Spontaneous quantity discrimination in the auditory domain in naïve domestic chicks

Numerical abilities are widespread across the animal kingdom and are not exclusive to humans. Several animal species, including domestic chickens (Gallus gallus), have demonstrated the capacity to discriminate numerosities. Importantly, some of these abilities emerge spontaneously already in newly-hatched chicks, without the need for explicit training. However, research to date has focused exclusively on the visual modality, leaving open the question of whether chicks can discriminate numerosities in the auditory domain, despite evidence that they can discriminate other auditory features such as tone and rhythm. Here, we investigated, for the first time, spontaneous numerical discrimination in the auditory modality in naïve domestic chicks. In Experiment 1, we tested newly-hatched chicks’ spontaneous ability to discriminate between two auditory sequences differing in the number of composing elements (4 vs. 12 identical sounds), without controlling for other physical properties. In Experiment 2, we controlled for the total duration and overall amount of sound across sequences. Our results revealed a preference for the 12-sound sequence only when duration and sound amount were not matched between the stimuli. When these properties were controlled, no preference was observed. These findings suggest that while chicks are sensitive to overall magnitude in the auditory domain (e.g., longer duration or greater amount of sound), they do not spontaneously discriminate numerical differences in sound sequences when other continuous variables are held constant. Future studies will investigate the role of specific stimulus features in determining this preference. For example, they will examine whether and how the results change when a heterogeneous set of stimuli is presented.