Numerical auditory processing and cross-modal matching in domestic chicks

Domestic chicks’ visual numerical representations have been extensively studied, but their capacity to process acoustical numerical information and to match it between acoustic and visual modalities is much less investigated. Here we target these questions, studying filial imprinting and spontaneous preferences for visual and/or auditory stimuli of different numerosity. For imprinting studies, chicks hatching in darkness were exposed to a sequence composed of a single note repeated either four or twelve times. During the subsequent test, chicks had to choose between the familiar imprinting stimulus (e.g., twelve notes) and the other numerosity (e.g., four notes). In a set of companion experiments, naïve chicks were used to study inborn preferences between auditory sequences composed of different numbers of notes. Overall, this line of research revealed spontaneous preferences for the larger set of acoustical elements, rather than for the familiar numerosity, in line with what is often found in the visual modality (e.g., Rugani et al., 2010). This preference, however, appeared to depend on the availability of information provided by continuous variables that correlate with the numerosity. This pattern was also confirmed by cross-modal transfer tests, during which after acoustical imprinting chicks could choose between visual stimuli of different numerosity.