Are Judgments of Linear Size More Accurate When Based on an Affordance?

Abstract

Perceptual judgments of size affect a wide variety of activities but can be difficult to measure. Two methods of estimating size (linear extent) were compared. One required adjustment of the distance between a point created by a laser beam and a fixed reference line; the other involved adjusting the separation of 2 vertical posts. Two groups of adults were instructed to use these methods to indicate either simple linear extent ("width") or the affordance of passability (minimal opening) for identical dimensions of objects and their own bodies. Afterward, the participants completed a survey including the Eating Attitudes Test (EAT-26). Accuracy did not vary with instructions or EAT-26 scores. As predicted, accuracy was found to be lower for participants whose body weight had recently changed by 5% or more, presumably due to a less refined attunement to their current body sizes. Higher accuracy was expected for both the method (posts) and instructions ("opening") that should foster affordance-based judgments. Despite the greater ease and precision of the laser-based method, more accurate estimates were made using movable posts. These results are discussed in terms of 2 contrasting perceptual modes.