The spatial window of the perceptual template and endogenous attention.

One primary function of spatial attention is to exclude external noise [e.g., Psychol. Sci. 11(2) (2000) 139], especially in the region of the target stimulus [J. Vis. 2(4) (2000) 312]. What is not known is the spatial profile of external noise exclusion in the vicinity of the target and how this depends upon attention. The spatial region around an oriented Gabor target was segmented into four concentric rings (R1-R4). Psychometric functions were measured for orientation discrimination with external random Gaussian noise in all combinations of rings (e.g., R1 alone; R1+R2; etc.). Regions with larger impact on performance are weighted more heavily in the perceptual template. In an orientation discrimination task in periphery the effective noise regions aligned closely with the high contrast regions of the target Gabor, with attention reducing the effective noise across the spatial template. The combined effects of external noise regions were well-modeled by a (non-linear) perceptual template model (PTM) [Vis. Res. 38(9) (1998) 1183]. In another experiment in attended fovea, the results were similar to those in periphery, but exhibited additional ability to selectively weight clear spatial regions.