This study examined perceptual adaptation to nonplanar (spherical convex and aspheric) rearview mirrors. Subjects made magnitude estimates of the distance to a car seen in a rearview mirror. Three different mirrors were used: plane, aspheric (with a large spherical section having a radius of 1400 mm), and simple convex (with a radius of 1000 mm).
Previous research relevant to perceptual adaptation to nonplanar mirrors was reviewed. It was argued that, in spite of some cases of explicit interest in the process of learning to use nonplanar mirrors, previous research has not adequately addressed the possibility of perceptual adaptation.
The present experiment involved three phases: (1) a pretest phase in which subjects made distance judgments but received no feedback, (2) a training phase in which they made judgments and did receive feedback, and (3) a posttest phase with the same procedure as the pretest phase.
Initially subjects showed substantial overestimation of distance with the convex mirror relative to the aspheric mirror, and with the aspheric mirror relative to the plane mirror. At the beginning of the training phase, overestimation with the convex mirror quickly diminished, but after about one hour of experience the convex and aspheric mirrors still showed significant overestimation relative to the plane mirror.
The present results demonstrate the existence of a rapid, but incomplete, form of adaptation. Whether there is a further mechanism that might operate over a longer time, but lead to more complete adaptation, is an open question that should be addressed by further research. Future research should also address the question of what forms of experience or training are most conducive to adaptation. If substantial adaptation is indeed possible, the use of nonplanar rearview mirrors would be strongly encouraged.