Samantha Sartin¹, Domenico Dal Monte², Fabio Del Giudice¹, Laura Caleca², Elena Prosperi², Federica Carini², Federica Danaj³, Irene Sperandio², Simona Monaco¹; ¹Center for Mind/Brain Sciences, University of Trento, ²Department of Psychology and Cognitive Science, University of Trento, ³University of Regensburg

Human neuroimaging work shows that the foveal cortex is recruited during haptic exploration of objects, in the absence of visual input. Here we investigate whether haptic processing of object properties in the foveal cortex is relevant for behaviour. To this aim, we tested 30 individuals in a behavioral paradigm (Exp.1). Participants used their right-dominant hand to haptically explore one of three differently sized cylinders placed behind a monitor, while fixating a central cross. During the haptic exploration, dynamic visual noise (DVN) was presented in central vision (Noise condition) to disrupt haptic processing in the foveal cortex, if present. In a control condition, no DVN was present. Subsequently, participants were instructed to manually estimate the size of the explored stimulus. We then tested 34 volunteers (Exp.2) to investigate whether DVN effects on haptic size estimation may be explained by: 1) foveal processing, 2) the contribution of bimodal cells with overlapping visual and somatosensory receptive fields, 3) attentional distraction. To test these hypotheses, we adapted the previous behavioural paradigm such that in Noise trials the DVN randomly appeared in the center, on the right or left side of the screen. Results of Exp.1 show that size estimation is larger in the Noise as compared to the control condition, suggesting uncertainty when DVN is present. Further, standard deviations of size estimates increase with stimulus size, suggesting that haptic size processing, like visual processing, follows Weber's law. Results of Exp.2 reveal no significant effect of DVN location on performance, suggesting that none of the tested hypotheses can explain the results of Exp.1. While the results of Exp.1 suggest that the foveal cortex supports haptic size estimation, further research is needed to understand if the simultaneous interplay between multiple mechanisms could explain these results.

Acknowledgements: We thank Next Generation EU, MUR, and the University of Trento for their financial support.