EVENT-RELATED POTENTIALS AND SELECTIVE ATTENTION

The studies reported here encompassed several different aspects of selective attention and its relationship to endogenous components found with the human auditory event-related potential (ERP).;The first experiment addressed the question of whether or not P3b's automatically occur to all unexpected, low probability stimuli during a task that required the subject's active discrimination. The results were that P3b was always greater in amplitude to designated targets even in the presence of equally unexpected low probability non-targets stimuli.;The second experiment addressed the question of whether or not focusing attention upon one ear is associated with an asymmetric scalp distribution of the endogenous E.R.P. components associated with attention. The amplitudes of ERP components N1, N2 Delta and P3b were measured across the scalp. These findings suggest that the relationship of the endogenous components to selective attention is not accomplished by the simple enhancement or decrement of the activity of the cortical sensory system.;The third experiment addressed the question of whether the amplitudes of endogenous components N2/P3a, N2, and P3b would diminish over time like the amplitude of the exogenous auditory vertex potential (N1/P2) does. The investigation encompassed endogenous components generated by two levels of deviation from a background stimulus in order to see whether or not the magnitude of stimulus shift affected the endogenous components differently over time. The amplitude of the N1/P2 exogenous potential was lower for the second halves of the stimulus blocks. The endogenous components did not diminish in amplitude in the second halves and, in fact, N2/P3a actually increased significantly in amplitude during the second halves of the read-small shift condition. Other endogenous components also behaved differently to differences in stimulus shift; for example, N2 was unaffected by the degree of stimulus shift while P3b was significantly larger for the greater shift. The results demonstrated that endogenous components can differ from each other and from exogenous components in their behavior over time and to stimulus parameters.