff; averaged across the displayed electrode arrays] for Post1, Post2, and Post3 sequences, shown for younger and older participants. Error bars are standard errors across participants (N = 22). Significance bars and asterisks indicate significant differences between sequences in the younger group (solid), in the older group (dotted), or averaged across both groups (bold; *p < 0.05; **p < 0.01; ***p < 0.001).

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