Coactivation, pop-out, and symmetry affect line discrimination

17 college students discriminated between vertical and horizontal target lines flanked by vertical and horizontal distractors. Large displays with 3.0-cm lines and small displays half this size were used. The distractors were positioned above and below the target or to the left and right of it, forming vertical and horizontal global orientations. The number of flankers sharing the target's orientation was varied. Vertical targets and small display sizes were processed more quickly. Speed of responding did not differ for the two global orientations. There was no advantage for target lines consistent with global orientation. The results were replicated in Exp. 2 with diagonal flankers. This supports an explanation using stimulus compatibility, since diagonal lines do not correspond to either of the response options and cannot induce a tendency to respond more to one target than another. Displays with multiple symmetry were responded to faster than those with a single symmetry which were faster than asymmetrical displays, supporting the idea that symmetrical axes parallel and perpendicular to the target orientation provide a facilitative frame of reference. Coactivation from same-oriented flankers, pop-out from differences in orientation, and symmetry all influenced responding in these patterns.