The psychophysics of affordance perception: Stevens' power law scaling of perceived maximum forward reachability with an object.

The literatures on affordance perception and psychophysics are seminal in the basic study of perception and action. Nevertheless, the application of classic psychophysical methodologies/analysis to the study of affordance perception remains unexplored. In four experiments, we investigated the Stevens' power law scaling of affordance perception. Participants reported maximum forward reaching ability with a series of rods (both seated and standing) for themselves and another person (confederate). Participants also reported a property of the rod set that has been explored in previous psychophysical experiments and changes in equal measure with forward reach-with-ability (length). In all, we found that affordance perception reports (β = .32) were an underaccelerated function of actual changes in reaching ability compared with relatively less accelerated length reports (β = .73). Affordance perception scaled with stimulus magnitude more similarly to brightness perception than length perception. Furthermore, affordance perception reports scaled similarly regardless of the actor (self and other), task context (seated and standing), or idiosyncrasies of the measurement procedure (controlling for distance compression effects), while length perception reports were sensitive to location/distance compression effects. We offer empirical and theoretical considerations, along with pathways for future research.