Attentional modulation of size perception in peripheral vision.

The perceived size of objects decreases with increasing eccentricity, a phenomenon known as the "size-eccentricity effect." This bias is thought to reflect cortical magnification: the overrepresentation of central vision relative to peripheral vision. Previous studies suggest that attention may influence this perceptual distortion, yet the specific contribution of endogenous attention remains debated. Here, we investigated whether endogenous attention attenuates or exacerbates the size-eccentricity effect. Ten healthy right-handed participants performed a size comparison task. On each trial, participants judged the size of a peripheral rectangle (presented at 8.9°, 15.6°, or 23.4° eccentricity) compared to a fixed central reference. Endogenous attention was manipulated using central arrow cues that predicted the location of the peripheral stimulus with 70% validity. Perceived size was quantified using psychometric functions to extract the point of subjective equivalence based on response accuracy or reaction time. As predicted by the size-eccentricity effect, participants systematically underestimated the size of peripheral relative to central objects. Importantly, this underestimation was significantly reduced in the valid cueing condition, particularly at greater eccentricities, indicating that endogenous attention attenuates the size-eccentricity effect. Attention also enhanced sensitivity, as shown by steeper psychometric slopes. These findings suggest that endogenous attention actively compensates for cortical magnification by "rescaling" peripheral representations, leading to better perceptual size accuracy and discriminability. In contrast, misallocation of attention increases peripheral underestimation, paralleling pathological biases in optic ataxia. We propose that dorsal parietal regions implement this attentional rescaling, supporting accurate perception and visuomotor transformations in peripheral vision.