Talgar, CP, Carrasco, M (2001, May). The effects of attention in texture segmentation in the lower and upper visual fields. Vision ScienceS Society, Sarasota, FL. 76-B9.

Abstract
Introduction. This study is based on two findings: 1) In a texture segmentation task, attending to the target location improved performance where the resolution is too low (periphery) but impaired it where resolution is already too high (central locations) for the task. These results indicate an enhanced spatial resolution at the attended location (Yeshurun & Carrasco, 1998). 2) In some tasks, performance is better across the horizontal than the vertical meridian - horizontal vertical anisotropy - and in lower than upper region of the vertical meridian - vertical meridian asymmetry (VMA). Whereas some attribute this "performance field" to attentional effects, Carrasco, Talgar & Cameron (in Press) showed that although transient attention enhances overall contrast sensitivity, the shape of the performance field does not change - performance fields are determined by visual factors.

Goal. Is there a VMA for spatial resolution? At equal eccentricities, does attention enhance spatial resolution to the same degree in the upper and lower regions of the vertical meridian?

Methods. In a texture segmentation task where performance peaks at mid-peripheral locations, the central performance drop is attributed to the spatial filters at the fovea being too small for the scale of the texture. In a 2IFC task observers were presented with a cue that either indicated the time of target onset (neutral cue: 50 % of trials) or indicated both time and location of target onset (peripheral cue: 50% of trials). The target patch appeared at varying eccentricities in a large texture pattern along the vertical meridian.

Results. 1) The central performance drop was larger and performance peaked at farther eccentricities in the lower than upper visual field. 2) Attention affected the visual field uniformly.

Conclusion. Resolution was higher on the lower half of the vertical meridian. The degree of enhanced resolution brought about by transient attention was constant along the vertical meridian.