Learning to tell apples from oranges.

Recognizing images requires sorting them into the correct perceptual categories. Without categories, apples could not be discriminated from oranges. A fundamental question is whether categories are innate or learned, and if learned, how well such discriminations generalize. A recent finding by Notman et al. demonstrates that certain categorical discriminations are learned fast but vanish for slightly rotated stimuli. Rather than higher "cognitive" learning, this indicates involvement of "early" mechanisms, which cannot generalize across different stimulus orientations.