Event-related potential evidence that very slowly presented auditory stimuli are passively processed differently in younger and older adults.

The occurrence of a very infrequent and unattended auditory stimulus is highly salient and may result in an interruption of the frontoparietal network controlling processing priorities. Research has suggested that older adults may be unable to compute the level of salience of unattended stimulus inputs. A multi-channel EEG was recorded in 20 younger adults and 20 older adults. In different conditions, a single 80 dB SPL auditory stimulus was presented relatively rapidly, every 1.5 s or very slowly, every 12.0 s. Participants ignored the auditory stimuli while watching a silent video. When the stimuli were presented rapidly, group differences were not observed for the amplitudes of N1 and P2, which peaked at 100 and 180 ms respectively. When stimuli were presented very slowly, their amplitudes were much enhanced for younger adults, but did not increase for older adults. The failure to observe a large increase in the amplitude of N1 and P2 in older adults for very slowly presented auditory stimuli provides strong evidence of a dysfunction of the salience network in this group.