Object features used by humans and monkeys to identify rotated shapes.

Humans and rhesus monkeys can identify shapes that have been rotated in the picture plane. Recognition of rotated shapes can be as efficient as recognition of upright shapes. Here we investigate whether subjects showing view-invariant performance use the same object features to identify upright and rotated versions of a shape. We find marked differences between humans and monkeys. While humans tend to use the same features independent of shape orientation, monkeys use unique features for each orientation. Humans are able to generalize to a greater degree across orientation changes than rhesus monkey observers, who tend to relearn separate problems at each orientation rather than flexibly apply previously learned knowledge to novel problems.