Event-related brain potentials reveal strategy selection in younger and older adults

Abstract

It is well-established that younger adults prioritize information accrued during different stages of stimulus evaluation ("early" versus "late") to optimize performance. The extent to which older adults flexibly adjust their processing strategies, however, is largely unexplored. Twenty-four younger and twenty-four older participants completed a cued flanker task in which one of three cues, indicating the probability that a congruent array would appear (75 %, 50 %, or 25 %), was presented on each trial. Behavioral and ERP (CNV, LRP, N2, and P3b) analyses allowed us to infer cue-driven changes in strategy selection. Results indicate that when both younger and older adults expected an incongruent array, they prioritized late, target information, resulting in a decreased susceptibility to the performance-impairing effect of distractors, extending the conclusions of Gratton et al. (1992) to older adults and supporting the claim that strategic control remains largely intact during healthy aging.

Keywords: Aging; Cognitive control; Congruency effect (CE); Event related brain potentials (ERPs); Lateralized readiness potential (LRP).

Figure 1:

Trial schematic. Participants were instructed to press a button on one of two keypads that corresponded to the direction of the target (central) arrow (i.e., a left-pointing arrow required a left button press and vice versa). Participants were given nearly 2 seconds to respond, extending from the onset of the imperative stimulus to the beginning of the next trial. The International Affective Picture System (IAPS) catalog numbers for the images used as cues are 7018, 7100, and 7705 for the screw, fire hydrant, and dresser, respectively (a representative image is shown here: “Yellow Fire Hydrant” by Lee Edwin Coursey, licensed under CC BY 2.0). The presented cue varied randomly on a trial-by-trial basis.

Figure 2:

Grand average lateralized readiness potential (LRP) waveforms time-locked to target (flanker array) onset. Solid and dashed lines indicate the congruent and incongruent conditions, respectively, while red, green, and blue lines indicate the predict-congruent (PC), predict-equiprobable (PE), and predict-incongruent (PI) conditions, respectively.

Figure 3:

From top to bottom: Mean response time (RT), accuracy (ACC), and inverse efficiency score (IES = RT ÷ ACC) for each of the three cue types (PC, PE, PI) by age (younger — light colors, older — dark-colors) and congruency (congruent — solid, incongruent — striped). YA = younger adults; OA = older adults; Con = congruent; Inc = incongruent; PC = predict-congruent; PE = predict-equiprobable; PI = predict-incongruent.

Figure 4:

From top to bottom: Mean response time (RT), accuracy (ACC), and inverse efficiency score (IES = RT ÷ ACC) congruency effects (CE; incongruent minus congruent) for younger (light) and older adults (dark). YA = younger adults; OA = older adults; PC = predict-congruent; PE = predict-equiprobable; PI = predict-incongruent.

Figure 5:

Top: Grand average ERP waveforms time-locked to cue onset for younger (YA; solid lines) and older adults (OA; dashed lines). Red, green, and blue lines represent ERP waveforms elicited by predict-congruent (PC), predict-equiprobable (PE), and predict-incongruent (PI) cues, respectively. The interval encompassed by the black rectangle indicates the time window (1200–1498 ms) used to measure the mean amplitude of the contingent negative variation (CNV). Bottom: Topographic plots of mean CNV amplitude from 1200–1498 ms for younger (left column) and older adults (right column).

Figure 6:

Grand average lateralized readiness potential (LRP) congruency effect waveforms (CE; incongruent minus congruent) time-locked to target (flanker array) onset. Red, green, and blue lines indicate the predict-congruent (PC), predict-equiprobable (PE), and predict-incongruent (PI) conditions, respectively. For both younger and older adults, the early, positive-going (downward) deflection occurs when the difference in response activation levels on congruent trials (correct activation > incorrect activation) is larger (i.e., more negative) than the difference in response activation levels on incongruent trials (incorrect activation > correct activation). Rectangles indicate the time windows during which local peak amplitude measurements were taken (200–500 ms).

Figure 7:

(a) The mean lateralized readiness potential (LRP) amplitude congruency effect (CE; difference in amplitude between incongruent and congruent trials) for younger (light) and older adults (dark). (b) Average local peak N2 amplitudes and (c) average local peak P3b amplitudes for each of the three cue types (PC, PE, PI) by age (younger — light colors, older — dark-colors) and congruency (congruent — solid, incongruent — striped). YA = younger adults; OA = older adults; Con = congruent; Inc = incongruent; PC = predict-congruent; PE = predict-equiprobable; PI = predict-incongruent.

Figure 8:

Younger (solid lines) and older adults’ (dashed lines) grand average event-related potential (ERP) waveforms time-locked to target (flanker array) onset for congruent and incongruent trials (red and black lines), following predict-congruent (PC), predict-equiprobable (PE), and predict-incongruent (PI) cues at electrodes FCz (left column) and Pz (right column). Rectangles indicate the time windows during which local peak amplitude measurements were taken (200–500 ms and 300–700 ms at FCz and Pz, respectively).

Figure 9:

Topographic plots of N2 amplitude for each of the six conditions at their respective peak latencies, as listed under each plot, for younger adults (top) and older adults (bottom). PC = predict-congruent; PE = predict-equiprobable; PI = predict-incongruent.

Figure 10:

Topographic plots of P3b amplitude for each of the six conditions at their respective peak latencies, as listed under each plot, for younger adults (top) and older adults (bottom). PC = predict-congruent; PE = predict-equiprobable; PI = predict-incongruent.