Fun Bird Fact
This entry was posted on 5/1/2008 7:45 AM and is filed under perception.
In Perception ...
Processing of the Müller-Lyer illusion by a Grey parrot (Psittacus erithacus)
Irene M Pepperberg, Jennifer Vicinay, Patrick Cavanagh
Received 28 November 2006, in revised form 31 May 2007; published online 1 May 2008
Abstract. Alex, a Grey parrot (Psittacus erithacus)
who identifies the bigger or smaller of two objects by reporting its
color or matter using a vocal English label and who states “none” if
they do not differ in size, was presented with two-dimensional
Müller-Lyer figures (Brentano form) in which the central lines were of
contrasting colors. His responses to “What color bigger/smaller?''
demonstrated that he saw the standard length illusion in the
Müller-Lyer figures in 32 of 50 tests where human observers would also
see the illusion and reported the reverse direction only twice. He did
not report the illusion when (a) arrows on the shafts were
perpendicular to the shafts or closely approached perpendicularity,
(b) shafts were 6 times thicker than the arrows, or (c) after being
tested with multiple exposures—conditions that also lessen or eliminate
the illusion for human observers. These data suggest that parrot and
human visual systems process the Müller-Lyer figure in analogous ways
despite a 175-fold difference in the respective sizes of their brain
volumes. The similarity in results also indicates that parrots with
vocal abilities like Alex’s can be reliably tested on visual illusions
with paradigms similar to those used on human subjects.
