Changes in Pigeons’ Responses to Numerical Stimuli Depending on Total Element Area Differences between Stimuli

Abstract

This experiment investigated whether pigeons’ response to numerical stimuli in a numerosity discrimination task differed by degree of difference in total element area ratio between numerical stimuli. After the pigeons learned to respond to a smaller numerical stimulus containing fewer elements, Tests 1 and 2 were conducted. In Test 1, the study compared smaller numerical stimulus choice ratios under several conditions, wherein the ratios of the total element area between smaller and larger numerical stimuli were manipulated. Test 2 presented a test pair with the same number of pairs, but whose areas differed, and examined whether discrimination based on total element area was established through different reinforcements within the numerosity discrimination task. In Test 1, birds responded to smaller numerical stimuli under the conditions that the total area of the smaller numerical stimuli was less than or equal to that of the larger numerical stimuli. On the other hand, under the condition that the total area of the smaller numerical stimuli was larger than that of the larger numerical stimuli, the frequency of responses to the smaller numerical stimuli decreased with the increase in differences in the area ratio between stimuli. Test 2 demonstrated that the birds consistently chose the smaller area of stimuli when the numerical stimulus pairs differed only in area size. These results suggested that either stimulus control by numerosity or by nonnumerical visual cues is dominant, depending on the degree of the total element area ratio between the numerical stimuli.