The dissociation between early and late selection in older adults

Modern neurophysiological techniques indexing normal or abnormal brain aging

Brain aging is associated with a decline in cognitive performance, motor function and sensory perception, even in the absence of neurodegeneration. The underlying pathophysiological mechanisms remain incompletely understood, though alterations in neurogenesis, neuronal senescence and synaptic plasticity are implicated. Recent years have seen advancements in neurophysiological techniques such as electroencephalography (EEG), magnetoencephalography (MEG), event-related potentials (ERP) and transcranial magnetic stimulation (TMS), offering insights into physiological and pathological brain aging. These methods provide real-time information on brain activity, connectivity and network dynamics. Integration of Artificial Intelligence (AI) techniques promise as a tool enhancing the diagnosis and prognosis of age-related cognitive decline. Our review highlights recent advances in these electrophysiological techniques (focusing on EEG, ERP, TMS and TMS-EEG methodologies) and their application in physiological and pathological brain aging. Physiological aging is characterized by changes in EEG spectral power and connectivity, ERP and TMS parameters, indicating alterations in neural activity and network function. Pathological aging, such as in Alzheimer's disease, is associated with further disruptions in EEG rhythms, ERP components and TMS measures, reflecting underlying neurodegenerative processes. Machine learning approaches show promise in classifying cognitive impairment and predicting disease progression. Standardization of neurophysiological methods and integration with other modalities are crucial for a comprehensive understanding of brain aging and neurodegenerative disorders. Advanced network analysis techniques and AI methods hold potential for enhancing diagnostic accuracy and deepening insights into age-related brain changes.

Aging impairs reactive attentional control but not proactive distractor inhibition

Older adults tend to be more prone to distraction compared with young adults, and this age-related deficit has been attributed to a deficiency in inhibitory processing. However, recent findings challenge the notion that aging leads to global impairments in inhibition. To reconcile these mixed findings, we investigated how aging modulates multiple mechanisms of attentional control by tracking the timing and direction of eye movements. When engaged in feature-search mode and proactive distractor suppression, older adults made fewer first fixations to the target but inhibited the task-irrelevant salient distractor as effectively as did young adults. However, when engaged in singleton-search mode and required to reactively disengage from the distractor, older adults made significantly more first saccades toward the task-irrelevant salient distractor and showed increased fixation times in orienting to the target, longer dwell times on incorrect saccades, and increased saccadic reaction times compared with young adults. Our findings reveal that aging differently impairs attentional control depending on whether visual search requires proactive distractor suppression or reactive distractor disengagement. Furthermore, our oculomotor measures reveal both age-related deficits and age equivalence in various mechanisms of attention, including goal-directed orienting, selection history, disengagement, and distractor inhibition. These findings help explain why conclusions of age-related declines or age equivalence in mechanisms of attentional control are task specific and reveal that older adults do not exhibit global impairments in mechanisms of inhibition. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Age Effects on Distraction in a Visual Task Requiring Fast Reactions: An Event-Related Potential Study

We investigated the effects of distractors in older and younger participants in choice and simple reaction time tasks with concurrent registration of event-related potentials. In the task the participants had to prevent a disk from falling into a bin after a color or luminosity change (target stimuli). Infrequently, task-irrelevant stimuli (schematic faces or threatening objects) were superimposed on the target stimuli (distractors), or the bin disappeared which required no response (Nogo trials). Reaction time was delayed to the distractors, but this effect was similar in the two age groups. As a robust age-related difference, in the older group a large anterior positivity and posterior negativity emerged to the distractors within the 100-200 ms post-stimulus range, and these components were larger for schematic faces than for threatening objects. sLORETA localized the age-specific effect to the ventral stream of the visual system and to anterior structures considered as parts of the executive system. The Nogo stimuli elicited a late positivity (Nogo P3) with longer latency in the older group. We interpreted the age-related differences as decreased but compensated resistance to task-irrelevant change of the target stimuli.

Capacity-limited resources are used for managing sensory degradation and cognitive demands: Implications for age-related cognitive decline and dementia

Older adults with sensory deficits are at higher risk for developing cognitive impairment and dementia. It remains uncertain if the link between sensory and cognitive functioning reflects a common underlying factor or whether sensory deficits directly undermine cognitive processing. This issue was addressed by comparing behavioral and event-related potential responses of 16 older and 16 young adults during a working memory paradigm that parametrically varied visual contrast level (100%, 69%, 22%) and cognitive task load (1-4 face pairs to remember). The groups were well-matched on demographic and neuropsychological variables; however, older adults had worse corrected visual acuity and contrast sensitivity. The study's major finding was an interaction between visual contrast level and task load on performance accuracy (percent of correct responses) and the allocation of resources for decision making/updating (as indexed by the P3b amplitude). The negative impact of degraded visual processing was greater at higher levels of task demand. This result suggests that a shared pool of processing resources is used to mediate cognitive operations and manage the processing of degraded images. The study also demonstrated that older adults reach the limits of their processing capacity at lower levels of task load. The interaction between visual degradation and task demand, accompanied by the age-related reduction in available processing resources highlight the increased vulnerability of older adults. Specifically, an age-associated decline in visual acuity and contrast sensitivity puts older adults at risk for depleting their limited resources in the service of processing degraded visual images. The results of this study underscore the potential importance of optimizing vision in older adults to help mitigate age-associated cognitive decline.

Multiple identity tracking strategies vary by age: An ERP study

Top-down modulation underlies our ability to focus attention on task-relevant stimuli and ignore irrelevant distractions. Although age-related differences in neural correlates of top-down modulation have been investigated in multiple studies using variety of tasks (Gazzaley et al., 2005; Störmer et al., 2013), the effect of age on top-down modulation in a multiple identity tracking (MIT) task is still unknown. Thus, we investigated age-related differences in the MIT task by employing event-related potentials (ERPs). Participants tracked ten uniquely colored disks, two of which were randomly designated as targets at the beginning of each trial; the targets moved among four stationary distractors (serving as ERP baseline) and four moving distractors. Each type of stimulus was probed during the trial to capture differential patterns of brain activation. Tracking performance was similar across age groups. ERP data showed that younger adults performed the MIT task by enhancing the unique identities associated with targets relative to distractors through feature-based tracking. Older adults showed a pattern of distractor suppression engaging both location- and feature-based tracking strategies. Thus, our findings suggest that compared to younger adults, older adults engage greater levels of neural activity to achieve the same level of performance. These findings are discussed in light of theories of cognitive aging.

Assessing cross-modal target transition effects with a visual-auditory oddball

Prior research has shown contextual manipulations involving temporal and sequence related factors significantly moderate attention-related responses, as indexed by the P3b event-related-potential, towards infrequent (i.e., deviant) target oddball stimuli. However, significantly less research has looked at the influence of cross-modal switching on P3b responding, with the impact of target-to-target cross-modal transitions being virtually unstudied. To address this gap, this study recorded high-density (256 electrodes) EEG data from twenty-five participants as they completed a cross-modal visual-auditory oddball task. This task was comprised of unimodal visual (70% Nontargets: 30% Deviant-targets) and auditory (70% Nontargets: 30% Deviant-targets) oddballs presented in fixed alternating order (i.e., visual-auditory-visual-auditory, etc.) with participants being tasked with detecting deviant-targets in both modalities. Differences in the P3b response towards deviant-targets as a function of preceding deviant-target's presentation modality was analyzed using temporal-spatial PCA decomposition. In line with predictions, the results indicate that the ERP response to auditory deviant-targets preceded by visual deviant-targets exhibits an elevated P3b, relative to the processing of auditory deviant-targets preceded by auditory deviant-targets. However, the processing of visual deviant-targets preceded by auditory deviant-targets exhibited a reduced P3b response, relative to the P3b response towards visual deviant-targets preceded by visual deviant-targets. These findings provide the first demonstration of temporally and perceptually decoupled target-to-target cross-modal transitions moderating P3b responses on the oddball paradigm, generally providing support for the context-updating interpretation of the P3b response.

On the use of the P300 as a tool for cognitive processing assessment in healthy aging: A review

Changes in patterns of performance for the cognitive functions of memory, processing speed, and focused attention are expected in old age.

An exploratory high-density EEG investigation of the misinformation effect: Attentional and recollective differences between true and false perceptual memories

The misinformation effect, a phenomenon in which eyewitness memories are altered via exposure to post-event misinformation, is one of the most important paradigms used to investigate the reconstructive nature of human memory. The aim of this study was to use the misinformation effect paradigm to investigate differences in attentional and recollective processing between true and false event memories. Nineteen participants completed a variant of the misinformation paradigm in which recognition responses to true and misinformation based event details embedded within a narrative context, were investigated using high-density (256-channel) EEG with a 1-day delay between event exposure and test. Source monitoring responses were used to isolate event-related-potentials (ERPs) associated with perceptual (i.e. event) source attributions. Temporal-spatial analyses of these ERPs showed evidence of an elevated P3b and Late-Positive Component, associated with stronger context-matching responses and recollective activity respectively, in true perceptual memories relative to false misinformation based ones. These findings represent the first retrieval focused EEG investigation of the misinformation effect and highlight the interplay between attention and retrieval processes in episodic memory recognition.

Increased Early Processing of Task-Irrelevant Auditory Stimuli in Older Adults

The inhibitory deficit hypothesis of cognitive aging posits that older adults' inability to adequately suppress processing of irrelevant information is a major source of cognitive decline. Prior research has demonstrated that in response to task-irrelevant auditory stimuli there is an age-associated increase in the amplitude of the N1 wave, an ERP marker of early perceptual processing. Here, we tested predictions derived from the inhibitory deficit hypothesis that the age-related increase in N1 would be 1) observed under an auditory-ignore, but not auditory-attend condition, 2) attenuated in individuals with high executive capacity (EC), and 3) augmented by increasing cognitive load of the primary visual task. ERPs were measured in 114 well-matched young, middle-aged, young-old, and old-old adults, designated as having high or average EC based on neuropsychological testing. Under the auditory-ignore (visual-attend) task, participants ignored auditory stimuli and responded to rare target letters under low and high load. Under the auditory-attend task, participants ignored visual stimuli and responded to rare target tones. Results confirmed an age-associated increase in N1 amplitude to auditory stimuli under the auditory-ignore but not auditory-attend task. Contrary to predictions, EC did not modulate the N1 response. The load effect was the opposite of expectation: the N1 to task-irrelevant auditory events was smaller under high load. Finally, older adults did not simply fail to suppress the N1 to auditory stimuli in the task-irrelevant modality; they generated a larger response than to identical stimuli in the task-relevant modality. In summary, several of the study's findings do not fit the inhibitory-deficit hypothesis of cognitive aging, which may need to be refined or supplemented by alternative accounts.

Increasing Working Memory Load Reduces Processing of Cross-Modal Task-Irrelevant Stimuli Even after Controlling for Task Difficulty and Executive Capacity

The classic account of the load theory (LT) of attention suggests that increasing cognitive load leads to greater processing of task-irrelevant stimuli due to competition for limited executive resource that reduces the ability to actively maintain current processing priorities. Studies testing this hypothesis have yielded widely divergent outcomes. The inconsistent results may, in part, be related to variability in executive capacity (EC) and task difficulty across subjects in different studies. Here, we used a cross-modal paradigm to investigate whether augmented working memory (WM) load leads to increased early distracter processing, and controlled for the potential confounders of EC and task difficulty. Twenty-three young subjects were engaged in a primary visual WM task, under high and low load conditions, while instructed to ignore irrelevant auditory stimuli. Demands of the high load condition were individually titrated to make task difficulty comparable across subjects with differing EC. Event-related potentials (ERPs) were used to measure neural activity in response to stimuli presented in both the task relevant modality (visual) and task-irrelevant modality (auditory). Behavioral results indicate that the load manipulation and titration procedure of the primary visual task were successful. ERPs demonstrated that in response to visual target stimuli, there was a load-related increase in the posterior slow wave, an index of sustained attention and effort. Importantly, under high load, there was a decrease of the auditory N1 in response to distracters, a marker of early auditory processing. These results suggest that increased WM load is associated with enhanced attentional engagement and protection from distraction in a cross-modal setting, even after controlling for task difficulty and EC. Our findings challenge the classic LT and offer support for alternative models.

Investigating age-related changes in anterior and posterior neural activity throughout the information processing stream

Event-related potential (ERP) and other functional imaging studies often demonstrate age-related increases in anterior neural activity and decreases in posterior activity while subjects carry out task demands. It remains unclear whether this "anterior shift" is limited to late cognitive operations like those indexed by the P3 component, or is evident during other stages of information processing. The temporal resolution of ERPs provided an opportunity to address this issue. Temporospatial principal component analysis (PCA) was used to identify underlying components that may be obscured by overlapping ERP waveforms. ERPs were measured during a visual oddball task in 26 young, 26 middle-aged, and 29 old subjects who were well-matched for IQ, executive function, education, and task performance. PCA identified six anterior factors peaking between ∼140 ms and 810 ms, and four posterior factors peaking between ∼300 ms and 810 ms. There was an age-related increase in the amplitude of anterior factors between ∼200 and 500 ms, and an age-associated decrease in amplitude of posterior factors after ∼500 ms. The increase in anterior processing began as early as middle-age, was sustained throughout old age, and appeared to be linear in nature. These results suggest that age-associated increases in anterior activity occur after early sensory processing has taken place, and are most prominent during a period in which attention is being marshaled to evaluate a stimulus. In contrast, age-related decreases in posterior activity manifest during operations involved in stimulus categorization, post-decision monitoring, and preparation for an upcoming event.

The impact of executive capacity and age on mechanisms underlying multidimensional feature selection

This study examined the role of executive capacity (EC) and aging in multidimensional feature selection. ERPs were recorded from healthy young and old adults of either high or average EC based on neuropsychological testing. Participants completed a color selective attention task in which they responded to target letter-forms in a specified color (attend condition) while ignoring letter-forms in a different color (ignore condition). Two selection negativity (SN) components were computed: the SN(Color) (attend-ignore), indexing early color selection, and the SN(Letter) (targets-standards), indexing early letter-form selection. High EC subjects exhibited self-terminating feature selection; the processing of one feature type was reduced if information from the other feature type suggested the stimulus did not contain the task-relevant feature. In contrast, average EC subjects exhaustively selected all features of a stimulus. The self-terminating approach was associated with better task accuracy. Higher EC was also linked to stronger early selection of target letter-forms, but did not modulate the seemingly less demanding task of color selection. Mechanisms utilized for multidimensional feature selection appear to be consistent across the lifespan, although there was age-related slowing of processing speed for early selection of letter features. We conclude that EC is a critical determinant of how multidimensional feature processing is carried out.

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

One mechanism hypothesized to contribute to cognitive aging is the failure to recruit specialized neural modules and generate differentiated neural responses to various classes of stimuli. Here, ERPs were used to examine the extent to which target and standard stimulus types were processed differently by well-matched adults ages 19-99. Subjects responded to designated visual target letters under low and high load conditions. Temporospatial PCA was used to parse the P3b component, an index of categorization/memory updating. The P3b amplitude difference between targets and standards decreased substantially as a function of age. Dedifferentiation began in middle age, and continued into old-old age. The reduced differentiation of neural responses was driven by an age-related decline in the size of the P3b to targets and an age-related increase in the P3b to standards. Larger P3b amplitude to standards among older subjects was associated with higher executive capacity and better task performance. In summary, dedifferentiation begins relatively early in adulthood and progresses in a linear fashion throughout the lifespan. The age-related augmentation of the P3b to standards appears to reflect a compensatory mechanism that helps maintain task performance.

Investigating the age-related "anterior shift" in the scalp distribution of the P3b component using principal component analysis

An age-related "anterior shift" in the distribution of the P3b is often reported. Temporospatial principal component analysis (PCA) was used to investigate the basis of this observation. ERPs were measured in young and old adults during a visual oddball task. PCA revealed two spatially distinct factors in both age groups, identified as the posterior P3b and anterior P3a. Young subjects generated a smaller P3a than P3b, while old subjects generated a P3a that did not differ in amplitude from their P3b. Rather than having a more anteriorly distributed P3b, old subjects produced a large, temporally overlapping P3a. The pattern of the age-related "anterior shift" in the P3 was similar for target and standard stimuli. The increase in the P3a in elderly adults may not represent a failure to habituate the novelty response, but may reflect greater reliance on executive control operations (P3a) to carry out the categorization/updating process (P3b).

Age-related differences in the automatic processing of single letters: implications for selective attention

Older adults exhibit diminished ability to inhibit the processing of visual stimuli that are supposed to be ignored. The extent to which age-related changes in early visual processing contribute to impairments in selective attention remains to be determined. Here, 103 adults, 18-85 years of age, completed a color selective attention task in which they were asked to attend to a specified color and respond to designated target letters. An optimal approach would be to initially filter according to color and then process letter forms in the attend color to identify targets. An asymmetric N170 ERP component (larger amplitude over left posterior hemisphere sites) was used as a marker of the early automatic processing of letter forms. Young and middle-aged adults did not generate an asymmetric N170 component. In contrast, young-old and old-old adults produced a larger N170 over the left hemisphere. Furthermore, older adults generated a larger N170 to letter than nonletter stimuli over the left, but not right hemisphere. More asymmetric N170 responses predicted greater allocation of late selection resources to target letters in the ignore color, as indexed by P3b amplitude. These results suggest that unlike their younger counterparts, older adults automatically process stimuli as letters early in the selection process, when it would be more efficient to attend to color only. The inability to ignore letters early in the processing stream helps explain the age-related increase in subsequent processing of target letter forms presented in the ignore color.