One, two, three, four, or is there something more? Numerical discrimination in day-old domestic chicks

Human adults master sophisticated, abstract numerical calculations that are mostly based on symbolic language and thus inimitably human. Humans may nonetheless share a subset of non-verbal numerical skills, available soon after birth and considered the evolutionary foundation of more complex numerical reasoning, with other animals. These skills are thought to be based on the two systems: the object file system which processes small values (<3) and the analogue magnitude system which processes large magnitudes (>4). Infants’ ability to discriminate 1 vs. 2, 1 vs. 3, 2 vs. 3, but not 1 vs. 4, seems to indicate that the two systems are independent, implying that the conception of a continuous number processing system is based on precursors that appear to be interrupted at or about the number four. The findings from the study being presented here indicating that chicks are able to make a series of discriminations regarding that borderline number (1 vs. 4, 1 vs. 5, 2 vs. 4) support the hypothesis that there is continuity in the number system which processes both small and large numerousness.     

When preschoolers follow their eyes and older children follow their noses: visuo‐olfactory social affective matching in childhood

Recognition of emotional facial expressions is a crucial skill for adaptive behavior that most often occurs in a multi‐sensory context. Affective matching tasks have been used across development to investigate how people integrate facial information with other senses. Given the relative affective strength of olfaction and its relevance in mediating social information since birth, we assessed olfactory–visual matching abilities in a group of 140 children between the ages of 3 and 11 years old. We presented one of three odor primes (rose, fish and no‐odor, rated as pleasant or unpleasant by individual children) before a facial choice task (happy vs. disgusted face). Children were instructed to select one of two faces. As expected, children of all ages tended to choose happy faces. Children younger than 5 years of age were biased towards choosing the happy face, irrespective of the odor smelled. After age 5, an affective matching strategy guided children's choices. Smelling a pleasant odor predicted the choice of happy faces, whereas smelling the unpleasant or fish odor predicted the choice of disgusted faces. The present study fills a gap in the developmental literature on olfactory‐visual affective strategies that affect decision‐making, and represents an important step towards understanding the underlying developmental processes that shape the typical social mind.     

Perception of the Ebbinghaus illusion in four-day-old domestic chicks (Gallus gallus)

In the Ebbinghaus size illusion, a central circle surrounded by small circles (inducers) appears bigger than an identical one surrounded by large inducers. Previous studies have failed to demonstrate sensitivity to this illusion in pigeons and baboons, leading to the conclusion that avian species (possibly also nonhuman primates) might lack the neural substrate necessary to perceive the Ebbinghaus illusion in a human-like fashion. Such a substrate may have been only recently evolved in the primate lineage. Here, we show that this illusion is perceived by 4-day-old domestic chicks. During rearing, chicks learnt, according to an observational-learning paradigm, to find food in proximity either of a big or of a small circle. Subjects were then tested with Ebbinghaus stimuli: two identical circles, one surrounded by larger and the other by smaller inducers. The percentage of approaches to the perceptually bigger target in animals reinforced on the bigger circle (and vice versa for the other group) was computed. Over four experiments, we demonstrated that chicks are reliably affected by the illusory display. Subjects reinforced on the small target choose the configuration with big inducers, in which the central target appears perceptually smaller; the opposite is true for subjects reinforced on the big target. This result has important implications for the evolutionary history of the neural substrate involved in the perception of the Ebbinghaus illusion.