Review of studies on visual perception in grey parrots (Psittacus erithacus): The Müller-Lyer illusion, amodal and modal completion

I.M Pepperberg

doi:10.26451/abc.04.03.14.2017

Abstract

Review of studies on visual perception in grey parrots (Psittacus erithacus): The Müller-Lyer illusion, amodal and modal completion

Highlights

To better understand the evolution and architecture of visual cognition and visual attention in humans, researchers often study visual processing in other species
Comparative behavioral research—how subjects respond to stimuli—efficiently answers basic questions about how different cognitive architectures process equivalent information: Resultant cross-species comparisons permit identification of both critical, core elements that are preserved across divergent cognitive architectures and those that may be unique to humans (e.g., Feng, Chouinard, Howell, & Bennett, 2016; Jackson & Cormack, 2007)
Alex’s responses varied not with overall length of the stimuli but rather with the ratio of shaft/arrow width as well as shaft/arrow angle, suggesting how emphasis on certain local cues can affect responses. Had he responded solely to the total length of the stimuli, he would not have failed to see the illusion in stimuli where the shafts were six times wider than the 45o arrows and would have seen the illusion more often than he did for stimuli in which the arrows and shafts were wide (4mm for both, 45o arrows). These findings are, consistent with attention being focused on certain local cues, as the 6-mm shafts tend to draw attention strongly away from the effects of the arrows, at least until the arrows themselves were extreme (e.g., 10o) and acted to reinstate a response to the illusion— less strongly than in the original form tested (4-mm shafts, 1 mm and 45o arrows)

Summary

Introduction

To better understand the evolution and architecture of visual cognition and visual attention in humans, researchers often study visual processing in other species. Parrots’ perceptual traits are likely to have been selected by evolutionary pressures somewhat similar to those of early primates (see Demery, Chappell, & Martin, 2011): Field studies (May, 2004) reveal that Grey parrots forage over large distances (60 km/day) in multiple habitats (e.g., juicing bark and eating fruit in forest trees, consuming herbs and soil at ground-level savannes); need to be alert for aerial and terrestrial predators; and split their time among large flocks, small groups, and isolated pairs All these activities involve visual processing and a great need for visual accuracy. Psittacine UV color perception, is likely more closely related to that of the pigeon than to the chick (Carvalho, Knott, Berg, Bennett, & Hunt, 2011) With this information in mind, my colleagues and I decided to examine how Grey parrots, who could respond vocally as do humans, would process a variety of optical illusions. The data would provide information on how Grey parrots literally see their world

Methods

Results

Conclusion