title: The Müller-Lyer illusion in the teleost fish Xenotoca eiseni.
abstract: In the Müller-Lyer illusion, human subjects usually see a line with two inducers at its ends facing outwards as longer than an identical line with inducers at its ends facing inwards. We investigate the tendency for fish to perceive, in suitable conditions, line length according to the Müller-Lyer illusion. Redtail splitfins (Xenotoca eiseni, family Goodeidae) were trained to discriminate between two lines of different length. After reaching the learning criterion, the fish performed test trials, in which they faced two lines (black or red) of identical length, differing only in the context in terms of arrangement of the inducers, which were positioned at the ends of the line, either inward, outward, or perpendicular. Fish chose the stimulus that appear to humans as either longer or shorter, in accordance with the prediction of the Müller-Lyer illusion, consistently with the condition of the training. These results show that redtail splitfins tend to be subject to this particular illusion. The results of the study are discussed with reference to similar studies concerning the same illusion as recently observed in fish. Contrasting results are presented. The significance of the results in light of their possible evolutionary implications is also discussed.
authors.affiliation: Center for Mind/Brain Sciences (CIMeC), University of Trento, P.zza Manifattura 1 and C.so Bettini 31, 38068, Rovereto, Trento, Italy. valeriaanna.sovrano@unitn.it.|Department of Psychology and Cognitive Sciences, University of Trento, C.so Bettini 31, 38068, Rovereto, Trento, Italy. valeriaanna.sovrano@unitn.it.
authors.forename: Valeria Anna
authors.initials: VA
authors.lastname: Sovrano
authors.affiliation: Department of General Psychology, University of Padua, Via Venezia 8, 35131, Padua, Italy. osvaldo.dapos@gmail.com.
authors.forename: Osvaldo
authors.initials: O
authors.lastname: da Pos
authors.affiliation: Center for Mind/Brain Sciences (CIMeC), University of Trento, P.zza Manifattura 1 and C.so Bettini 31, 38068, Rovereto, Trento, Italy. liliana.albertazzi@unitn.it.|Department of Humanities, University of Trento, Via Tommaso Gar 14, 38122, Trento, Italy. liliana.albertazzi@unitn.it.
authors.forename: Liliana
authors.initials: L
authors.lastname: Albertazzi
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D003532:Cyprinodontiformes / Q000502:physiology*; D004192:Discrimination, Psychological; D005260:Female; D008297:Male; D009903:Optical Illusions; D010775:Photic Stimulation; D012858:Size Perception
keywords: Fish; Global versus local factors; Illusions; Visual perception