Intra-individual variability adaptively increases following inhibition training during middle childhood

Characterizing Cognitive Dispersion and Its Correlates Across the Adult Lifespan in MIDUS

OBJECTIVES

Although research has shown that higher levels of within-person variability across cognitive tasks (dispersion) are associated with cognitive decline in clinical samples, little is known about dispersion in comparatively younger, nonclinical, and national samples. A better understanding of dispersion is needed to elucidate for whom and under what circumstances dispersion can be used as a reliable indicator of cognitive health.

METHOD

We used data from the Midlife in the United States Study (MIDUS; n = 2,229; Mage = 56 years, range = 33-83; 56% female) to: (a) characterize dispersion and its cross-sectional correlates in a nonclinical, adult lifespan sample and (b) examine changes in dispersion over time to determine for whom changes in dispersion may reflect better or worse cognitive aging.

RESULTS

Correlations showed higher levels of dispersion were associated with higher levels of mean performance at both waves (rs = 0.28-0.29). Autoregressive main effect models showed that increases in dispersion were associated with less decline in mean performance over the 2-wave, 9-year follow-up period (β = 0.17, p < .001). Moderation models showed that the link between change in dispersion and change in mean performance was pronounced in comparatively older adults (β = 0.28), women (β = 0.27), individuals with less education (β = 0.23), and those with lower income (β = 0.23; all ps < .001).

DISCUSSION

Findings suggest that increases in dispersion may not always be maladaptive in normative, adult lifespan samples and may reflect healthier cognitive profiles in individuals who are at greater risk for cognitive impairment.

On the (un)reliability of common behavioral and electrophysiological measures from the stop signal task: Measures of inhibition lack stability over time

Response inhibition, the intentional stopping of planned or initiated actions, is often considered a key facet of control, impulsivity, and self-regulation. The stop signal task is argued to be the purest inhibition task we have, and it is thus central to much work investigating the role of inhibition in areas like development and psychopathology. Most of this work quantifies stopping behavior by calculating the stop signal reaction time as a measure of individual stopping latency. Individual difference studies aiming to investigate why and how stopping latencies differ between people often do this under the assumption that the stop signal reaction time indexes a stable, dispositional trait. However, empirical support for this assumption is lacking, as common measures of inhibition and control tend to show low test-retest reliability and thus appear unstable over time. The reasons for this could be methodological, where low stability is driven by measurement noise, or substantive, where low stability is driven by a larger influence of state-like and situational factors. To investigate this, we characterized the split-half and test-retest reliability of a range of common behavioral and electrophysiological measures derived from the stop signal task. Across three independent studies, different measurement modalities, and a systematic review of the literature, we found a pattern of low temporal stability for inhibition measures and higher stability for measures of manifest behavior and non-inhibitory processing. This pattern could not be explained by measurement noise and low internal consistency. Consequently, response inhibition appears to have mostly state-like and situational determinants, and there is little support for the validity of conceptualizing common inhibition measures as reflecting stable traits.