Re-evaluating birds' ability to detect Glass patterns

Glass patterns (GPs) are static stimuli that consist of randomly positioned dot-pairs that are spatially integrated to create the perception of a global form. However, when multiple independently generated static GPs are presented sequentially (termed 'dynamic' GP), observers report a percept of coherent motion, and data show an improvement in sensitivity. This increased sensitivity has been attributed to a summation of the form signals provided by the individual GPs. In Experiment 1, we tested whether pigeons also show a heightened sensitivity to dynamic GPs. Our results show that pigeons are significantly better at learning to discriminate dynamic GPs from noise compared with static GPs. However, in contrast to previous research, we found that pigeons did not perform well enough with our static GPs to extract sensitivity measurements. In Experiment 2, we compared our static GPs to those that have been used previously. We show that the difference in the comparison noise patterns is important. We used dipole noise patterns, while previous studies used uniform noise patterns that differ in mean dot spacing to the S+. We argue that prior findings from the use of GPs in pigeons should be re-evaluated using dynamic GP stimuli with noise that consist of dipoles.