Imperfect invariance to object translation in the discrimination of complex shapes

The positional specificity of short-term visual memory for a variety of 3-D shapes was investigated in a series of 'same'/'different' discrimination e xperiments, with computer-rendered stimuli displayed either at the same or at different locations in the visual field. For animal-like shapes, we Foun d complete translation invariance, regardless of the interstimulus similari ty, and irrespective of direction and size of the displacement (experiments 1 and 2). Invariance to translation was obtained also with animal-like sti muli that had been 'scrambled' by randomizing the relative locations of the ir parts (experiment 3). The invariance broke down when the stimuli were ma de to differ in their composition. but not in the shapes of the correspondi ng parts (experiments 4 and 5). We interpret this pattern of findings in th e context of several current theories of recognition, focusing in particula r on the issue of the representation of object structure.