The Dissociation between Early and Late Selection in Older Adults

Abstract

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.

Age-related decline in differentiated neural responses to rare target versus frequent standard stimuli

“…Otherwise, observed differences between groups could be due not to age, but to other factors (Alperin et al, 2013; Daffner et al, 2011b; Daselaar & Cabeza, 2005; Riis et al, 2008). Because there is strong evidence that selective attention reflects top-down control mechanisms (de Fockert, Rees, Frith, & Lavie, 2001; Gazzaley et al, 2008; Rissman, Gazzaley, & D'Esposito, 2009; Zanto, Rubens, Thangavel, & Gazzaley, 2011), age groups were matched in terms of executive capacity.…”

“…Increased allocation of these resources (as indexed by a larger P3b amplitude to standards) was associated with fewer false alarms. Addressing why older subjects need these extra cognitive resources to be as accurate as younger subjects is beyond the scope of the current paper, but may be related to impairments in early stimulus processing and/or the delivery of degraded information for late selection and stimulus categorization (Alperin et al, 2013). …”

“…The attend condition consisted of all stimuli in the designated color; the ignore condition consisted of all stimuli in the non-designated color. Of note, the current study only examined the P3 activity in response to target and standard stimuli presented under the attend condition (see Alperin et al, 2013 for results comparing the attend vs. ignore condition).…”

“…In previous work, we compared P3b responses to letter stimuli under attend and ignore conditions that were based on a non-spatial feature (color) (Alperin et al, 2013). We found that young adults generated a robust P3b in response to designated target letters in the attended but not ignored color, demonstrating a clearly differentiated neural response between conditions.…”

“…First, many ERP studies that have examined age-related dedifferentiation, including our own, compared responses to the same class of stimuli under attend vs. ignore conditions (Alperin et al, 2013; Hahn et al, 2011; Lorenzo-Lopez et al, 2007), but have not investigated responses to different classes of stimuli under an attend condition only. Second, almost all prior reports have limited their investigation to young adults in their 20s and young-old adults in their 60s and 70s (Alperin et al, 2013; Cabeza et al, 2002; Curran et al, 2001; Hahn et al, 2011; Looren de Jong et al, 1988; Lorenzo-Lopez et al, 2007; Vallesi, Stuss, McIntosh, & Picton, 2009), leaving open questions about when in the lifespan dedifferentiation begins and whether it continues to progress in oldold age. Third, most prior studies have not explicitly tried to match different age groups in terms of cognitive capacity or performance on the experimental task (Curran et al, 2001; Hahn et al, 2011; Looren de Jong et al, 1988), making it problematic to interpret whether differences in neural activity between groups were due to age or other factors such as executive capacity, perceived task difficulty, or task performance.…”