title: At first glance, transparency enhances assimilation.
abstract: We investigated the role of transparency, perceptual grouping, and presentation time on perceived lightness. Both transparency and perceptual grouping have been found to result in assimilation effects, but only for ambiguous stimulus displays and with specific attentional instructions. By varying the presentation times of displays with two partly overlapping transparent E-shaped objects, we measured assimilation in unambiguous stimulus displays and without specific attentional instructions. The task was to judge which of two simultaneously presented E-shaped objects was darker. With unrestrained presentation times, if a transparency interpretation was possible, assimilation was not found. Inhibiting a transparency interpretation by occluding the local junctions between the two E-shaped objects, did lead to assimilation. With short presentation times, if a transparency interpretation was possible, assimilation was now also found. Thus, we conclude that, although transparency appears to enhance assimilation, with unambiguous stimulus displays and without specific attentional instructions, perceptual grouping is more important for assimilation to occur.
authors.affiliation: Nijmegen Institute for Cognition and Information, Radboud University Nijmegen, PO Box 9104, 6500 HE Nijmegen, The Netherlands. a.koning@nici.ru.nl
authors.forename: Arno
authors.initials: A
authors.lastname: Koning
authors.forename: Charles M M
authors.initials: CM
authors.lastname: de Weert
authors.forename: Rob
authors.initials: R
authors.lastname: van Lier
mesh_terms: D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D006801:Humans; D008029:Lighting; D009903:Optical Illusions; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010470:Perceptual Masking; D011601:Psychophysics; D013997:Time Factors