Driving performance during word generation--testing the function of human brain lateralization using fTCD in an ecologically relevant context.

It has been hypothesized that cerebral lateralization of function enhances cognitive performance. Evidence was found in birds and fish. However, recent research in humans did not support this hypothesis. We aimed to replicate and extend these findings for single- and dual-task performance in an ecologically relevant task. We combined a word generation task which is assumed to be primarily processed in the left hemisphere with a driving task which is assumed to be primarily processed in the right hemisphere. For each task the individual strength and direction of hemispheric lateralization was assessed by using functional transcranial Doppler sonography (fTCD). For each subject (36 right-handed, 35 nonright-handed) performance was measured in the two single-tasks and in the dual-task condition. On average, subjects showed a left hemisphere bias for the word generation task, a right hemisphere bias for the driving task and dual-task interference. Within subjects, lateralization of language and driving were statistically independent. In accordance with earlier studies, the results show no indication of a positive effect of strength of lateralization on performance in single-tasks or dual-task efficiency. We also found no advantage of a typical compared to an atypical or a contralateral compared to an ipsilateral lateralization pattern. In right-handers, but not in nonright-handers, we even found a negative relationship between strength of lateralization and dual-task efficiency for atypically lateralized subjects. This further supports the suggestion that lateralization does not enhance cognitive performance in humans.

Divided attention in experienced young and older drivers: lane tracking and visual analysis in a dynamic driving simulator.

A simulated driving task that required the simultaneous execution of two continuous visual tasks was administered to 12 healthy young (mean age 26.1 years) and 12 healthy older (mean age 64.4 years) experienced and currently active drivers. The first task was a compensatory lane-tracking task involving a three-dimensional road display. The second task was a timed, self-paced visual analysis task involving either a vocal or manual binary response to dot patterns projected within the road display. Using adaptive tasks, single-task difficulty was individually adjusted for each subject. To control for individual differences in attention allocation strategy, the dual task was performed according to three different sets of instructions based on the relative importance of each task. Compared with young adults, older adults showed a significantly decreased ability to divide attention. This effect was apparent in lane tracking and in the accuracy of visual analysis. The impairment of divided attention was less pronounced in the vocal condition than in the manual one. This suggests that difficulty in integrating responses may be an important determinant of poor dual-task performance in old age.

Divided attention 5 to 10 years after severe closed head injury.

The ability to divide attention of persons who had sustained a severe Closed Head Injury 5 to 10 years before (chronic CHI patients), was examined in a dual-task experiment administered to 15 CHI patients and 34 control subjects. Both the patient group and the control group consisted of active licenced drivers at the time of the investigation. One task was a compensatory tracking task requiring lane tracking, a basic skill or car driving. The other task was a self-paced visual choice reaction time task. Single-task difficulty was individually adjusted by adaptive task procedures (on both tasks CHI patients reached significantly lower performance levels in single task conditions). With individual differences in single-task performance thus controlled, the ability to divide attention was found to be approximately equal in the chronic CHI patients and the control group. A surprising finding in this light, however, was the significant positive correlation between severity of injury (PTA duration) and divided attention costs in the patient group.

Age differences in divided attention in a simulated driving task.

The ability of young, middle-aged, and old adults to divide attention was examined using a dual task experiment involving two continuous performance tasks. The first task was a compensatory tracking task modeled after the important everyday activity of car driving. The second task was a self-paced visual choice-reaction time task requiring analysis of a small visual display presented in such a way that no eye movements were required when the two tasks had to be performed simultaneously. Single-task difficulty was individually adjusted for each subject. Performance-Operating-Characteristics were used to control for individual differences in attention allocation strategies. Even when individual differences in single task performance were adequately controlled for, elderly adults showed a significantly decreased ability to divide attention when compared with young and middle-aged adults. Young and middle-aged adults did not differ in the ability to divide attention.

Sustained attention and sustained effort after closed head injury: detection and 0.10 Hz heart rate variability in a low event rate vigilance task.

In closed head injury patients impaired sustained attention has been used to explain poor performance of complex tasks. However, this basic capacity was never adequately investigated. We investigated sustained attention in an auditory vigilance task and found no evidence at all for an impairment. With an interval of about three months 8 patients, tested in the first half year after closed head injury, and 8 healthy control subjects were confronted twice with a low event rate vigilance task. This yielded measures of signal detection and response latency. Also the amplitude of 0.10 Hz Heart Rate Variability, a power spectral measure, was calculated to indicate sustained effort. Hypotheses that patients would manifest stronger effects of time-on-task on performance and effort were not supported. Independent of sustained attention patients differed from controls in terms of response latencies and sensitivity of discriminating small differences of loudness especially on the first occasion.