Abstract
The present study investigated the effects of sequence complexity, defined in terms of phonemic similarity and phonotoactic probability, on the timing and accuracy of serial ordering for speech production in healthy speakers and speakers with either hypokinetic or ataxic dysarthria. Sequences were comprised of strings of consonant-vowel (CV) syllables with each syllable containing the same vowel, /a/, paired with a different consonant. High complexity sequences contained phonemically similar consonants, and sounds and syllables that had low phonotactic probabilities; low complexity sequences contained phonemically dissimilar consonants and high probability sounds and syllables. Sequence complexity effects were evaluated by analyzing speech error rates and within-syllable vowel and pause durations. This analysis revealed that speech error rates were significantly higher and speech duration measures were significantly longer during production of high complexity sequences than during production of low complexity sequences. Although speakers with dysarthria produced longer overall speech durations than healthy speakers, the effects of sequence complexity on error rates and speech durations were comparable across all groups. These findings indicate that the duration and accuracy of processes for selecting items in a speech sequence is influenced by their phonemic similarity and/or phonotactic probability. Moreover, this robust complexity effect is present even in speakers with damage to subcortical circuits involved in serial control for speech.
Highlights
Since Lashley’s seminal paper [1] outlining the “problem of serial order” in speech production and other movement behaviors, the process underlying fluent ordering of speech sounds and syllables has been an area of active research interest
The present study investigated the processes responsible for selecting speech items during speech production and whether the timing and accuracy of these selection processes are affected by sequence complexity
These effects were observed for healthy speakers as well as speakers with hypokinetic and ataxic dysarthria
Summary
Since Lashley’s seminal paper [1] outlining the “problem of serial order” in speech production and other movement behaviors, the process underlying fluent ordering of speech sounds and syllables has been an area of active research interest. Sequence complexity effects on speech error rates and segment and syllable durations were evaluated in speakers with hypokinetic dysarthria secondary to Parkinson’s disease and speakers with ataxic dysarthria to determine whether these speaker groups exhibited deficits in serial performance related to either similarity-based or usage-based aspects of serial processing for speech production. There are few studies that address how these factors influence the selection of speech items over the course of sequence production and almost no studies addressing these processes in speakers with dysarthria To examine this issue, the current study evaluated measures of sound and syllable durations during production of sequences that varied in complexity based on their phonemic similarity and phonotactic probability. The present analyses of sound and syllable durations were designed to supplement the reaction time finding of Spencer and Rogers [53] and provide an integrated account of complexity effects both prior to and during sequence production
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