Laure Pisella¹, Tristan Jurkiewicz¹, Yaffa Yeshurun²; ¹Centre de Recherche en Neuroscience de Lyon, ²University of Haifa

The Superior Parietal Lobule (SPL) is an associative area that is part of two identified functional systems: the dorsal visual pathway and the dorsal covert attention network. The dual visual pathway theory proposed that the occipito-parietal pathway is involved in mechanisms of "vision for action" but not in those of "vision for perception", highlighting that patients with optic ataxia (OA) are impaired for reach-to-grasp movements after SPL damage. More precise and recent investigations have shown that the visuo-motor impairments in OA are characterized by pointing errors in peripheral vision, underestimating the visual eccentricity of targets. Additionally, OA patients display, in their affected peripheral visual field, a perceptual underestimation of object size, and a deficit of covert attention revealed by slower visual processing despite valid cueing. We hypothesized that most of the deficits observed in OA patients in their contralesional visual field stem from a common dysfunction in the dorsal covert attention network, of which the SPL is a part. In two experiments we investigated the nature of peripheral pointing errors in the absence of covert spatial attention using a pointing task combined with central high-predictive and peripheral low-predictive attentional precues. These cues either indicated the correct pointing target location or a different location. We observed pointing errors mimicking the target position underestimations typical of OA through invalid endogenous cueing in control subjects. Moreover, in OA patients, valid cueing improved peripheral target-pointing performance. Low-predictive cues affected RT but not pointing accuracy. In a third experiment, we used similar predictive cues to modulate the perceived size of peripheral objects in control subjects. We found that invalid endogenous cueing shifted the responses toward a perceptual underestimation of object size. According to these results, we propose that SPL-based endogenous attention counteracts cortical magnification—i.e. actively re-magnifies the representation of the peripheral field.

Acknowledgements: This work has been supported by Fondation Neurodis. No commercial interests and conflicts to declare.