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1.  Differential Callosal Contributions to Bimanual Control in Young and Older Adults 
Journal of cognitive neuroscience  2010;23(9):10.1162/jocn.2010.21600.
Our recent work has shown that older adults are disproportionately impaired at bimanual tasks when the two hands are moving out of phase with each other [Bangert, A. S., Reuter-Lorenz, P. A., Walsh, C. M., Schachter, A. B., & Seidler, R. D. Bimanual coordination and aging: Neurobehavioral implications. Neuropsychologia, 48, 1165–1170, 2010]. Interhemispheric interactions play a key role during such bimanual movements to prevent interference from the opposite hemisphere. Declines in corpus callosum (CC) size and microstructure with advancing age have been well documented, but their contributions to age deficits in bimanual function have not been identified. In the current study, we used structural magnetic resonance and diffusion tensor imaging to investigate age-related changes in the relationships between callosal macrostructure, microstructure, and motor performance on tapping tasks requiring differing degrees of interhemispheric interaction. We found that older adults demonstrated disproportionately poorer performance on out-of-phase bimanual control, replicating our previous results. In addition, older adults had smaller anterior CC size and poorer white matter integrity in the callosal midbody than their younger counterparts. Surprisingly, larger CC size and better integrity of callosal microstructure in regions connecting sensorimotor cortices were associated with poorer motor performance on tasks requiring high levels of interhemispheric interaction in young adults. Conversely, in older adults, better performance on these tasks was associated with larger size and better CC microstructure integrity within the same callosal regions. These findings implicate age-related declines in callosal size and integrity as a key contributor to bimanual control deficits. Further, the differential age-related involvement of transcallosal pathways reported here raises new questions about the role of the CC in bimanual control.
doi:10.1162/jocn.2010.21600
PMCID: PMC3809031  PMID: 20954936
2.  Reaching for Words and Non-Words: Interactive effects of word frequency and stimulus quality on the characteristics of reaching movements 
Psychonomic bulletin & review  2012;19(3):513-520.
Word frequency and stimulus degradation produce large and additive effects in the onset latencies of lexical decision responses. The influence of these two variables was examined in a lexical decision task where continuous arm reaching responses were required and movement trajectories were tracked. The results yielded the typical additive pattern of word frequency and stimulus degradation on reaction time and movement duration. Importantly, however, an examination of movement trajectories revealed interactive effects of word frequency and stimulus degradation that emerged for the early part of the movement. These findings suggest that factors thought to influence early stages of stimulus identification continue to influence the dynamics of the response after response initiation, motivating a need to reevaluate current models of lexical decision performance. Moreover, this work highlights how the dynamics of naturalistic multi-dimensional responses provide a richer source of information about decision-making processes than discrete uni-dimensional measures.
doi:10.3758/s13423-012-0234-x
PMCID: PMC3685575  PMID: 22419404
3.  Keep up the pace: Declines in simple repetitive timing differentiate healthy aging from the earliest stages of Alzheimer’s disease 
The current study examined whether healthy older adults (OA) and individuals at the earliest stages of dementia of the Alzheimer’s type (DAT) differ from younger adults (YA) and from each other on a simple, extended continuous tapping task using intervals (500 ms, 1000 ms, and 1500 ms) thought to differentially engage attention control systems. OA groups sped up their tapping at the slowest target rate compared to the YA; this pattern was magnified in the early stage DAT groups. Performance variability appeared especially sensitive to DAT-related changes, as reliable differences between healthy OA and very mild DAT individuals emerged for multiple tap rates. These differences are proposed to result from breakdowns in attentional control that disrupt error-correction processes and the ability to resolve discrepancies between internally-generated temporal expectancies and the external temporal demands of the repetitive timing task.
doi:10.1017/S1355617712000860
PMCID: PMC3505757  PMID: 22929329
Aging; Attention; Alzheimer type dementia; Dementia; Time perception; Sensory motor performance
4.  Dissecting the Clock: Understanding the mechanisms of timing across tasks and temporal intervals 
Acta psychologica  2010;136(1):20-34.
Currently, it is unclear what model of timing best describes temporal processing across millisecond and second timescales in tasks with different response requirements. In the present set of experiments, we assessed whether the popular dedicated scalar model of timing accounts for performance across a restricted timescale surrounding the 1 second duration for different tasks. The first two experiments evaluate whether temporal variability scales proportionally with the timed duration within temporal reproduction. The third experiment compares timing across millisecond and second timescales using temporal reproduction and discrimination tasks designed with parallel structures. The data exhibit violations of the assumptions of a single scalar timekeeper across millisecond and second timescales within temporal reproduction; these violations are less apparent for temporal discrimination. The finding of differences across tasks suggests that task demands influence the mechanisms that are engaged for keeping time.
doi:10.1016/j.actpsy.2010.09.006
PMCID: PMC3019300  PMID: 20955998
Time; Time perception; Time estimation; Prospective timing; Scalar timing PsycINFO classification: 2340
5.  Bimanual Coordination and Aging: Neurobehavioral Implications 
Neuropsychologia  2009;48(4):1165-1170.
We investigate whether aging leads to global declines in discrete and continuous bimanual coordination tasks thought to rely on different control mechanisms for temporal coupling of the limbs. All conditions of continuous bimanual circle drawing were associated with age-equivalent temporal control. This was also true for discrete simultaneous tapping. Older adults’ between-hand coordination deficits were specific to discrete tapping conditions requiring asynchronous intermanual timing and were associated with self-reported executive dysfunction on the Dysexecutive (DEX) questionnaire. Also, older adults exclusively showed a relationship between the most difficult bimanual circling condition and a measure of working memory. Thus, age-related changes in bimanual coordination are specific to task conditions that place complex timing demands on left and right hand movements and are, therefore, likely to require executive control.
doi:10.1016/j.neuropsychologia.2009.11.013
PMCID: PMC2828502  PMID: 19941878
Executive Control; Motor Control; Bimanual Coordination; Aging

Results 1-5 (5)