Investigating working memory capacity: stability, contextual cueing and attention

Abstract

Visual working memory (vWM) is a system responsible for temporarily storing visual information, yet its precise nature and capacity limits remain unclear. This thesis presents three studies examining whether vWM capacity is stable across perceptual conditions, can be increased through learned regularities and how it constrains the allocation of attention during search. Study 1 (Chapter 2) comprised five behavioural experiments manipulating perceptual parameters: stimulus density (Experiment 1), stimulus eccentricity (Experiment 2), stimulus organisation (Experiment 3), stimulus type (Experiment 4), and spatial variability of stimuli (Experiment 5). Absolute capacity estimates (K values) differed significantly across conditions but showed consistent individual differences. Study 2 (Chapter 3) comprised two electrophysiological experiments investigating the effects of implicit learning on vWM. Experiment 1 employed a change detection task with low vs. high memory load conditions. Results showed that repeated configurations led to higher K values and reduced contralateral delay activity (CDA) amplitudes. Experiment 2 compared visuospatial (colour-location) and non-spatial (colour-only) conditions, revealing that both K increases and CDA reductions were specific only to the visuospatial condition. Study 3 (Chapter 4) was a single electrophysiological experiment examining the relationship between vWM capacity and visual search performance. Results from change detection and search tasks revealed that individuals with higher vWM capacity exhibited greater search accuracy, stronger attentional selection, and reduced performance costs under higher search loads. Together, these studies demonstrate that VWM capacity is not fixed in absolute terms but is a reliable relative measure across individuals. This work advances our understanding of how vWM capacity interacts with perceptual context, implicit learning, and attentional control.