Fish are Sensitive to Expansion-Contraction Color Effects

Abstract

Citation -Albertazzi, L., Rosa-Salva, O., Da Pos, O., Sovrano, V. A. (2015). Fish are sensitive to expansioncontraction color effects. Animal Behavior and Cognition, 4(3), 349-364. https://doi.org/10.26451/abc.04.03.12.2017Abstract -Some visual phenomena reveal the visual system's tendency to structure the scene according to rules that do not always have a direct correspondence in the external physical world. Color information can affect the perception of other object attributes such as size, generating contextual expansion, and contraction effects. We investigated phenomena of this kind in redtail splitfin fish (Xenotoca eiseni, family Goodeidae). As in previous studies, the fish were trained to discriminate a larger from a smaller grey rectangle in order to locate the exit from the test tank. The fish were then presented with two rectangles of equal size but different colors. Isoluminant colors were employed for each pair to control for luminance contrast from the background. The fish were tested in three different conditions with three color pairs corresponding to the human yellow-blue, red-green, and red-blue. The three color test conditions affected fish responses in significantly different ways. In the blue-yellow condition the fish seemed to experience the expansion-contraction effects as reported by human observers. By contrast, no difference between the choices of the two training groups was observed in the red-green and red-blue conditions. This is the first demonstration of human-like phenomenal chromatic expansion-contraction effects in non-human animals. Notably, the effect of the yellow-blue pair, which is usually the one most pronounced in humans, seems to be robust also under conditions of isoluminance in our model species. Future studies could repeat the experiment using non-isoluminant pairs that better preserve the connotative chromatic dimensions in humans.

“Classifying-together” phenomenon in fish (Xenotoca eiseni): Simultaneous exposure to visual stimuli impairs subsequent discrimination learning

“…42 X. eiseni took part in Experiment 1 (Visual discrimination learning between a full red disk and an amputated red disk), 42 fish took part in Experiment 2 (Visual discrimination learning between a full red disk and a red cross), and 28 fish took part in Experiment 3. Because of high motivation to rejoin female conspecifics, only males were engaged in these experiments (following the same procedure reported in previous studies [18][19][20][21][22][23][24][25]).…”

“…After the exposure, fish performed the visual discrimination learning ("training-phase"). The experimental apparatus was the same used in previous studies investigating visual discrimination in X. eiseni [16][17][18][19][20][21], and it consisted of a white plastic (Poliplak 1 ) octagonal arena (oblique segment: 4 x 15 cm; straight segment 9 x 15 cm) inscribed in a squared one (15 x 15 x 15 cm); see Fig 2A . The arena was then placed in a larger rectangular tank (57 x 18 x 38 cm) to get a surrounding comfortable region with plants, food, and two female conspecifics (not engaged in the behavioral observations), hence providing an incentive to go out of the arena for the experimental subjects [18][19][20][21][22][23][24][25]. Fish could leave the innermost zone of the apparatus by crossing two rectangular corridors (3 x 4.5 cm, 2.5 cm in length, 2.5 cm from the floor, see Fig 2B) located at the two diagonally opposite corners of the arena.…”

“…The training-phase consisted of daily sessions of 10 trials until the learning criterion, that is, at least 70% (or more) of correct choices per two consecutive daily sessions (binomial test for first choices p<0.03; binomial test for total choices p<0.001). This criterion is common to other similar discriminative learning experiments [18][19][20][21][22][23][24][25], and it is intended to maintain procedural continuity and to have the opportunity to perform behavioral comparisons. Before starting each experimental trial, the fish was brought from the comfortable zone surrounding the arena and gently transferred into a transparent glass cylinder (diameter: 6 cm, height: 8 cm, open at both ends), thus placed into the center of the arena.…”

“…The sample size in each experimental condition (N = 7) was similar to the one used in studies employing the same kind of tasks available in literature among fish species (for an example see [18][19][20][21][22][23][24][25]). Moreover, the number of animals observed was consistent with the ethical method of "Reduction", which allows considering the minimum number of animals to draw statistically valid results.…”

“…Given the supposed inconsistency of the behavioral data collected in a small number of vertebrates (chicks, monkeys, rats), the present study aimed to investigate the classifying-together effect in redtail splitfin fish (Xenotoca eiseni), that is, a teleost widely employed in manifold studies on animal cognition (social laterality: [7,8]; spatial abilities: [9][10][11][12][13][14][15][16]; detour behavior: [17]; visual discrimination learning and optical illusions: [18][19][20][21][22][23]; numerical abilities: [24]), thus also extending the investigation to a class of vertebrates phylogenetically remote from birds and mammals. To this end, we performed two discrimination learning experiments after rearing different groups of fish with pairs of two-dimensional visual stimuli for 50 consecutive days.…”