Translation Invariance in Object Recognition, and Its Relation to Other Visual Transformations

Human object recognition is generally considered to tolerate changes of the stimulus position in the visual eld. A number of recent studies, however, have cast doubt on the completeness of translation invariance. In a new series of experiments we tried to investigate whether positional speciicity of short-term memory is a general property of visual perception. We tested same-diierent discrimination of computer graphics models that were displayed at the same or at diierent locations of the visual eld, and found complete translation invariance, regardless of the similarity of the animals and irrespective of direction and size of the displacement (Exp. 1 and 2). Decisions were strongly biased towards same decisions if stimuli appeared at a constant location, while after translation subjects displayed a tendency towards diierent decisions. Even if the spatial order of animal limbs was randomized ("scrambled animals"), no deteriorating eeect of shifts in the eld of view could be detected (Exp. 3). However, if the innuence of single features was reduced (Exp. 4 and 5) small but signiicant eeects of translation could be obtained. Under conditions that do not reveal an innuence of translation, rotation in depth strongly interferes with recognition (Exp. 6). Changes of stimulus size did not reduce performance (Exp. 7). Tolerance to these object transformations seems to rely on diierent brain mechanisms, with translation and scale invariance being achieved in principle, while rotation invariance is not.