Can reptiles perceive visual illusions? Delboeuf illusion in red-footed tortoise (Chelonoidis carbonaria) and bearded dragon (Pogona vitticeps)

Optical illusions have been widely used to compare visual perception among vertebrates because they can reveal how the system is able to adapt to visual input. Sensitivity to visual illusions has never been studied in reptiles. Here, we investigated whether red-footed tortoises, Chelonoidis carbonaria, and bearded dragons, Pogona vitticeps, perceive the Delboeuf illusion. This illusion involves the misperception of the size of a target circle depending upon the context in which it is presented. We adopted the same size discrimination for both species to compare their performance. Animals were presented with two different types of trials. In control trials, they received two different-sized food portions on two plates of the same size. In test trials, they received two same-sized food portions but presented on two different-sized plates. If they perceived the illusion in the same way as humans, we expected them to select the food portion presented on the smaller plate. The tortoises exhibited poor performance in the control trials, which prevented us from drawing any conclusions about their perception of the Delboeuf illusion. In contrast, the bearded dragons selected the larger amount of food in control trials. In test trials, they selected the portion presented on the smaller plate significantly more often than chance, suggesting a human-like sensitivity to the Delboeuf illusion. Our study provides the first evidence of the perception of a visual illusion in a reptile species, suggesting that rather than simply detecting visual input, they interpret sensory information captured by photoreceptors

Do Dogs (Canis lupus familiaris) Make Counterproductive Choices Because They Are Sensitive to Human Ostensive Cues?

Dogs appear to be sensitive to human ostensive communicative cues in a variety of situations, however there is still a measure of controversy as to the way in which these cues influence human-dog interactions. There is evidence for instance that dogs can be led into making evaluation errors in a quantity discrimination task, for example losing their preference for a larger food quantity if a human shows a preference for a smaller one, yet there is, so far, no explanation for this phenomenon. Using a modified version of this task, in the current study we investigated whether non-social, social or communicative cues (alone or in combination) cause dogs to go against their preference for the larger food quantity. Results show that dogs' evaluation errors are indeed caused by a social bias, but, somewhat contrary to previous studies, they highlight the potent effect of stimulus enhancement (handling the target) in influencing the dogs' response. A mild influence on the dog's behaviour was found only when different ostensive cues (and no handling of the target) were used in combination, suggesting their cumulative effect. The discussion addresses possible motives for discrepancies with previous studies suggesting that both the intentionality and the directionality of the action may be important in causing dogs' social biases

Application of an abstract concept across magnitude dimensions by fish

Mastering relational concepts and applying them to different contexts presupposes abstraction capacities and implies a high level of cognitive sophistication. One way to investigate extrapolative abilities is to assess cross-dimensional application of an abstract relational magnitude rule to new domains. Here we show that angelfish initially trained to choose either the shorter of two lines in a spatial task (line-length discrimination task) or the array with “fewer” items (numerical discrimination task) spontaneously transferred the learnt rule to novel stimuli belonging to the previously unseen dimension demonstrating knowledge of the abstract concept of “smaller”. Our finding challenges the idea that the ability to master abstract magnitude concepts across domains is unique to humans and suggests that the circuits involved in rule learning and magnitude processing might be evolutionary conserved

Anisotropy of perceived numerosity: Evidence for a horizontal\u2013vertical numerosity illusion

Many studies have investigated whether numerical and spatial abilities share similar cognitive systems. A novel approach to this issue consists of investigating whether the same perceptual biases underlying size illusions can be identified in numerical estimation tasks. In this study, we required adult participants to estimate the number of white dots in arrays made of white and black dots displayed in such a way as to generate horizontal\u2013vertical illusions with inverted T and L configurations. In agreement with previous literature, we found that participants tended to underestimate the target numbers. However, in the presence of the illusory patterns, participants were less inclined to underestimate the number of vertically aligned white dots. This reflects the perceptual biases underlying horizontal\u2013vertical illusions. In addition, we identified an enhanced illusory effect when participants observed vertically aligned white dots in the T shape compared to the L shape, a result that resembles the length bisection bias reported in the spatial domain. Overall, we found the first evidence that numerical estimation differs as a function of the vertical or horizontal displacement of the stimuli. In addition, the involvement of the same perceptual biases observed in spatial tasks supports the idea that spatial and numerical abilities share similar cognitive processes

Food quantity discrimination in puppies (Canis lupus familiaris)

There is considerable evidence that animals are able to discriminate between quantities. Despite the fact that quantitative skills have been extensively studied in adult individuals, research on their development in early life is restricted to a limited number of species. We, therefore, investigated whether 2-month-old puppies could spontaneously discriminate between different quantities of food items. We used a simultaneous two-choice task in which puppies were presented with three numerical combinations of pieces of food (1 vs. 8, 1 vs. 6 and 1 vs. 4), and they were allowed to select only one option. The subjects chose the larger of the two quantities in the 1 vs. 8 and the 1 vs. 6 combinations but not in the 1 vs. 4 combination. Furthermore, the last quantity the puppies looked at before making their choice and the time spent looking at the larger/smaller amounts of food were predictive of the choices they made. Since adult dogs are capable of discriminating between more difficult numerical contrasts when tested with similar tasks, our findings suggest that the capacity to discriminate between quantities is already present at an early age, but that it is limited to very easy discriminations

Searching for the Critical p of Macphail’s Null Hypothesis: The Contribution of Numerical Abilities of Fish

In 1985, Macphail argued that there are no differences among the intellects of non-human vertebrates and that humans display unique cognitive skills because of language. Mathematical abilities represent one of the most sophisticated cognitive skills. While it is unquestionable that humans exhibit impressive mathematical skills associated with language, a large body of experimental evidence suggests that Macphail hypothesis must be refined in this field. In particular, the evidence that also small-brained organisms, such as fish, are capable of processing numerical information challenges the idea that humans display unique cognitive skills. Like humans, fish may take advantage of using continuous quantities (such as the area occupied by the objects) as proxy of number to select the larger/smaller group. Fish and humans also showed interesting similarities in the strategy adopted to learn a numerical rule. Collective intelligence in numerical estimation has been also observed in humans and guppies. However, numerical acuity in humans is considerably higher than that reported in any fish species investigated, suggesting that quantitative but not qualitative differences do exist between humans and fish. Lastly, while it is clear that contextual factors play an important role in the performance of numerical tasks, inter-species variability can be found also when different fish species were tested in comparable conditions, a fact that does not align with the null hypothesis of vertebrate intelligence. Taken together, we believe that the recent evidence of numerical abilities in fish call for a deeper reflection of Macphail’s hypothesis

Anisotropy of perceived space in non-primates? The horizontal-vertical illusion in bearded dragons (Pogona vitticeps) and red-footed tortoises (Chelonoidis carbonaria)

The horizontal-vertical illusion is a size illusion in which two same-sized objects appear to be different if presented on a horizontal or vertical plane, with the vertical one appearing longer. This illusion represents one of the main evidences of the anisotropy of the perceived space of humans, an asymmetrical perception of the object size presented in the vertical and horizontal space. Although this illusion has been widely investigated in humans, there is an almost complete lack of studies in non-human animals. Here we investigated whether reptiles perceive the horizontal-vertical illusion. We tested two reptile species: bearded dragons (Pogona vitticeps) and red-footed tortoises (Chelonoidis carbonaria). In control trials, two different-sized food strips were presented and animals were expected to choose the longer one. In test trials, animals received two same-sized strips, presented in a spatial arrangement eliciting the illusion. Only bearded dragons significantly preferred the longer strip in control trials; in test trials, bearded dragons selected the strip arranged vertically, suggesting a human-like perception of this pattern, while no clear choice for either array was observed in tortoises. Our results raise the interesting possibility that the anisotropy of perceived space can exists also in a reptile brain

Are cerebral and behavioural lateralization related to anxiety-like traits in the animal model zebrafish (Danio rerio)?

Brain lateralization refers to hemispheric asymmetries in functions and/or neuroanatomical structures. Functional specialization in non-human animals has been mainly inferred through observation of lateralized motor responses and sensory perception. Only in a few cases has the influence of brain asymmetries on behaviour been described. Zebrafish has rapidly become a valuable model to investigate this issue as it displays epithalamic asymmetries that have been correlated to some lateralized behaviours. Here we investigated the relation between neuroanatomical or behavioural lateralization and anxiety using a light-dark preference test in adult zebrafish. In Experiment 1, we observed how scototaxis response varied as a function of behavioural lateralization measured in the detour task as turning preference in front of a dummy predator. In Experiment 2, foxD3:GFP transgenic adult zebrafish with left or right parapineal position, were tested in the same light-dark test as fish in Experiment 1. No correlation was found between the behaviour observed in the detour test and in the scototaxis test nor between the left- and right-parapineal fish and the scototaxis response. The consistency of results obtained in both experiments indicates that neither behavioural nor neuroanatomical asymmetries are related to anxiety-related behaviours measured in the light-dark test

Learning by doing: The use of distance, corners and length in rewarded geometric tasks by Zebrafish (Danio Rerio)

Zebrafish spontaneously use distance and directional relationships among three-dimensional extended surfaces to reorient within a rectangular arena. However, they fail to take advantage of either an array of freestanding corners or an array of unequal-length surfaces to search for a no-longer-present goal under a spontaneous cued memory procedure, being unable to use the information supplied by corners and length without some kind of rewarded training. The present study aimed to tease apart the geometric components characterizing a rectangular enclosure under a procedure recruiting the reference memory, thus training zebrafish in fragmented layouts that provided differences in surface distance, corners, and length. Results showed that fish, besides the distance, easily learned to use both corners and length if subjected to a rewarded exit task over time, suggesting that they can represent all the geometrically informative parts of a rectangular arena when consistently exposed to them. Altogether, these findings highlight crucially important issues apropos the employment of different behavioral protocols (spontaneous choice versus training over time) to assess spatial abilities of zebrafish, further paving the way to deepen the role of visual and nonvisual encodings of isolated geometric components in relation to macrostructural boundaries