J. A. Whitfield, Z. Kriegel, A. M. Fullenkamp, and D. D. Mehta, “Effects of concurrent manual task performance on connected speech acoustics in individuals with Parkinson disease,” Journal of Speech, Language, and Hearing Research, vol. 62, no. 7, pp. 2099–2117, 2019. Publisher's VersionAbstract
    Purpose: Prior investigations suggest that simultaneous
    performance of more than 1 motor-oriented task may
    exacerbate speech motor deficits in individuals with
    Parkinson disease (PD). The purpose of the current
    investigation was to examine the extent to which
    performing a low-demand manual task affected the
    connected speech in individuals with and without PD.
    Method: Individuals with PD and neurologically healthy
    controls performed speech tasks (reading and
    extemporaneous speech tasks) and an oscillatory
    manual task (a counterclockwise circle-drawing
    task) in isolation (single-task condition) and concurrently
    (dual-task condition).
    Results: Relative to speech task performance, no changes
    in speech acoustics were observed for either group when
    the low-demand motor task was performed with the
    concurrent reading tasks. Speakers with PD exhibited
    a significant decrease in pause duration between the
    single-task (speech only) and dual-task conditions
    for the extemporaneous speech task, whereas control
    participants did not exhibit changes in any speech
    production variable between the single- and dual-task
    Conclusions: Overall, there were little to no changes in
    speech production when a low-demand oscillatory motor
    task was performed with concurrent reading. For the
    extemporaneous task, however, individuals with PD
    exhibited significant changes when the speech and manual
    tasks were performed concurrently, a pattern that was
    not observed for control speakers.
    Supplemental Material:
    J. A. Whitfield and D. D. Mehta, “Examination of clear speech in Parkinson disease using passage-level vowel space metrics,” Journal of Speech, Language, and Hearing Research, vol. 62, no. 7, pp. 2082–2098, 2019. Publisher's VersionAbstract
    Purpose: The purpose of the current study was to characterize
    clear speech production for speakers with and without
    Parkinson disease (PD) using several measures of working
    vowel space computed from frequently sampled formant
    Method: The 1st 2 formant frequencies were tracked for
    a reading passage that was produced using habitual and
    clear speaking styles by 15 speakers with PD and 15 healthy
    control speakers. Vowel space metrics were calculated
    from the distribution of frequently sampled formant frequency
    tracks, including vowel space hull area, articulatory–acoustic
    vowel space, and multiple vowel space density (VSD)
    measures based on different percentile contours of the
    formant density distribution.
    Results: Both speaker groups exhibited significant
    increases in the articulatory–acoustic vowel space and
    VSD10, the area of the outermost (10th percentile)
    contour of the formant density distribution, from habitual
    to clear styles. These clarity-related vowel space increases
    were significantly smaller for speakers with PD than
    controls. Both groups also exhibited a significant increase
    in vowel space hull area; however, this metric was not
    sensitive to differences in the clear speech response
    between groups. Relative to healthy controls, speakers
    with PD exhibited a significantly smaller VSD90, the area
    of the most central (90th percentile), densely populated
    region of the formant space.
    Conclusions: Using vowel space metrics calculated from
    formant traces of the reading passage, the current work
    suggests that speakers with PD do indeed reach the more
    peripheral regions of the vowel space during connected
    speech but spend a larger percentage of the time in more
    central regions of formant space than healthy speakers.
    Additionally, working vowel space metrics based on the
    distribution of formant data suggested that speakers with
    PD exhibited less of a clarity-related increase in formant
    space than controls, a trend that was not observed for
    perimeter-based measures of vowel space area.