Fig. 1.

Effects of distracters on grating orientation discrimination. (A) Example display sequence used in the orientation discrimination task. Observers fixated a central point throughout all trials. Lateralized target gratings appeared with/without distractor discs (shown here with distracters). Stimuli appeared briefly within the left or right visual field. observers were required to discriminate whether the grating was tilted to the left or right of vertical. In experiment 1, target orientation thresholds for each observer were calculated at 4 levels of distractor disk contrast (−50%, 0%, +50%, 80%). Distractor contrast was manipulated by changing disk luminance relative to the background (see Methods). (B) Orientation discrimination performance as a function of distracter contrast for pulvinar-lesioned patients and controls. Data represent mean (SE) change in orientation threshold from baseline. Data points in each graph are averages based on 4–6 thresholds. Performance in the “zero-contrast” distracter condition (baseline) is indicated by the dotted line. Examples of the 4 distractor conditions are illustrated above the graph. Open squares, patients; filled squares, controls. (C) Mean (SE) change in orientation threshold from baseline plotted separately for patients D.G. (Top), C.R. (Middle), and T.N. (Bottom). Data are plotted separately for targets appearing within the contralesional (filled squares) and ipsilesional (open squares) fields.