Table 1.

Stimulus-response matrices for subjects told to discriminate rotating heads containing views from more than one person (deforming), from real heads containing views from just one person (nondeforming)

Stimulus	Untrained		Trained
	Response		Response
	Deforming	Nondeforming	Deforming	Nondeforming
Deforming	0.687	0.313	0.315	0.685
Nondeforming	0.300	0.700	0.821	0.179

(Untrained) naive subjects were able to select the real heads in preference to the deforming ones (d′ = 1.011). (Trained) Prior exposure to the deforming heads, however, caused subjects to see these heads as nondeforming in preference to the veridical ones (d′ = −1.400).