1979 volume 8(2) pages 187 – 197

Cite as:
Brigell M, Uhlarik J, 1979, "The relational determination of length illusions and length aftereffects" Perception 8(2) 187 – 197

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The relational determination of length illusions and length aftereffects

Mitchell Brigell, John Uhlarik

Received 18 July 1978, in revised form 12 March 1979

Abstract. When two lines were presented simultaneously, in an illusion paradigm, the judged length of one of the lines (the focal line) assimilated toward the length of the contextual line. When the lines were presented sequentially, in an aftereffect paradigm, the apparent length of the focal line was displaced away from the length of a previously presented contextual line (i.e. contrast). The largest effects obtained at inverse contextual-to-focal length ratios: 1.67 : 1 for contextual lines longer than the focal line and 0.60 : 1 for contextual lines shorter than the focal line. Overestimation of focal length was larger than underestimation for both illusions and aftereffects despite the fact lhat identical stimuli produced effects in opposite directions in the two paradigms. Results were discussed in terms of a neural length-coding model and were related to visual size constancy.

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