Visual field map size constrains working memory precision.

Individual differences in working memory are associated with cognitive functioning and real-world outcomes, including general intelligence, academic achievement, and psychiatric and neurological disorders. Despite its importance, the neurobiological mechanisms that drive individual differences in working memory are unknown. Here, we asked whether the precision of spatial working memory covaries with the cortical surface area of retinotopically organized maps that are thought to store the content of working memory. In particular, we hypothesized that individuals with larger visual field maps would have more precise working memory. We assessed human subjects' (male and female) working memory precision using a memory-guided saccade task, and using fMRI we separately mapped retinotopically organized regions of visual, parietal, and frontal cortex. In support of our hypothesis, we found that people with larger maps in primary visual cortex and parietal cortex had better memory. To test hypotheses about the potential mechanisms driving our results, we simulated working memory in neural network models with varying numbers of synthetic neurons. Echoing our empirical results, larger networks exhibited less memory error. This reduction in error could be fully attributed to a decrease in the proportion of memory-perturbing noise along the attractor in larger networks, establishing a pure size effect on working memory precision.