Journal
CANADIAN JOURNAL OF EXPERIMENTAL PSYCHOLOGY-REVUE CANADIENNE DE PSYCHOLOGIE EXPERIMENTALE
Volume 74, Issue 3, Pages 201-206Publisher
CANADIAN PSYCHOLOGICAL ASSOC
DOI: 10.1037/cep0000203
Keywords
reptile cognition; visual illusions; size illusions; Delboeuf illusion; red-footed tortoises
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Funding
- STARS@unipd (ANIM_ILLUS) grant from the University of Padova
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Visual illusions have been widely used as a tool to study animal visual perception. In many cases, identical experimental procedures were adopted to make highly controlled interspecific comparisons. However, reducing methodological variability may prevent reliable comparisons because a certain methodology could be more suitable for some species than others. This study sought to build on previous work that investigated the perception of the Delboeuf illusion in reptiles. Reptiles were presented with trials composed of 2 different-sized food portions on 2 identical plates in which they were expected to maximize their food intake. In contrast to the bearded dragons (Pogona vitticeps), tortoises (Chelonoidis carbonaria) performed poorly in all conditions and therefore no firm conclusion regarding their perception of the illusion could be made. Such results could be due to cognitive challenges or due to the experimental setup. because descending a ramp is demanding for the tortoises. In this study. we adopted the same experimental paradigm but in a flat apparatus. Tortoises significantly discriminated the larger food portions in baseline trials, however, their performance did not differ from chance in illusory trials revealing that, under these conditions, they are not sensitive to the Delboeuf illusion. This nonperception could be ascribed to different factors, such as poorer discrimination ability or a low sensitivity to contrast and assimilation phenomena. Our study highlights the importance of additional investigation to better understand the nature of null results, taking in consideration the ecological needs of the species before drawing any conclusions about its abilities.
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