The Role of Affordance Perception in Action-selection

The selection of goal-directed actions is based on a prospective consideration of possible action outcomes. Traditional accounts of this process have routinely postulated the involvement of some internal, decision-making faculty--for example, a pattern generator, action plan, knowledge structures, or internal model that is responsible for the a priori selection, and subsequent organization and regulation of goal-directed action. An alternative account, as proposed by advocates of embodied cognition and ecological psychology (Araújo, Davids, & Hristovski, 2006; Cisek, 2007; Spivey, 2007), proposes that the selection and execution of action occur simultaneously in a unified process. This process is not prescribed, per se, but is guided by the continuous perception of affordances (Gibson, 1986), the perceived opportunities for action that exist by virtue of the actors' functional relation to their surrounding environment. In this spirit, the present dissertation investigated the role of layout of affordances in action-selection. At any given moment, distinct opportunities for action abound, each varying in degree of desirability or optimality given the intentions of the actor. When multiple affordances present alternate routes to a desired goal, a "competition" may ensue until one is ultimately selected above all others (Cisek, 2007). This competition not only may influence the likelihood that one particular action is selected, but also has been demonstrated to affect the time-course evolution of a response: corresponding to increases in response latency, response time, and the deviation in response trajectory during dual choice tasks (e.g., Anderson, Matlock, & Spivey, 2010; Dale, Kehoe, & Spivey, 2007). Over three experiments, participants were charged with moving a virtual "ball" across a table to a highlighted goal location, in the process passing through a barrier wall via one of two apertures. The layout of affordances in this virtual environment was manipulated by varying the width of each independent aperture relative to the width of the ball, as well as the proximity of each aperture to the goal. Both manipulations resulted in systematic changes in the distribution of response outcomes--participants were more likely to select the larger aperture (Experiment 1) or the aperture that provided the more direct route to the goal (Experiment 2). Systematic changes were also observed in competition measures: increases in movement time and deflection of the reach trajectory where observed in conditions where there was increased ambiguity as to which aperture afforded passing through. Thus, the confluence of aperture width and proximity to the goal influenced the online selection and evolution of action--participants' responses reflected the least amount of competition when spatial proximity between the location of the goal and an aperture that afforded passage (or affordance-destination compatibility) indicated a direct route. Experiment 3 investigated the influence of affordance-destination compatibility on transitions between behavioral modes, where relative proximity to the goal influenced the both the likelihood and point at which participants transitioned from selecting one aperture to the other. These results were taken as further support of the influence of perceived affordance-destination compatibility in action selection.