Abstract
Background: Performance fields are disparities at iso-eccentric locations in the visual field in detection, discrimination, localization, and information accrual, with best performance on the horizontal meridian and worst in the upper vertical meridian. Covert attention improves discriminability to a similar degree at iso-eccentric locations, leaving spatial performance field asymmetries intact (Carrasco et al., 2001, 2002), but eliminates temporal asymmetries (Carrasco et al., 2003). We have characterized the influence of temporal performance fields on the perception of illusory line motion. Perception of the illusion increased in correspondence with performance field differences, both of which were attenuated by covert attention (Santella & Carrasco, 2003). Here we examined the effect of these temporal asymmetries on another perceptual task — temporal order judgment. Methods: Observers judged the temporal precedence of two target patches whose onsets were separated by a variable delay period (0 to 150 ms), appearing at the same eccentricity in the upper (N) and lower (S) visual field along the vertical meridian. Targets were preceded either by a central neutral cue (at fixation) or a peripheral cue (adjacent to a single target). Observers performed a 2AFC task, indicating whether the top or bottom target was displayed last. Results & Conclusion: Consistent with the temporal performance field asymmetries (a) in the neutral cue condition, the point of subjective simultaneity (PoSS) was shifted so that the top target had to precede the bottom in order for them to be perceived as occurring at the same time. (b) The effect of N vs. S cue varied in the predicted direction, with a greater relative shift of the PoSS for the N than the S cue. These results are consistent with the claim that attention speeds information accrual, minimizing temporal performance field asymmetries (Carrasco et al., 2003) and they demonstrate the perceptual consequences of these disparities.
NSF grant #BCS-9910734/HCP