The Relationship Between Intelligence, Working Memory Capacity and Information Processing Speed During Encoding

The mental speed hypothesis of intelligence proposes that individual differences in intelligence arise from variations in the information processing speed (IPS). However, studies using reaction times to investigate this relationship show only low to moderate correlations (Sheppard & Vernon, 2008). To obtain more precise measures of mental speed, researchers have analyzed the latencies of event-related potential (ERP) components associated with higher-order cognitive processes, providing strong evidence for the mental speed account with latent correlations ranging from -.49 to -.89 (Schubert et al., 2017, 2023). However, it remains unclear to what extent the relationship between speed and intelligence is specific to decision-related processes or also holds true for non-decisional working memory (WM) processes. In this study, we take an integrative approach to (1) evaluate the generalizability of the relationship between IPS and intelligence with regard to the speed of WM encoding, and (2) extend previous research by examining the role of WM capacity (WMC). To this end, we collected data on EEG measures, WMC, and intelligence from 141 participants and analyzed latent correlations using a latent state-trait model to account for measurement error and situation-specific variance. Our results indicate that IPS during WM encoding, as measured by the latencies of late ERP components, is not significantly related to intelligence or WMC. These findings suggest that the relationship between mental speed and intelligence depends on factors that warrant further investigation.