Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Psychological Sciences

First Advisor

Robert W. Proctor

Committee Chair

Robert W. Proctor

Committee Member 1

Ehtibar Dzhafarov

Committee Member 2

Darryl Schneider

Committee Member 3

Richard Schweickert


Several researchers have hypothesized that the hands have unique effects on visual attentional resources and performance in response-selection tasks. This hand-specific processing hypothesis – that biological properties of the hands/palms uniquely affect visual attention and response selection – can be compared to a referential object coding hypothesis – that objects are coded in relation to other salient objects – favored in explanations of many compatibility effects. To test implications of these accounts, and specific effects that the hands (or general referential objects) have on attentional prioritization, I had participants perform three compatibility tasks using the hands or wooden blocks as referential objects. These objects were placed on a display screen such that they meaningfully segmented the space appropriate to response selection or in a position below the screen where they did not segment the space. Participants responded with a left or right foot-press response in all tasks, so that position of the response effectors was not confounded with that of the hands.

The Simon task evaluated whether hands differently affected the processes of selecting the correct response when the task was stimulus-property dependent: That is to say, the goal of a left/right response was determined by a mapping of color to response. In the Simon task, a purple or orange circle appeared in the left or right location of the screen, each color mapped to a left or right response. Hands were placed such that either the left or the right hand was positioned at the middle of the screen or at the bottom of the screen (in separate blocks). The Stimulus-Response Compatibility (SRC) task utilized the same methodology, but rather than mapping color to response, participants were instructed to respond in separate trial blocks with the response at the same or opposite side as the stimulus. The SRC task evaluated specifically the effect of task instructions on the response selection and attentional processes. Thus, the Simon and SRC tasks together determined the effects of referential objects on attending to relevant features of the stimulus and improving performance when instructions, themselves, need to be attended.

Finally, the Stroop task tested one’s ability to attend to the appropriate stimulus in an array of salient distractors. In the Stroop task, participants responded to the color of a bar presented on the screen along with congruent or incongruent color words. The bar could occur at the peripheral locations or centrally. Hands were positioned such that they either segmented the display, separating the targets from the distractors, or did not do soe (being placed below the screen). The Stroop task evaluated the impact on attention from distractors located in the visual array.

Across tasks, there was a reduction in the interference from incompatible/incongruent information when the hands and wooden blocks meaningfully segmented the display versus when they were located below it. This suggests a benefit of attentional focusing that occurs in the presence of meaningful referential objects which are positioned in such a way that response selection can occur in relation to them. That the hands and wooden blocks demonstrated similar effects suggests this referential coding is a more general effect and not specific to the hands. Finally, there were no differences when evaluating stimuli near the palm versus the back of the hands, which suggests the biological properties of the palms are not unique in attentional processes during response selection across compatibility tasks.

The experiments demonstrate two unique findings: 1) Hands and other referential objects effectively improve response-selection performance across a variety of compatibility tasks by reducing the impact of distracting information; 2) contrary to hypotheses regarding biological properties of the palms of the hands, responding to stimuli near the palms is not unique when a referential object meaningfully segments the display. Thus, referential objects seem to improve performance when their position segments the display to match the responses being selected.

Included in

Psychology Commons