Yi, D. -J., & Kim, M. -S. (1999). The line motion illusion in visual search. Korean Journal of Experimental & Cognitive Psychology, 11 (2), 171-184.

 

The Line Motion Illusion in Visual Search

Do-Joon Yi & Min-Shik Kim

Department of Psychology

Yonsei University, Seoul, Korea

 

When a line is preceded by a dot at one of its ends, the line is perceived to grow from the dot. It has been proposed that this illusory motion might result from the local facilitation of a line in the gradient of attention summoned by the dot (Hikosaka, Miyauchi, & Shimojo, 1993) or from the binding process between the dot and the line (Downing & Treisman, 1997). To test these hypotheses, we conducted dual-task experiments in which a line was preceded by visual search items. Subjects reported the direction of illusory motion while searching for a color-defined target (e.g., a red square), which was presented along with a distractor with a target feature (e.g., a green square) and a distractor without a target feature (e.g., a green diamond). The facilitation hypotheis predicts that a line would be perceived to grow from the target to the distractors, and also from the target-shape distractor to the nontarget-shape distractor. On the contrary, Experiment 1 showed no difference among search items in inducing illusory motion sensation (Experiment 1), which is compatible with the binding hypothesis. Experiment 2 replicated the results with a partial offset paradigm (Yantis & Jonides, 1984), excluding an alternative account that the sudden onset of search items might allow distractors to capture as much attention as a target. Experiment 3 measured the amount of attention in each search item location with a dot probe paradigm (Kim & Cave, 1995), confirming that attention was indeed deployed more to the target than to the distractors and more to the target-shape distractor than to the nontarget-shape distractor. Our findings demonstrate that attention is not sufficient for the line motion illusion and suggest that spatial attention plays a role of binding visual objects (Treisman, 1988).
Figure 1. Schematic trial sequence in Experiment 1. In this example, a subject searched for a red item as target to report its shape. A line followed search items only in a half of trials. The example of probe trials here shows a condition in which a line was presented between the locations of a target and a nontarget-shape distractor. The attentional account predicts that a line is perceived to grow from the target location to the distractor location because the target location is attended more than the distractor location. In contrast, the binding account predicts the distractor induces as strong illusory motion as the target because a line can be bound with either item (or both items). Subjects reported first the direction of perceived line-growing motion and then the shape of the target using a mouse. Both responses were made in two alternative forced choice.
Figure 2. Results in Experiment 1. T; target, D1; target-shape distractor, D2; nontarget-shape distractor, B; blank. To calculate illusion indices, responses were first coded (e.g., in the T-D1 condition, illusory motion toward D1 was coded 1 whereas illusory motion toward T was coded -1) and averaged. In this way, inconsistent motion direction or no illusion produced an index near zero. Consequently, the direction of line motion was almost random when a line was presented between any two search items but toward a blank location consistently when a line was presented between a search item and a blank location.

Reference

Downing, P. E., & Treisman, A.M. (1997). The line motion illusion: Attention or Impletion? Journal of Experimental Psychology: Human Perception and Performance, 23, 768-779.

Hikosaka, O., Miyauchi, S., & Shimojo, S. (1993). Focal visual attention produces illusory temporal order and motion sensation. Vision Research, 33, 1219-1240.

Kim, M.-S., & Cave, K. R.(1995). Spatial attention in visual search for features and feature conjunctions. Psychological Science, 6, 376-380.

Treisman, A. (1988). Features and objects: the Fourteenth Bartlett Memorial Lecture. The Quarterly Journal of Experimental Psychology, 40A, 201-237.

Yantis, S., & Jonides, J. (1984). Abrupt visual onsets and selective attention: Evidence from visual search, Journal of Experimental Psychology: Human Perception & Performance, 10, 601-621.