• squirrel monkeys;
  • neon-color spreading;
  • visual illusion


In three experiments, we explored the perception of neon-color spreading in squirrel monkeys and compared it with that of humans. In Experiment 1, human observers were tested to confirm the effect of stimulus aspects that were controlled in a series of experiments on the neon-color effect. The strength of the neon-color effect was modulated by the width, spacing, and luminance ratio of crosshatched lines that induced neon-color spreading. In Experiment 2A, one squirrel monkey was taught to discriminate a circle from three other shapes induced by the neon-color effect under the same stimulus conditions as in Experiment 1. The dependent measure was the percentage of correct responses. In Experiment 2B, two monkeys were trained to discriminate a target stimulus from three nontarget stimuli that were neon-color effect versions of the target stimulus. The dependent measure was the error rate that monkeys committed in their task of discrimination. The results in Experiments 2A and 2B were comparable with the results in Experiment 1, which suggests that squirrel monkeys perceive neon-color spreading.