Attraction of population receptive fields is determined by precision of attention

Abstract

Spatial attention enhances perception at attended locations. Population receptive fields (pRFs) are attracted to the position of the attentional locus, yet how the precision of attention influences pRF properties remains to be investigated. The attention field model, often used to summarize the locus of attention by a Gaussian field, predicts that attentional precision (Gaussian standard deviation) should influence pRF properties. Here, we investigated the effect of spatial precision of attention on pRF properties while keeping the attended location constant. We measured pRFs using ultra-high field 7T MRI while participants performed a color discrimination task. Two attention conditions were compared: attention narrowed on fixation (0.1 deg) and attention maximally distributed across the entire screen (>5 deg). In both conditions the same visual stimulus was presented and only the spatial extent of attention varied. The stimulus contained a standard pRF mapping contrast-defined bar. The narrow attention and distributed attention conditions did not differ in task difficulty and participants successfully modulated their spatial distribution of attention. The task elicited eccentricity-dependent changes in BOLD baseline in early visual areas. In particular, higher foveal BOLD responses to the narrow attention task and higher peripheral BOLD responses to the distributed attention task were observed. As predicted by the attention field model, pRF positions were altered as a function of attentional precision, with stronger attraction of pRF position towards the attended locus in the narrow attention condition. Moreover, larger pRF position changes were observed with increasing pRF size up the visual hierarchy. In addition to pRF position changes, attentional precision also influenced pRF size, with increased pRF size differences in higher visual areas. These results indicate that the size of spatial attention dynamically alters pRF properties in a manner consistent with the predictions of the attention field model.