Numerous studies have demonstrated that selective attention to color is associated with a larger neural response under attend than ignore conditions, but have not addressed whether this difference reflects enhanced activity under attend or suppressed activity under ignore. In this study, a color-neutral condition was included, which presented stimuli physically identical to those under attend and ignore conditions, but in which color was not task relevant. Attention to color did not modulate the early sensory-evoked P1 and N1 components. Traditional ERP markers of early selection (the anterior Selection Positivity and posterior Selection Negativity) did not differ between the attend and neutral conditions, arguing against a mechanism of enhanced activity. However, there were markedly reduced responses under the ignore relative to the neutral condition, consistent with the view that early selection mechanisms reflect suppression of neural activity under the ignore condition.

Selective attention reflects the top-down control of sensory processing that is mediated by enhancement or inhibition of neural activity. ERPs were used to investigate age-related differences in neural activity in an experiment examining selective attention to color under Attend and Ignore conditions, as well as under a Neutral condition in which color was task-irrelevant. We sought to determine whether differences in neural activity between old and young adult subjects were due to differences in age rather than executive capacity. Old subjects were matched to two groups of young subjects on the basis of neuropsychological test performance: one using age-appropriate norms and the other using test scores not adjusted for age. We found that old and young subject groups did not differ in the overall modulation of selective attention between Attend and Ignore conditions, as indexed by the size of the anterior Selection Positivity. However, in contrast to either young adult group, old subjects did not exhibit reduced neural activity under the Ignore relative to Neutral condition, but showed enhanced activity under the Attend condition. The onset and peak of the Selection Positivity occurred later for old than young subjects. In summary, older adults execute selective attention less efficiently than matched younger subjects, with slowed processing and failed suppression under Ignore. Increased enhancement under Attend may serve as a compensatory mechanism.

Older adults exhibit a reduced ability to ignore task-irrelevant stimuli; however, it remains to be determined where along the information processing stream the most salient age-associated changes occur. In the current study, event related potentials (ERPs) provided an opportunity to determine whether age-related differences in processing task-irrelevant stimuli were uniform across information processing stages or disproportionately affect either early or late selection. ERPs were measured in young and old adults during a color-selective attention task in which subjects responded to target letters in a specified color (attend condition) while ignoring letters in a different color (ignore condition). Old subjects were matched to two groups of young subjects on the basis of neuropsychological test performance: one using age-appropriate norms and the other using test scores not adjusted for age. There were no age-associated differences in the magnitude of early selection (attend – ignore), as indexed by the size of the anterior selection positivity (SP) and posterior selection negativity (SN). During late selection, as indexed by P3b amplitude, both groups of young subjects generated neural responses to target letters under the attend versus ignore conditions that were highly differentiated. In striking contrast, old subjects generated a P3b to target letters with no reliable differences between conditions. Individuals who were slow to initiate early selection appeared to be less successful at executing late selection. Despite relative preservation of the operations of early selection, processing delays may lead older subjects to allocate excessive resources to task-irrelevant stimuli during late selection.