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.