Effect of Hemispheric Asymmetry on Performance in Auditory Vigilance Task

The study was aimed to determine whether both performance level and performance decrement differ across hemispheres in difficult signal detection task. Sixty-five subjects had to detect the threshold auditory signal presented to the left/right ears randomly. Both hits and false alarm rate were significantly higher, whereas reaction time was shorter in the right hemisphere (RH) than in left one (LH). The clear-cut effect of hemispheres on the slope of response time to hits was obtained: the temporal performance decrement for the RH was higher than for the LH. Results correspond to previous findings (see Parasuraman et al, 1998, for review) and suggest the predominant involvement of the RH into the processes of signal detection and sustained attention. Extraversion seems to be the personality variable mediating the way in which hemispheric performance strategies should be applied to the task. Introverts compared with extraverts seem to use the LH processing strategies more often than extraverts. A large body of lesion data supports that the right hemisphere (RH) is an important part of the circuitry, which implements both alertness and vigilance. Localization of damage in the right frontal lobes reduces signal detection performance [Wilkins et al. 1987]. One of possible mechanisms underlying this effect may be the impairment of processes sustaining the alertness state. Yokogama et al. (1987) found that the normal deceleration of heart rate response that occurs during the preparatory interval of a warned RT task was absent in RH-damaged patients not in LH-damaged ones. Posner & Petersen (1990) proposed that one of the three attentional subsystems – the vigilance system was right lateralized. Auditory discrimination task is linked to increasing of glucose metabolism in the right middle prefrontal cortex [Cohen et al. 1992]. The involvement of the RH seems to be important not only for initial analysis of a signal but also for further processing of a stimulus in short-term memory. After binaural simultaneous presentation of two standard stimuli the subjects were presented a test signal with 1 sec delay and they had to respond whether there was a test signal among two standards or not. In this study the left ear/right hemisphere advantage was obtained [Bruder et al. 1991]. The RH superiority in visual vigilance tasks was found [Whitehead, 1991, Dimond, Beamont, 1973, 1979]. However this effect is less consistent than in auditory modality.