Distance and magnitude effects in sequential number discrimination by pigeons

Number discrimination experiments with humans and monkeys have revealed distance and magnitude effects. When required to choose the more frequently occurring stimulus between two stimuli presented repeatedly in sequence, accuracy improves as the distance between number increases (distance effect) and decreases as distance is held constant and the size of the numbers increases (magnitude effect). These effects were shown in three experiments reported with pigeons as subjects. It was shown that a single model based on discrimination between noisy numerical representations could account for both the primate and bird findings. To model the pigeon data, an additional decay parameter was necessary to account for strong recency effects found for the influence on choice of terminal stimuli presented in a sequence.