  Geometric-optical illusions (GOI) are a subclass of a vast variety of visual
illusions. A special class of GOIs originates from the superposition of a
simple geometric figure ("target") with an array of non-intersecting
curvilinear elements ("context") that elicits a perceptual distortion of the
target element. Here we specifically deal with the case of circular targets.
Starting from the fact that (half)circles are geodesics in a model of
hyperbolic geometry, we conceive of the deformations of the target as resulting
from a context-induced perturbation of that "base" geometry. We present
computational methods for predicting distorted shapes of the target in
different contexts, and we report the results of a psychophysical pilot
experiment with eight subjects and four contexts to test the predictions.
Finally, we propose a common scheme for modeling GOIs associated with more
general types of target curves, subsuming those studied previously.
