Background Huntington's disease (HD) is associated with difficulty performing concurrent tasks, an ability which is a requirement of everyday activities and of potential functional significance in HD.
Aims We compared dual task performance in HD and healthy controls using choice reaction time (CRT) with digit span tasks. We manipulated task difficulty and tested for interactions between difficulty level and group which would indicate differential effects of difficulty on dual tasking in HD.
Methods/techniques 14 participants in the early stages of HD and 14 controls performed two series of dual tasks. Series one paired simple CRT with digit span forward; series two paired complex CRT with digit span backward. Each of the tasks within each series had easy and hard conditions. In the simple CRT easy condition participants viewed single letters and had to press a key labelled Yes if the letter was X or Z or No for other letters. For the hard condition, there were four target letters (X, Z, O, Y); participants had to repeat four (easy) or five (hard) digits forward. The complex CRT task comprised 3×3 matrices of Xs and Os. Participants had to respond whether three Xs (easy) or three Xs or three Os (hard) appeared in a row. Complex CRT was paired with three (easy) or four (hard) digit span backward. Task order was counterbalanced for series, but within series it was proceeded from easier to harder pairs. Measures were speed and accuracy.
Results/outcome Participants with HD were slower and less accurate, a finding that, surprisingly, was more profound in the simple CRT with digit span forward than in the more difficult conditions. Error rates were higher in HD when the simple CRT tasks were performed with the hard digit span forward, suggesting that task difficulty may affect cognitive load in HD.
Conclusion Simple CRT with digit span forward appeared to be more affected in HD than complex CRT with digit span backwards, suggesting that impaired automaticity may underlie attentional deficits in HD.
- Dual task
- choice reaction time
- digit span