Response competition operates on movement direction and is effector-independent: Evidence from three free choice reaching tasks

• Author / Creator

  Atkin, Alice

• People and other organisms live in complex environments where the number of potential actions is almost always greater than the number of actions that can be performed at a time. Thus, organisms must make decisions about which actions to perform and which to not perform. Theories about how action decisions occur fall into two broad categories: serial and parallel. Serial theories claim that a decision about which action to perform is made before the movements required to complete the action are specified; thus, only one action is ever planned at a time. In contrast, parallel theories claim that movements can be specified prior to such a decision, resulting in two or more potential actions being planned simultaneously. The affordance competition hypothesis, proposed by Paul Cisek in 2007, is a parallel theory which claims that actions are decided upon via competitive process between movement plans. The novelty of this hypothesis is that it proposes a starring role for the “motor” system in the decision-making process, eliminating the need for any sort of dedicated “decision system”. According to Cisek, movement planning is not the outcome of decision-making, but is instead the basis for it. Most of the experiments designed to test this hypothesis, however, involve cued actions rather than actions which are chosen endogenously by the participant. Cued actions are comparatively rare outside of lab conditions, with the majority of actions performed voluntarily according to an individual’s internal motives. In this thesis, I report three experiments which were intended to test the affordance competition hypothesis under the more ecologically relevant condition of allowing participants to choose their actions rather than having actions chosen for them. Experiment 1 established the basic procedure of the thesis project, with participants being presented with a small, circular target in one of several possible lateralized locations, then given the choice of reaching out and touching the target with either their left hand or their right hand. In this experiment, participants responded more slowly to targets near the center of the screen, where the likelihood of using each hand was roughly equal, than they did to more lateralized targets where one hand performed the vast majority of responses. In Experiment 2, each target was preceded by a fixation cross in one of two possible lateralized locations. This arrangement required participants to perform both eye and hand movements to each target without making those movement directions necessarily congruent. Participants responded faster during trials where the eye and hand movements were congruent versus incongruent trials. In Experiment 3, a cue condition was added in order to explicitly contrast the results of Experiments 1 and 2 against results obtained under this more common experimental condition. Unlike voluntary actions, which were slower to central targets just as they were in Experiment 1, cued actions were actually performed faster to central targets, and were also performed more accurately overall. In line with the affordance competition hypothesis, the results of these three experiments suggest that people engage in a process of movement competition based on movement direction during voluntary actions. The results also suggest that voluntary and cued actions exhibit unique neurological and kinematic characteristics.

• Subjects / Keywords

  • Reference Frame
  • Competition
  • Volition
  • Decision Making
  • Motor Control
  • Affordance
  • Reaching
  • Vision

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3FB4X298

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.