Mitchell G. Longstaff

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Response time (RT) is a commonly used measure of cognitive performance, which is usually characterized as stochastic. However, useful information may be hidden in the apparently random fluctuations of RT. Dynamical systems analysis techniques allow an exploration of the alternative hypothesis that RT fluctuations are deterministic, albeit in a complex(More)
OBJECTIVES To systematically investigate the ability of Parkinson's disease patients to discretely and dynamically scale the size of continuous movements and to assess the impact of movement size on outcome variability. METHODS Ten patients with Parkinson's disease (mean age 72 years) were compared with 12 healthy elderly controls (mean age 70 years). The(More)
This study investigated spiral drawing performance as an indicator of fine motor function, as well as to gain insight into adaptive movement strategies used by people with multiple sclerosis (MS). Seven people with MS, nine younger controls (mean age of 20) and eight older controls (mean age of 40) drew spirals on a graphics tablet at a comfortable speed(More)
Two experiments tested how changing a planned movement affects movement initiation and execution in idiopathic Parkinson's disease (PD) patients. In Experiment 1, PD patients, elderly controls, and young adults performed discrete aiming movements to one of two targets on a digitizer. A precue (80% valid cue and 20% invalid cue of all trials) reflecting the(More)
Modern graphical and computational techniques for detecting nonlinearity in psychological data sets are presented. These procedures allow researchers to determine the information complexity of temporal data, using physiological and psychological measurements, and to provide evidence for chaos in time series contaminated by measurement noise. Problems with(More)
This study examined the impact of target geometry on the trajectories of rapid pointing movements. Participants performed a graphic point-to-point task using a pen on a digitizer tablet with targets and real time trajectories displayed on a computer screen. Circular- and elliptical-shaped targets were used in order to systematically vary the accuracy(More)
The complex dynamics of the human hand/arm system need to be precisely controlled to produce fine movements such as those found in handwriting. This study employs dynamical systems analysis techniques to further understand how this system is controlled when it is functioning well and when it is compromised through motor function degradation (e.g. from(More)
The time-based resource-sharing (TBRS) model of working memory indicates that secondary tasks that capture attention for relatively long periods can result in the interference of working memory processing and maintenance. The current study investigates if discrete and continuous movements have differing effects on a concurrent, verbal serial recall task. In(More)
Previous research has assumed that writing is a cognitively complex task, but has not determined if writing overloads Working Memory more than reading and listening. To investigate this, participants completed three recall tasks. These were reading lists of words before recalling them, hearing lists of words before recalling them, and hearing lists of words(More)
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