Date of Award

Summer 8-1-2021

Degree Type


Degree Name

Doctor of Philosophy (PhD)



Committee Chair

Dr. Alen Hajnal

Committee Chair School


Committee Member 2

Dr. Mark Huff

Committee Member 2 School


Committee Member 3

Dr. Aaron Fath

Committee Member 3 School


Committee Member 4

Dr. Richard Mohn

Committee Member 4 School



How does the relationship between an actor’s body proportions (eye-, shoulder-, and arm length) and environmental properties (object distance) affect the perception of whether an object is within reach? Experiment 1 demonstrated that participants are more accurate at judging their own eye height than shoulder height. Experiment 2 revealed that participants can accurately perceive the angular direction to a target object’s location. Interestingly, their pointing errors were significantly smaller when measured from the shoulder as a reference point than from the eye. In Experiment 3 we verified this finding using a functionally meaningful affordance task of reaching to a target object. The study tested whether participants rely on a particular complex variable that specifies the target object’s location in space. This variable may serve as an invariant informational pattern that determines what is reachable. In Experiment 3 it was shown that the invariant that includes arm length, body height, and angle of declination to the target successfully predicted affordance judgments, but only when measured from the shoulder as a reference point. Affordance judgments were more accurate using the shoulder than the eye as a reference. Implications for the embodied nature of affordance perception are carefully considered in light of the present evidence.