Effects of Sleep Loss on Information-Processing in an Absolute Judgment Task as a Function of Task Difficulty

The effects of 36 hours of sleep loss on information-processing were assessed in an absolute judgment task. Of the 24 subjects employed, 12 served in the sleep-loss (experimental) and control conditions, respectively. All subjects were tested individually for a total of ten sessions; the control group was tested on ten consecutive days, whereas the experimental subjects were tested every four hours over a 36-hour period of sleep loss, and at a recovery session following approximately 12 hours of rest and recovery. The task required subjects to make absolute judgments of the size of two small circles of light and to identify each stimulus presented as the larger or smaller of the two. In each session, subjects worked with four different pairs of circles, at four levels of discrimination difficulty (difficulty level was defined in terms of the similarity of the sizes of the circles in each pair). Performance was assessed in terms of reaction times, errors, and rates of information transmission. The study was designed to determine if sleep loss reduces the efficiency of information-processing, if these effects are reflected in speed or accuracy of response, and finally, if task difficulty (as defined by stimulus discriminability, or similarity) influences the magnitude of these effects. The results indicated that sleep loss had adverse effects on information-processing, as reflected in increased reaction times and decreased information transmission rates in the experimental group; performance in the control group improved across test sessions on both measures. Response accuracy did not change significantly across sessions in either group. A significant interaction between task difficulty and sleep loss was obtained, but only with the reaction time measure. The magnitude of the increase in reaction times increased monotonically with task difficulty; the same trend was noted in the rate of information transmission measure, but was not of sufficient magnitude to attain statistical significance. The results are consistent with the hypothesis that sleep loss results in a general degradation in the efficiency of information-processing, to an extent determined by task difficulty or cognitive processing "load".