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 attentional 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. (JINS, 2012, 18, 1–12)

Huntington's disease (HD) is a neurodegenerative disorder diagnosed clinically with the development of choreiform movements. However, neuropsychological studies have demonstrated cognitive and psychiatric changes during the preclinical phase (pre-HD) prior to formal diagnosis. Previous studies have demonstrated the sensitivity of time reproduction tasks to basal ganglia pathology, as seen in clinical HD and Parkinson's disease. In this study, 29 pre-HD participants, ranging from 3 to 39 years from estimated onset (YEO) of HD based on genetic testing and chronological age, were administered the paced finger-tapping task using target intervals of 600 and 1200 ms. Mean inter-response interval, a measure of timing accuracy, did not systematically deviate from the target interval as a function of YEO. In contrast, timing variability increased curvilinearly as a function of YEO, but not with chronological age alone. Motor timing variability, but not accuracy, may serve as a marker to define the earliest behavioral changes in HD. The present study is among the first to examine the relationship between behavioral measures and YEO in pre-HD. (JINS, 2007, 13, 539–543.)

Recent research has demonstrated some beneficial effects in patients with neglect using rightward shifting prismatic lenses. Despite a great deal of research exploring this effect, we know very little about the cognitive mechanisms underlying prism adaptation in neglect. We examined the possibility that prism adaptation influences visual attention by having healthy participants complete either a reflexive or a voluntary covert visual attention cuing paradigm before and after adaptation to leftward, rightward, or sham (no shift) prisms. The results for reflexive orienting demonstrated that a subset of participants with large cuing effects before prism adaptation were faster to reorient attention away from an invalid cue on the side of space opposite the prismatic shift post adaptation. For voluntary orienting, left prisms increased the efficiency of voluntary attention in both left and right visual space in participants with a small cuing effect before prism adaptation. In contrast, right prisms decreased the efficiency of voluntary attention in both left and right space for participants with a large cuing effect before prism adaptation. No significant effects were observed in the sham prism groups. These results suggest that prism adaptation may exert a variety of influences on attentional orienting mechanisms. (JINS, 2006, 12, 337–349.)