Effects of spatial location on distractor interference.

When target and distractor stimuli are close together, they activate the same neurons and there is ambiguity as to what the neural activity represents. It has been suggested that the ambiguity is resolved by spatial competition between target and nontarget stimuli. A competitive advantage is conveyed by bottom-up biases (e.g., stimulus saliency) and top-down biases (e.g., the match to a stored representation of the target stimulus). Here, we tested the hypothesis that regions with high perceptual performance may provide a bottom-up bias, resulting in increased distractor interference. Initially, we focused on two known anisotropies. At equal distance from central fixation, perceptual performance is better along the horizontal than the vertical meridian, and in the lower than in the upper visual hemifield. Consistently, interference from distractors on the horizontal meridian was greater than interference from distractors on the vertical meridian. However, distractors in the lower hemifield interfered less than distractors in the upper visual hemifield, which is contrary to the known anisotropy. These results were obtained with targets and distractors on opposite meridians. Further, we observed greater interference from distractors on the meridians compared with distractors on the diagonals, possibly reflecting anisotropies in attentional scanning. Overall, the results are only partially consistent with the hypothesis that distractor interference is larger for distractors on regions with high perceptual performance.