Abstract: DESCRIPTION (provided by applicant):
Visual object recognition is central to our behavior, and knowledge of the underlying brain mechanisms is critical to understanding human visual perception and memory. The key problem is creation of selectivity for object identity that tolerates changes in an object's retinal image, such as changes in position and size. The primate brain appears to construct this selectivity in the ventral visual stream because neuronal responses in the highest area of that stream--the anterior inferotemporal cortex (AIT)--show shape selectivity that can tolerate position and size changes. Yet, we do not understand these key neuronal properties--reports of AIT tolerance are limited and inconsistent, and recent studies show that it can be very restricted. Thus, the goals of this proposal are an understanding of key factors likely to determine AIT position and size tolerance, and to determine if AIT tolerance can explain behavioral tolerance. Our first aim is to systematically determine the position and size tolerance of AIT neuronal shape selectivity for a range of object sets and object training histories. We will establish the relationship of selectivity and AIT position and size tolerance, the interaction of AIT position and size tolerance, and the effect of object-specific training on these relationships. These data will establish neuronal tolerance at the highest level of the primate visual system and provide a much-needed foundation for further study. The mechanisms that might underlie position and size tolerance fall into two broad classes: (1) automatic generalization; and (2) tolerance learned by experiencing objects across changes in position and size. Our second aim is to determine if position- or size-specific object experience have substantial effects on the position or size tolerance of AIT shape selectivity. Because this has not been examined, any result would be extremely informative in constraining mechanisms and guiding future studies.
Although it is thought that AIT tolerance underlies behavioral tolerance, this has not been systematically examined. Our third aim is to determine if the position and size tolerance of object identification can be explained by the tolerance of AIT neuronal shape selectivity. This is a vital to understanding the link between high-level, ventral stream neuronal responses and visual object identification.

Thesaurus Terms:
brain mapping, cerebral cortex, neural information processing, visual perception
behavioral habituation /sensitization, conditioning, experience, neuron, size perception, space perception, visual threshold
Macaca mulatta, behavior test, behavioral /social science research tag, single cell analysis

Institution: MASSACHUSETTS INSTITUTE OF TECHNOLOGY
77 MASSACHUSETTS AVE
CAMBRIDGE, MA 02139
Fiscal Year: 2006
Department: NONE
Project Start: 01-APR-2004
Project End: 31-MAR-2009
ICD: NATIONAL EYE INSTITUTE
IRG: CVP

The Journal of Neuroscience, September 7, 2005, 25(36):8150-8164

Multiple Object Response Normalization in Monkey Inferotemporal Cortex
 
Davide Zoccolan,^1,2,3 * David D. Cox,^{1,2 *} and James J. DiCarlo<sup>1,2

1</sup>McGovern Institute for Brain Research, ²Department of Brain and Cognitive Sciences, and ³Center for Biological and Computational Learning, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

Animals and surgery
Experiments were performed on three male rhesus monkeys (Macaca mulatta) weighing 8, 9.5, and 10 kg. Before behavioral training, aseptic surgery was performed to attach a head post to the skull of each monkey and to implant a scleral search coil in the right eye of monkeys 1 and 2. After 2–5 months of behavioral training (below), a second surgery was performed to place a recording chamber (18 mm diameter) to reach the anterior half of the left temporal lobe (chamber Horsley-Clark center, 15 mm anterior). All animal procedures were performed in accord with National Institute of Health guidelines and the Massachusetts Institute of Technology Committee on Animal Care.

Eye position monitoring
Horizontal and vertical eye positions were monitored using the scleral search coil (monkeys 1 and 2) or a 250 Hz camera-based system (monkey 3; EyeLink II; SR Research, Osgode, Ontario, Canada). Each channel was digitally sampled at 1 kHz. Methods for detecting saccades and calibrating retinal locations with monitor locations are described in detail previously (DiCarlo and Maunsell, 2000 ).

Behavioral task and training
All three monkeys were trained to fixate a central point (0.2 x 0.2°) for several seconds while a series of visual stimuli were presented in rapid succession (rapid, passive viewing paradigm). In particular, stimulus conditions were presented in a random sequence in which each stimulus condition was on for 100 ms, followed by 100 ms of a gray screen (no stimulus), followed by another stimulus conditions for 100 ms, etc. (see Fig. 1 E). That is, stimulus conditions were presented at a rate of five per second. At this presentation rate, IT neurons show robust object selectivity (Keysers et al., 2001 ), and this rate is consistent with that produced spontaneously by free-viewing monkey (DiCarlo and Maunsell, 2000 ). Single, pair, and triplet object conditions were pseudorandomly interleaved (see schematic in Fig. 1 E). The screen background was always kept at a constant gray. The total number of stimulus conditions presented on each fixation trial ranged from 3 to 20, and the monkey was rewarded for maintaining fixation throughout the trial (±0.5° fixation window in monkeys 1 and 2; ±1.5° fixation window in monkey 3). Failures to maintain fixation throughout the trial resulted in the trial being aborted, and all stimulus conditions in that trial were re-presented.