ASYMMETRIES IN PREATTENTIVE LINE DETECTION

We tested the relative contribution of absolute orientation and collin earity to asymmetries in preattentive line detection. Subjects reporte d the location of a single line that was tilted by 16 deg against the orientation of the background lines. Perceptual pop-out strength was q uantified as the threshold presentation time to correctly locate the s alient element. We found that (1) threshold times mere significantly s horter in vertical than in oblique background lines and that (2) thres hold times were significantly shorter in collinear than in non-colline ar background lines. Our data suggest that the sensitivity of preatten tive processes for orientation gradients is modulated by both collinea rity and absolute orientation.