Date of Award


Degree Type


Degree Name

Master of Science


Psychological Science


Psychological Science (MS)

First Advisor/Chairperson

Mounia Ziat


The Ebbinghaus Illusion (also known as Titchener's circles) is a classic visual illusion. The illusion consists of two inner circles of the same size, with one circle surrounded by a group of larger circles, and the other circle surrounded by a group of smaller circles. Due to the context of the surrounding circles, individuals perceive the inner circle surrounded by the smaller outer circles to be larger, when in fact, both inner circles are the same size. This thesis presents the first evidence of the existence of the Ebbinghaus illusion in the tactile modality. Participants underwent various tactile-tactile and tactile-visual conditions to actively explore Ebbinghaus illusion sets. Our results show that participants are more likely to be deceived when the illusory stimulus (the Ebbinghaus set) is present compared to when the control stimulus (no illusion) is present in a tactile perception condition. Further, our results demonstrate that in a visual-tactile condition, the perceptual system is not deceived, even though the illusion deceives participants in both touch and vision alone. These results contribute to the two-stream hypothesis perception-action debate, which states that the pathways for action and perception are separated in the visual system.

Access Type

Open Access

Included in

Psychology Commons