Peter Neri^1,2; ¹Italian Institute of Technology, Erzelli Campus, Genova (Italy), ²Laboratoire des Systèmes Perceptifs, École Normale Supérieure, Paris (France)

When an object is attended, its characteristics are enhanced: for example, its apparent contrast increases. This phenomenological observation suggests that visual attention and contrast perception may share common perceptual mechanisms. We performed experiments in which these two phenomena were independently manipulated within the same experimental paradigm: contrast was manipulated by simply varying the contrast of the entire stimulus display; attention was manipulated via valid spatial cues that could appear either before or after the display. Our results confirm previous findings: at the zeroth order of characterization (measurements of performance and reliability), the two phenomena behave in similar manner (more contrast/attention leads to better performance); at the first order of characterization (measurements of linear filtering processes), they again behave in similar fashion (more contrast/attention leads to higher gain). However, when we examined these phenomena at the second order of characterization (measurements of nonlinear processes), we found that they behave in qualitatively different manners (more attention increases gain, while more contrast decreases gain). The observed differences are captured by a computational model in which visual stimuli are mapped to a perceptual surface, and the process of selecting a target is dictated by distance measurements on said surface. Within this framework, contrast manipulations vary the curvature of the surface, while attentional deployment modulates the degree of noisiness associated with traveling across the surface. Our results therefore point to two distinct mechanisms underlying attentional deployment and contrast perception: if we conceptualize perceptual decisions as agents exploring high-dimensional sensory representations, varying stimulus contrast alters the geometry of such representations, while attending to a stimulus increases the precision with which perceptual agents can track shortest paths across the representation.

Acknowledgements: Supported by IIT (grant IVXX000701), the Agence nationale de la recherche (grants ANR-16-CE28-0016, ANR-19-CE28-0010-01, ANR-10-LABX-0087, ANR-10-IDEX-0001-02, ANR-22-CE93-0013), and CNRS.