Neurophysiological studies have shown that some neurons in the cortex in the superior temporal sulcus and in the inferior temporal cortex respond to faces. To determine if some face responsive neurons encode stimuli in an object-centered coordinate system rather than a viewer-centered coordinate system, a large number of neurons were tested for sensitivity to head movement in 3 macaque monkeys. Ten neurons responded only when a head undergoing rotatory movements was shown. All of these responded to a particular movement independently of the orientation of the moving head in relation to the viewer, maintaining specificity even when the moving head was inverted or shown from the back, thereby reversing viewer-centered movement vectors. This was taken as evidence that the movement was encoded in object-centered coordinates. In tests of whether there are neurons in this area which respond differently to the faces of different individuals relatively independently of viewing angle, it was found that a further 18 neurons responded more to one static face than another across different views. However, for 16 of these 18 cells there was still some modulation of the neuronal response with viewing angle. These 16 neurons thus did not respond perfectly in relation to the object shown independently of viewing angle, and may represent an intermediate stage between a viewer-centered and an object-centered representation. In the same area as these neurons, other cells were found which responded on the basis of viewer-centered coordinates. These neurophysiological findings provide evidence that some neurons in the inferior temporal visual cortex respond to faces (or heads) on the basis of object-centered coordinates, and that others have responses which are intermediate between object-centered and viewer-centered representations. The results are consistent with the hypothesis that object-centered representations are built in the inferior temporal visual cortex.

Neurophysiological studies have shown that some neurons in the cortex in the superior temporal sulcus and the inferior temporal gyrus of macaque monkeys respond to faces. These neurons provided a consistently identifiable substrate with which studies of the storage of visual information were performed. To determine whether face responsive neurons change how much they respond to different novel faces as they become familiar, neurons were tested with two experimental designs. In the first experiment, 22 neurons were tested on their responsiveness to the different members of a large set of novel faces as the set was presented repeatedly until the faces became familiar. 6 neurons altered the relative degree to which they responded to the different members of the set between the first two presentations and subsequent presentations. In a control condition, only 1 out of 17 neurons showed a significant response difference between the first two presentations and subsequent presentations when the experiment started with faces which were already familiar to the monkey. In the second experiment, 26 neurons were tested on their responsiveness to the different members of a set of familiar faces before and after the addition of a novel face to the set. 5 neurons altered the relative degree in which they responded to the different members of the set of familiar faces after addition of a novel face. It is suggested that these changes in neuronal responsiveness to different stimuli reflect the setting up of an ensemble encoded representation of face stimuli. This alteration of neuronal responsiveness as novel faces become familiar suggests that face responsive neurons may store information useful in visual recognition. In addition to this relatively long-term alteration of relative neuronal responsiveness to different stimuli, it was found that a large number of cells showed a higher mean response to the first presentation of a set of novel faces than to subsequent presentations of the faces. However, the response to the first presentation of a set of familiar faces was also higher than to subsequent presentations in that sequence. This pattern indicates a short term recency effect in the response of these neurons to visual stimuli which is similar to that previously reported (Baylis and Rolls 1987).

Adult monkeys with late temporal lobe damage are known to touch and mouth objects compulsively, even unknown objects. To determine whether infants with early temporal damage display this symptom as well, 9-month-old rhesus monkeys with neonatal ablations of either the medial temporal lobe or inferior temporal cortex were exposed to four objects, two familiar and two novel. All operated infants were less active/more withdrawn than controls and showed neither exaggerated object manipulation nor hyperorality. Furthermore, like controls, they touched novel objects less than they touched familiar ones. Thus, infants with neonatal medial or inferior temporal ablations did not display the compulsive exploration evidenced after similar lesions in adulthood and retained some ability to detect novelty despite their known memory impairments.

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Six rats bar-pressed for intracranial self-stimulation in a Skinner box on fixed interval and differential reinforcement of low rate schedules with an interval parameter of 1.3 s. After amphetamine timing efficiency was reduced immediately on both the schedules; it recovered after 60 min on the DRL schedule but not within 120 min on the FI schedule. Response rates increased on both the schedules. The increased response rates correlated with the low efficiency on the DRL but not on the FI schedule. The selective sparing of DRL performance is in line with the similarity between the effects of amphetamine and frontal cortical lesions.