Does experience in talking facilitate speech repetition?

Abstract

Speech is unique among highly skilled human behaviors in its ease of acquisition by virtually all individuals who have normal hearing and cognitive ability. Vocal imitation is essential for acquiring speech, and it is an important element of social communication. The extent to which age-related changes in cognitive and motor function affect the ability to imitate speech is poorly understood. We analyzed the distributions of response times (RT) for repeating real words and pseudowords during fMRI. The average RT for older and younger participants was not different. In contrast, detailed analysis of RT distributions revealed age-dependent differences that were associated with changes in the time course of the BOLD response and specific patterns of regional activation. RT-dependent activity was observed in the bilateral posterior cingulate, supplementary motor area, and corpus callosum. This approach provides unique insight into the mechanisms associated with changes in speech production with aging.

Fig. 1

Distributions of RTs grouped by age and type of word. (a, b, c, d). The histograms were calculated with a bin width of 40 ms. The solid curve is the best fit of an ex-Gauss function, and the dotted curve is the best fit of a Gaussian function. (e) Mean RTs calculated by age and type of word. (f, g, h). Best-fit estimates of the parameters μ, σ, and τ for the ex-Gauss function fitted to the RT distributions shown in panels a–d. Each error bar is an estimate of the standard error of the parameter value, calculated from the Hessian matrix in QMPE/CML. Significant differences (Likelihood Ratio test, p < .0001) are marked by a bracket and asterisk.

Fig. 2

Brain activation associated with word type by age by time interaction. (a) Activation in posterior cingulate. The color bar codes for the F values. (b) Estimated time courses of the RT-correlated signal for the repetition of pseudowords (upper panel) and real words (lower panel) for each age group.

Fig. 3

Brain activation associated with age by time interaction. (a) Activation in SMA and corpus callosum. The color bar codes for the F values. (b) Estimated time courses of the RT-correlated signal for each age group for SMA (upper panel) and corpus callosum (lower panel). The responses to real words and pseudowords were combined within each age group for this analysis.