Abstract
We previously showed that exogenous attention could be finely tuned within the fovea, enhancing visual discrimination at the attended location only arcminutes away from its distractors. Yet, it is unknown whether this effect is the result of a modulation of sensitivity across a wide range of spatial frequencies and if frequencies close to the resolution limit can also be enhanced. To examine this issue, after triggering exogenous attention at a specific location in the fovea, observers (N=4) were instructed to discriminate the orientation of a grating with spatial frequency varied from 4 to 20 CPD. Observers maintained fixation on a central marker throughout the trial. Tight fixation was ensured by monitoring gaze position with a high precision eye-tracker. An exogenous cue (100% validity) was presented at 0.75 deg eccentricity either on the left or right side of the display. Shortly after the cue disappeared, two small gabor patches (0.5 deg visible area), tilted +/- 45 degrees, were shown (50 ms) on the left and right side of fixation at 0.5 deg eccentricity. At the end of the trial, observers reported the orientation of the gabor that was presented at the location indicated by a response cue . Our findings show that high-resolution exogenous attention enhanced 12CPD stimuli the most, with an increase of 1.1 units of d’, compared to a baseline condition in which no attentional cue was presented. Yet, a clear effect of attention on visual discrimination was reported across all the spatial frequencies tested up to those close to the resolution limit (P < 0.0001). Different from what was previously reported when exogenous attention is globally allocated in the fovea, these findings show that the effects of fine-grained exogenous attention extend to a wide range of spatial frequencies.