Hdl Handle:
http://hdl.handle.net/10149/97396
Title:
Impossible shadows and lightness constancy
Authors:
Soranzo, A. (Alessandro); Agostini, T. (Tiziano)
Affiliation:
University of Trieste. Department of Psychology.
Citation:
Soranzo, A. and Agostini, T. (2004) 'Impossible shadows and lightness constancy', Perception, 33 (11), pp.1359-1368.
Publisher:
Pion
Journal:
Perception
Issue Date:
2004
URI:
http://hdl.handle.net/10149/97396
DOI:
10.1068/p5282
Abstract:
The intersection between an illumination and a reflectance edge is characterised by the 'ratio-invariant' property, that is the luminance ratio of the regions under different illumination remains the same. In a CRT experiment, we shaped two areas, one surrounding the other, and simulated an illumination edge dividing them in two frames of illumination. The portion of the illumination edge standing on the surrounding area (labelled contextual background) was the contextual edge, while the portion standing on the enclosed area (labelled mediating background) was the mediating edge. On the mediating background, there were two patches, one per illumination frame. Observers were asked to adjust the luminance of the patch in bright illumination to equate the lightness of the other. We compared conditions in which the luminance ratio at the contextual edge could be (i) equal (possible shadow), or (ii) larger (impossible shadow) than that at the mediating edge. In addition, we manipulated the reflectance of the backgrounds. It could be higher for the contextual than for the mediating background; or, vice versa, lower for the contextual than for the mediating background. Results reveal that lightness constancy significantly increases when: (i) the luminance ratio at the contextual edge is larger than that at the mediating edge creating an impossible shadow, and (ii) the reflectance of the contextual background is lower than that of the mediating one. We interpret our results according to the albedo hypothesis, and suggest that the scission process is facilitated when the luminance ratio at the contextual edge is larger than that at the mediating edge and/or the reflectance of the including area is lower than that of the included one. This occurs even if the ratio-invariant property is violated.
Type:
Article
Language:
null
Keywords:
impossible shadows; lightness constancy; luminance ratio; scission process
ISSN:
0301-0066; 1468-4233
Rights:
Subject to restrictions, author can archive post-print (ie final draft post-refereeing). For full details see http://www.sherpa.ac.uk/romeo/ [Accessed 26/04/2010]
Citation Count:
5 [Scopus, 26/04/2010]

Full metadata record

DC FieldValue Language
dc.contributor.authorSoranzo, A. (Alessandro)en
dc.contributor.authorAgostini, T. (Tiziano)en
dc.date.accessioned2010-04-26T13:38:20Z-
dc.date.available2010-04-26T13:38:20Z-
dc.date.issued2004-
dc.identifier.citationPerception; 33 (11): 1359-1368en
dc.identifier.issn0301-0066-
dc.identifier.issn1468-4233-
dc.identifier.doi10.1068/p5282-
dc.identifier.urihttp://hdl.handle.net/10149/97396-
dc.description.abstractThe intersection between an illumination and a reflectance edge is characterised by the 'ratio-invariant' property, that is the luminance ratio of the regions under different illumination remains the same. In a CRT experiment, we shaped two areas, one surrounding the other, and simulated an illumination edge dividing them in two frames of illumination. The portion of the illumination edge standing on the surrounding area (labelled contextual background) was the contextual edge, while the portion standing on the enclosed area (labelled mediating background) was the mediating edge. On the mediating background, there were two patches, one per illumination frame. Observers were asked to adjust the luminance of the patch in bright illumination to equate the lightness of the other. We compared conditions in which the luminance ratio at the contextual edge could be (i) equal (possible shadow), or (ii) larger (impossible shadow) than that at the mediating edge. In addition, we manipulated the reflectance of the backgrounds. It could be higher for the contextual than for the mediating background; or, vice versa, lower for the contextual than for the mediating background. Results reveal that lightness constancy significantly increases when: (i) the luminance ratio at the contextual edge is larger than that at the mediating edge creating an impossible shadow, and (ii) the reflectance of the contextual background is lower than that of the mediating one. We interpret our results according to the albedo hypothesis, and suggest that the scission process is facilitated when the luminance ratio at the contextual edge is larger than that at the mediating edge and/or the reflectance of the including area is lower than that of the included one. This occurs even if the ratio-invariant property is violated.en
dc.language.isonullen
dc.publisherPionen
dc.rightsSubject to restrictions, author can archive post-print (ie final draft post-refereeing). For full details see http://www.sherpa.ac.uk/romeo/ [Accessed 26/04/2010]en
dc.subjectimpossible shadowsen
dc.subjectlightness constancyen
dc.subjectluminance ratioen
dc.subjectscission processen
dc.titleImpossible shadows and lightness constancy-
dc.typeArticleen
dc.contributor.departmentUniversity of Trieste. Department of Psychology.en
dc.identifier.journalPerceptionen
ref.citationcount5 [Scopus, 26/04/2010]en
or.citation.harvardSoranzo, A. and Agostini, T. (2004) 'Impossible shadows and lightness constancy', Perception, 33 (11), pp.1359-1368.-
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