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Cynthia M. Henderson, James L. McClelland; Common Spatial Characteristics of Illusory Conjunctions and Crowding. Journal of Vision 2012;12(9):340. doi: 10.1167/12.9.340.
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An illusory conjunction (IC) can be defined as a perceptual error in which a subject reports a stimulus that did not appear but that combines features of the stimuli that were present. Pelli, Palomares, & Majaj (2004) noted that many IC studies use stimuli whose target-flanker proximity falls within the critical spacing for crowding. For example, Prinzmetal, Henderson, & Ivry (1995) found ICs using stimuli separated by less than 15% of the target’s eccentricity. On the other hand, Cohen & Ivry (1989) found ICs with stimuli whose spacing far exceeded typical crowding values, although they used a dual task procedure with an extra memory load.
To test the importance of crowding-like proximity for ICs, we replicated Prinzmetal et al (Experiment 2, no-RSVP condition) and compared ICs when stimulus spacing was or was not within typical crowding values. We found ICs with small stimulus spacing but no evidence for ICs when the spacing was increased.
Our second experiment replicated Cohen & Ivry (Experiment 3) and found ICs between distant stimuli. Following their procedure, subjects identified non-target stimuli before responding about the target. Our third experiment used the same stimuli as our second experiment, but the non-target identification task was removed. Stimulus durations and contrast were also reduced such that accuracy did not differ significantly between the second and third experiments. Without a dual task procedure, the number of illusory conjunctions was significantly less than would be expected by chance, suggesting that the ICs found by Cohen & Ivry may be related to issues of memory load and response selection.
We have replicated previous IC results in finding a reduction in ICs when stimulus spacing was increased. Furthermore, our results suggest that the same spacing constraints critical for crowding might play a role in illusory conjunctions.
Meeting abstract presented at VSS 2012
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