Attentional modulation of lateral interactions depends on eccentricity

Visual attention has been found to facilitate texture segmentation in periphery by increasing spatial resolution (Yeshurun and Carrasco, 1998 Nature 396 72 - 75). Campana and Casco (2005 Perception 34 Supplement, this issue) show that attention not only increases spatial resolution but also reduces the effect of inhibitory short-range spatial interactions only in periphery. Casco et al (2005 Vision Research 45 2384 - 2396) found that attention produces a specific facilitation of texture segmentation when texture elements are oriented as the texture boundary (iso-oriented), probably resulting in enhancement of spatial interaction between texture elements. Is this modulation of facilitation by attention dependent on eccentricity? By using a RSVP paradigm, we manipulated, at 0 and 5 deg of eccentricity, the amount of attention allocated to orientation discrimination of a 3-Gabor-group, either horizontal or vertical, in which individual Gabors were either iso-oriented or ortho-oriented and differed by 45° in orientation from background Gabors. Our results show that when attentional resources are largely available, orientation discrimination of the iso-oriented group is facilitated both in fovea and in periphery. In contrast, the reduction of attention has different effects depending on eccentricity: a larger decrease in performance for iso-oriented than ortho-oriented groups in fovea, and a decrease in performance with ortho-oriented groups only, in periphery. Furthermore, whereas in periphery iso-oriented groups are far better discriminated than ortho-oriented ones, in fovea this difference is strongly reduced. These results indicate that in fovea attention is more engaged in grouping iso-oriented elements, whilst in the periphery only grouping of ortho-oriented elements needs attention. Overall, these results suggest that attention affects the strength of lateral interactions differently in fovea and periphery: reducing attention in the fovea reduces the strength of facilitatory lateral interactions between both iso-oriented and ortho-oriented Gabors, whereas in the periphery only the strength of facilitatory interactions between ortho-oriented Gabors is reduced.