Cognitive Load Affects Speech Motor Performance Differently in Older and Younger Adults

Purpose The aim of this study was to determine the impact of cognitive load imposed by a speech production task on the speech motor performance of healthy older and younger adults. Response inhibition, selective attention, and working memory were the primary cognitive processes of interest. Method Twelve healthy older and 12 healthy younger adults produced multiple repetitions of 4 sentences containing an embedded Stroop task in 2 cognitive load conditions: congruent and incongruent. The incongruent condition, which required participants to suppress orthographic information to say the font colors in which color words were written, represented an increase in cognitive load relative to the congruent condition in which word text and font color matched. Kinematic measures of articulatory coordination variability and movement duration as well as a behavioral measure of sentence production accuracy were compared between groups and conditions and across 3 sentence segments (pre-, during-, and post-Stroop). Results Increased cognitive load in the incongruent condition was associated with increased articulatory coordination variability and movement duration, compared to the congruent Stroop condition, for both age groups. Overall, the effect of increased cognitive load was greater for older adults than younger adults and was greatest in the portion of the sentence in which cognitive load was manipulated (during-Stroop), followed by the pre-Stroop segment. Sentence production accuracy was reduced for older adults in the incongruent condition. Conclusions Increased cognitive load involving response inhibition, selective attention, and working memory processes within a speech production task disrupted both the stability and timing with which speech was produced by both age groups. Older adults' speech motor performance may have been more affected due to age-related changes in cognitive and motoric functions that result in altered motor cognition.