Background: The inferior temporal cortex (IT) of the monkey has long b
een known to play an essential role in visual object recognition. Dama
ge to this area results in severe deficits in perceptual learning and
object recognition, without significantly affecting basic visual capac
ities. Consistent with these ablation studies is the discovery of IT n
eurons that respond to complex two-dimensional visual patterns, or obj
ects such as faces or body parts. What is the role of these neurons in
object recognition! Is such a complex configurational selectivity spe
cific to biologically meaningful objects, or does it develop as a resu
lt of extensive exposure to any objects whose identification relies on
subtle shape differences? If so, would IT neurons respond selectively
to recently learned views or features oi novel objects? The present s
tudy addresses this question by using combined psychophysical and elec
trophysiological experiments, in which monkeys learned to classify and
recognize computer-generated three-dimensional objects. Results: A po
pulation of IT neurons was found that responded selectively to views o
f previously unfamiliar objects. The cells discharged maximally to one
view of an object, and their response declined gradually as the objec
t was rotated away from this preferred view. No selective responses we
re ever encountered-for views that the animal systematically failed to
recognize. Most neurons also exhibited orientation-dependent response
s during view-plane rotations. Some neurons were found to be tuned aro
und two views of the same object, and a very small number of cells res
ponded in a view-invariant manner. For the five different objects that
were used extensively during the training of the animals, and for whi
ch behavioral performance became view-independent, multiple cells were
found that were tuned around different views of the same object. A nu
mber of view-selective units showed response invariance for changes in
the size of the object or the position of its image within the parafo
vea. Conclusion: Our results suggest that IT neurons can develop a com
plex receptive field organization as a consequence of extensive traini
ng iii the discrimination and recognition of objects. None of these ob
jects had any prior meaning for the animal, nor did they resemble anyt
hing familiar in the monkey's environment. Simple geometric features d
id not appear to account for the neurons' selective responses. These f
indings support the idea that a population of neurons - each tuned to
a different object aspect, and each showing a certain degree of invari
ance to image transformations - may, as an ensemble, encode at least s
ome types of complex three-dimensional objects. In such a system, seve
ral neurons may be active for any given vantage point, with a single u
nit acting like a blurred template for a limited neighborhood of a sin
gle view.