The authors used a predictable, externally cued task-switching paradigm to investigate executive control in a severe closed-head injury (CHI) population. Eighteen individuals with severe CHI and 18 controls switched between classifying whether a digit was odd or even and whether a letter was a consonant or vowel on every 4th trial. The target stimuli appeared in a circle divided into 8 equivalent parts. Presentation of the stimuli rotated clockwise. Participants performed the switching task at both a short (200 ms) and a long (1,000 ms) preparatory interval. Although the participants with CHI exhibited slower response times and greater switch costs, similar to controls, additional preparatory time reduced the switch costs, and the switch costs were limited to the 1st trial in the run. These findings indicate that participants with severe CHI were able to take advantage of time to prepare for the task switch, and the executive control processes involved in the switch costs were completed before the 1st trial of the run ended.
Keywordsclosed-head injury; traumatic brain injury; executive functions; task switching; set shifting Multiple-task performance is theorized to involve executive control processes, which supervise the selection, initiation, execution, and termination of each task (e.g., Baddeley, 1986;Logan, 1985;Norman & Shallice, 1986;Rubinstein, Meyer, & Evans, 2001). In the closed-head injury (CHI) literature, much of the research that has addressed multiple-task performance has focused on simultaneous multitask performance rather than successive or rapid alternation multiple-task performance. These studies generally indicate that persons who suffer severe CHI (i.e., brain injury resulting from a rapid acceleration of the head followed by a rapid deceleration without an object penetrating the brain) experience greater difficulty than controls in coordinating and monitoring simultaneous task performances (e.g., Brouwer, Verzendaal, van der