The effect of light-incubation on ordinal processing: a study on day-old domestic chick (Gallus gallus)

Numerical cognition has been studied in a wide range of animals and its presence has been observed in an increasing number of species with distant phylogenetic roots, including mammals, birds, reptiles, amphibians, and insects. Research has discovered a space-number association (SNA) connecting number processing and perceptive visual system. As with the human mental number line, a leftward bias for low quantity was discovered in various species. Newborn domestic chicks (Gallus gallus) performing magnitude and ordinal tasks provided valuable data into the possible mechanisms underlying SNA and leftward bias. Their visual system serves as an excellent model for studying the association among space and number. The almost complete absence of interhemispheric decussation provides an opportunity to investigate the effects of lateralization in cognition and behaviour, while monocular tasks can assess one hemisphere at a time. Nevertheless, hemispheric lateralization can be manipulated during a sensitive period of incubation through exposure to light, resulting in strongly lateralized chicks. Based on previous work on strongly vs. weakly lateralized chicks performing ordinal task, the current research investigates how light incubation influences only numerical processing. Fifty-two male domestic chicks were used: 26 strongly lateralized and 26 weakly lateralized. Both groups followed the same procedures and tasks. In the tests employed, the inter-element distance was not maintained fixed, implying that no spatial information was available for processing.