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We compared neural substrates of two-dimensional shape processing in human and nonhuman primates using functional magnetic resonance (MR) imaging in awake subjects. The comparison of MR activity evoked by viewing intact and scrambled images of objects revealed shape-sensitive regions in occipital, temporal, and parietal cortex of both humans and macaques.(More)
To reduce the information gap between human neuroimaging and macaque physiology and anatomy, we mapped fMRI signals produced by moving and stationary stimuli (random dots or lines) in fixating monkeys. Functional sensitivity was increased by a factor of approximately 5 relative to the BOLD technique by injecting a contrast agent (monocrystalline iron oxide(More)
The extent to which object identification is influenced by the background of the scene is still controversial. On the one hand, the global context of a scene might be considered as an ultimate representation, suggesting that object processing is performed almost systematically before scene context analysis. Alternatively, the gist of a scene could be(More)
Stereopsis, the perception of depth from small differences between the images in the two eyes, provides a rich model for investigating the cortical construction of surfaces and space. Although disparity-tuned cells have been found in a large number of areas in macaque visual cortex, stereoscopic processing in these areas has never been systematically(More)
Iron oxide contrast agents have been employed extensively in anesthetized rodents to enhance fMRI sensitivity and to study the physiology of cerebral blood volume (CBV) in relation to blood oxygen level-dependent (BOLD) signal following neuronal activation. This study quantified the advantages of exogenous agent for repeated neuroimaging in awake, nonhuman(More)
The present report reviews a series of functional magnetic resonance imaging (fMRI) activation studies conducted in parallel in awake monkeys and humans using the same motion stimuli in both species. These studies reveal that motion stimuli engage largely similar cortical regions in the two species. These common regions include MT/V5 and its satellites, of(More)
Using functional magnetic resonance imaging (fMRI), we mapped the retinotopic organization throughout the visual cortex of fixating monkeys. The retinotopy observed in areas V1, V2, and V3 was completely consistent with the classical view. V1 and V3 were bordered rostrally by a vertical meridian representation, and V2 was bordered by a horizontal meridian.(More)
This study aimed to determine the extent to which rapid visual context categorization relies on global scene statistics, such as diagnostic amplitude spectrum information. We measured performance in a Natural vs. Man-made context categorization task using a set of achromatic photographs of natural scenes equalized in average luminance, global contrast, and(More)
Whereas most scientists agree that scene context can influence object recognition, the time course of such object/context interactions is still unknown. To determine the earliest interactions between object and context processing, we used a rapid go/no-go categorization task in which natural scenes were briefly flashed and subjects required to respond as(More)
Humans are fast and accurate at performing an animal categorization task with natural photographs briefly flashed centrally. Here, this central categorization task is compared to a three position task in which photographs could appear randomly either centrally, or at 3.6 degrees eccentricity (right or left) of the fixation point. A mild behavioral(More)