Estimating the 'reachability' of a line: An affordance perception approach [Estimando la 'alcanzabilidad' de una línea: Una aproximación a la percepción de acción]

Two experiments were conducted to assess the perception of 'reachability' of horizontal lines at different heights in humans. In Experiment 1, participants were asked whether the lines were reachable using their arms, and in Experiment 2 the estimation was made using a pole that was sized at the maximum extension of the participants' arms in vertical position. Two conditions were arranged for both experiments: participants estimated whether the lines were reachable while sitting in a small chair (Low Support Condition) or while sitting in a tall chair (High Support Condition). For data analysis we used a body-scaled or intrinsic metric that is expressed as the ratio of the height of stimuli with respect to the participants' maximum arm extension or respect to the pole's extension. This measurement evaluated the accuracy of the participants' estimation. Results showed that subjects estimated the reachability of the lines more accurately when using their arms (Experiment 1) than when using the pole (Experiment 2); nevertheless, participants had less confidence of their estimations at heights close to the absolute critical boundary. Findings are discussed in terms of the behavioral meaning of stimuli, the intrinsic metric in the affordance perception, and their contribution for the experimental analysis of behavior