Visual search for apparent-length targets is modulated by the Müller-Lyer illusion.
Is apparent object size represented in pre-attentive vision and can it influence visual search for size-defined targets in a spatially parallel manner? This question was investigated, using the Müller-Lyer illusion. Observers searched for a target line that was longer than the distractor lines. Test lines could be presented without context arrows (control); be adjoined by obtuse-angle context arrows (arrow heads pointing inward), making the lines appear longer; or by acute-angle arrows (heads pointing outward), making the lines appear shorter. These apparent-length modulations were larger for the target than for the distractor lines, thereby increasing and, respectively, decreasing the target-distractor length contrast. In line with these changes in contrast, target detection was found to be expedited by obtuse-angle arrows and impeded by acute-angle arrows, independently of the number of elements in the display. This finding provides further evidence for the pre-attentive processing of apparent object size.
Busch
Astrid
A
Department of Psychology, Ludwig-Maximilians-University, Munich, Germany. abusch@psy.uni-muenchen.de
Müller
Hermann J
HJ
D000328:Adult; D001288:Attention; D005260:Female; D005556:Form Perception; D006801:Humans; D008297:Male; D009903:Optical Illusions; D013028:Space Perception; D014785:Vision, Ocular