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Age‐Related Differences in Response Time Across Adolescence Reflect Premotor, but Not Motor, Processing Speed
Journal article   Open access   Peer reviewed

Age‐Related Differences in Response Time Across Adolescence Reflect Premotor, but Not Motor, Processing Speed

William Slawson, Greg Hajcak, Bob McMurray and Bruce D. Bartholow
Psychophysiology, Vol.63(5), e70313
05/01/2026
DOI: 10.1111/psyp.70313
PMID: 42093089
Appears in  UI Libraries Support Open Access
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https://doi.org/10.1111/psyp.70313View
Published (Version of record) Open Access

Abstract

Extant literature suggests that developmental improvements in processing speed reflect changes in a common global processing factor. In theory, then, the influence of age on processing speed should be shared across premotor processes (e.g., response selection) and motor processes (e.g., response execution). However, some researchers have observed differences in the effect of age on speed across different processes depending on stage of development, and research on neurodevelopment has long demonstrated variation in the developmental trajectory of cortical regions associated with different functions. The current study explored whether age‐related differences in processing speed during adolescence varied between premotor and motor domains, testing whether these domain‐specific differences accounted for age‐related variance in choice reaction time (RT). Adolescent participants (N = 204, 68.6% female) varying in age from 14 to 19 years (M age = 16, SDage = 1.73) completed a flanker task while EEG was recorded. We quantified the lateralized readiness potential (LRP) to fractionate RTs into premotor (stimulus‐locked LRP [S‐LRP]) and motor (response‐locked LRP [R‐LRP]) intervals. Both S‐LRP and R‐LRP latencies correlated with RT, but only S‐LRP latency decreased with age. Mediation analysis confirmed a significant indirect effect of age on RT through S‐LRP latency but not R‐LRP latency, suggesting that faster processing speed among older adolescents stems from faster premotor—but not motor—processing. We demonstrate the utility of using LRP latencies to investigate domain‐specific processing speed, highlighting directions for future work to link structural development research to functional measurements. This study uses a novel ERP approach to challenge the prevailing theory that all components of processing speed develop uniformly across adolescence, showing distinct age effects on premotor and motor speeds in a cross‐sectional design. Utilizing LRP onset latency to quantify speeds of distinct processes within a single task, the study demonstrates the utility of applying a psychophysiological method to studying mental chronometry in developmental contexts, bridging functional and structural accounts of adolescent brain development.
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