Eccentricity Constrains Spatial Working Memory Fidelity: Evidence for the Cortical Maps Hypothesis

Spatial working memory (SWM) has been characterized as a flexible resource that determines the precision with which memoranda are stored. The ‘cortical map’ proposal predicts that resource allocation, and therefore mnemonic precision, is limited by the availability of cortical space to represent memoranda. This hypothesis was tested using a continuous spatial localization task in which memory items were presented at 3 eccentricities and set sizes of 1- 8. Localization error increased systematically with eccentricity, and this effect became larger as set size increased. Mixture-modelling analyses revealed that the eccentricity effect was primarily driven by increases in imprecision at small set sizes (set sizes 1-4). In contrast, when set size exceeded five items, guessing became an increasingly important contributor to localization error, suggesting that representations of peripheral locations become more vulnerable to memory failure under high memory loads. Misbinding errors were most prominent for locations nearest fixation, likely reflecting reduced inter-item spacing at small eccentricities. Stimuli were not scaled to compensate for cortical magnification, but the observed increase in imprecision closely matched predictions derived from a cortical magnification function. Together, these findings support the cortical maps hypothesis and indicate that spatial working memory representations compete for limited representational resources within the spatial maps that guide action.