Abstract
Illusory Line Motion (i.e., a static line, presented after a lateral cue, is perceived as movement in the opposite direction to the cue) has been used to study a phenomenon of perceptual asymmetry. We have demonstrated the presence of an illusion of leftward movement, even in the presence of bilateral symmetrical cues. We have classified this phenomenon as one of pseudo-extinction. The paradigm of the four experiments performed was always the same: a white line, briefly presented alone or preceded by one or two lateral cues (150 ms), was judged by a group of young participants to be moving either to one side or the other. The asymmetrical effect in the bilateral cue condition was observed with horizontal lines (Experiment 1 and 4), and not with vertical or oblique (Experiment 2 and 3). These results suggest that the effect is linked to the asymmetry of the horizontal spatial planum and the mechanisms of spatial attention. Experiment 4 verified whether the Illusory Line Motion involves the collicular pathway by using blue stimuli for the cues, which activate less the Superior Colliculus (SC), with negative results. We interpreted the asymmetrical pseudo-extinction phenomenon in terms of a right-space exogenous attention advantage.
Highlights
In illusory line motion (ILM), a dot is presented, followed by, after a short delay, a line or bar, abutting the spot at one of its ends
In order to test whether an illusory effect was present under unilateral and under asbilateral the dependent variable and the Cue Condition as a repeated
The results of the actual experiment confirm the presence of the illusory effect in the unilateral conditions, not the asymmetrical effect of the bilateral cue conditions
Summary
In illusory line motion (ILM), a dot is presented, followed by, after a short delay, a line or bar, abutting the spot at one of its ends. The effect was firstly described by Kanizsa [1], Kanizsa and Legrenzi [4] (who named it polarized gamma motion, PGM) and re-discovered by Hikosaka, Miyauchi and Shimojo [2,3], who attributed it to an attentional gradient such that regions of the line closest to the attended spot are processed faster, and thereby activate higher-level motion detectors sooner This sensory account has been questioned in subsequent studies, favoring instead an account in which the illusion is the result of an impletion process that fills in interpolated events after the cue and the line are linked as successive states of a single object in apparent motion [5]. This latter explanation for ILM emphasizes higher-level processes that ensure object continuity and coherence, rather than the firing of motion detectors resulting from
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