Date of Award

Fall 11-25-2019

Document Type


Degree Name

Master of Arts (MA)



First Advisor

Dr. Sarah-Elizabeth Byosiere

Second Advisor

Dr. Christopher Braun

Academic Program Adviser

Dr. Sandeep Prasada


In recent years, dogs have been a popular test subject when studying visual illusion susceptibility. Multiple studies have investigated whether animals perceive illusions as humans do, but few studies have evaluated dogs’ perception of illusory stimuli. In this thesis, we studied if dogs are visually susceptible to the Ebbinghaus-Titchener illusion when presented in a spontaneous choice task. Subjects were presented two visual images on a board, which had bologna pieces embedded in the stimuli. In control trials, two different sized bologna pieces were placed in the center of the images. In these control conditions, dogs were expected to choose the larger piece of bologna. In test trials, two identical sized bologna pieces were placed in the in the images. If dogs perceive the illusion the way humans do, they were expected to choose the “larger” appearing piece of bologna, which was surrounded by smaller inducer circles. Dogs selected the larger stimulus significantly above chance levels when presented with Control A, however they performed at chance when selecting between the differently sized stimuli in Control B. When presented with the illusion condition, dogs performed at chance indicating null susceptibility of the illusion. These finding suggest that dogs are not susceptible to the Ebbinghaus-Titchener illusion in a spontaneous choice task, contrary to previously observed findings in a training-based paradigm. However, the slightly above chance performance in Control A and at chance performance observed in Control B suggest these results should be interpreted with caution. Additional research should evaluate the suitability of the spontaneous-choice paradigm when evaluating dog illusion susceptibility.



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