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409
Cortical regions involved in perceiving object shape
- Journal of Neuroscience
, 2000
"... The studies described here use functional magnetic resonance imaging to test whether common or distinct cognitive and/or neural mechanisms are involved in extracting object structure from the different image cues defining an object’s shape, such as contours, shading, and monocular depth cues. We fou ..."
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Cited by 148 (12 self)
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The studies described here use functional magnetic resonance imaging to test whether common or distinct cognitive and/or neural mechanisms are involved in extracting object structure from the different image cues defining an object’s shape, such as contours, shading, and monocular depth cues. We found overlapping activations in the lateral and ventral occipital cortex [known as the lateral occipital complex (LOC)] for objects defined by different visual cues (e.g., grayscale photographs and line drawings) when each was compared with its own scrambled-object control. In a second experiment we found a reduced response when objects were repeated, independent of whether they appeared in the same or a different format (i.e., grayscale images vs line drawings). A third experiment showed that activation in the LOC was no stronger for threedimensional shapes defined by contours or monocular depth
The time course of visual processing : from early perception to decision making
- J. Cogn. Neuroscience,in
, 2001
"... & Experiments investigating the mechanisms involved in visual processing often fail to separate low-level encoding mechanisms from higher-level behaviorally relevant ones. Using an alternating dual-task event-related potential (ERP) experimental paradigm (animals or vehicles categorization) wher ..."
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Cited by 144 (15 self)
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& Experiments investigating the mechanisms involved in visual processing often fail to separate low-level encoding mechanisms from higher-level behaviorally relevant ones. Using an alternating dual-task event-related potential (ERP) experimental paradigm (animals or vehicles categorization) where targets of one task are intermixed among distractors of the other, we show that visual categorization of a natural scene involves different mechanisms with different time courses: a perceptual, task-independent mechanism, followed by a taskrelated, category-independent process. Although average ERP responses reflect the visual category of the stimulus shortly after visual processing has begun (e.g. 75±80 msec), this difference is not correlated with the subject's behavior until 150 msec poststimulus. &
Specialization within the ventral stream: the case for the visual word form area
, 2004
"... nce is often relative rather than absolute. We conclude that learning to read results in the progressive development of an inferotemporal region increasingly responsive to visual words, which is aptly named the visual word form area (VWFA). D 2004 Elsevier Inc. All rights reserved. Keywords: Word ..."
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Cited by 129 (14 self)
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nce is often relative rather than absolute. We conclude that learning to read results in the progressive development of an inferotemporal region increasingly responsive to visual words, which is aptly named the visual word form area (VWFA). D 2004 Elsevier Inc. All rights reserved. Keywords: Word recognition; Occipitotemporal; Specialization Introduction The efficiency of reading in literate adults rests on the ability to quickly identify visual words across large variations of irrelevant parameters such as position, size, color, font, or case. This perceptual expertise requires no less than 5 years of academic training in a specific writing system (Aghababian and Nazir, 2000). The outcome of this perceptual normalization process is an abstract representation of letter identities that has been termed the visual word form (Riesenhuber and Poggio, 1999; Warrington and Shallice, 1980). We formulated the idea that an area in the midportion of the left fusiform gyrus, which activates wh
Category-specific visual responses of single neurons in the human medial temporal lobe.
- Nature Neuroscience ,
, 2000
"... articles Visual recognition of objects is a key function of the primate brain. There is a progression in the complexity of the representation of the visual scene by single neurons. Neurons in early visual areas in monkeys are tuned to simple features of the stimuli, such as the orientation of bars ..."
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Cited by 124 (15 self)
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articles Visual recognition of objects is a key function of the primate brain. There is a progression in the complexity of the representation of the visual scene by single neurons. Neurons in early visual areas in monkeys are tuned to simple features of the stimuli, such as the orientation of bars in area V1 or direction of motion in area V5. In the monkey inferotemporal cortex (IT), neurons respond to complex stimuli, including faces and hands, but also abstract patterns or common, everyday objects 1-3 . There are strong projections from IT to higher association areas in the temporal lobe, including the parahippocampal gyrus, perirhinal cortex, entorhinal cortex, hippocampus and amygdala Temporal lobe lesions lead to profound category-specific deficits in visual recognition in both macaques and humans We reported that neurons in the human medial temporal lobe discriminate objects from faces 21 . Here we further investigated visual response properties and showed that single neurons respond selectively to different stimulus categories. RESULTS We recorded the activity of 427 single neurons in 11 patients with pharmacologically resistant epilepsy who had intracranial depth electrodes implanted to determine the location of the seizure focus for possible surgical resection. Based on clinical criteria, electrode probes, containing several microwires each, were placed in medial temporal lobe targets bilaterally ( Visual responses Most neurons showed maintained firing rates below 10 spikes per second We studied the responses of each neuron to the 1000-ms presentation of the visual stimuli by averaging the activity for all images within each category. For each neuron and each category, a post-stimulus time histogram was computed, showing the neuronal response starting 1000 ms before stimulus onset and ending 1000 ms after the stimulus disappeared. A neuron was considered visually selective for a specific category if the activity during stimulus presentation for that category was significantly different from the baseline activity and from the responses to other categories of stimuli (Methods
Image-Based Object Recognition in Man, Monkey and Machine
, 1998
"... Theories of visual object recognition must solve the problem of recognizing 3D objects given that perceivers only receive 2D patterns of light on their retinae. Recent findings from human psychophysics, neurophysiology and machine vision provide converging evidence for `image-based' models i ..."
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Cited by 123 (8 self)
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Theories of visual object recognition must solve the problem of recognizing 3D objects given that perceivers only receive 2D patterns of light on their retinae. Recent findings from human psychophysics, neurophysiology and machine vision provide converging evidence for `image-based' models in which objects are represented as collections of viewpoint-specific local features. This approach is contrasted with `structural-description' models in which objects are represented as configurations of 3D volumes or parts. We then review recent behavioral results that address the biological plausibility of both approaches, as well as some of their computational advantages and limitations. We conclude that, although the image-based approach holds great promise, it has potential pitfalls that may be best overcome by including structural information. Thus, the most viable model of object recognition may be one that incorporates the most appealing aspects of both image-based and structural-description theories. 1998 Elsevier Science B.V. All rights reserved Keywords: Object recognition; Image-based model; Structural description 1.
Invariant Object Recognition in the Visual System with Novel Views of 3D Objects
, 2002
"... ... In this article, we show how trace learning could solve the problem of in-depth rotation-invariant object recognition by developing representations of the transforms that features undergo when they are on the surfaces of 3D objects. Moreover, we show that having learned how features on 3D object ..."
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Cited by 111 (17 self)
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... In this article, we show how trace learning could solve the problem of in-depth rotation-invariant object recognition by developing representations of the transforms that features undergo when they are on the surfaces of 3D objects. Moreover, we show that having learned how features on 3D objects transform geometrically as the object is rotated in depth, the network can correctly recognize novel 3D variations within a generic view of an object composed of a new combination of previously learned features. These results are demonstrated in simulations of a hierarchical network model (VisNet) of the visual system that show that it can develop representations useful for the recognition of 3D objects by forming perspective-invariant representations to allow generalization within a generic view.
A rose by any other name: Long term memory structure and sentence processing
- Journal of Memory and Language
, 1999
"... The effects of sentential context and semantic memory structure during on-line sentence processing were examined by recording event-related brain potentials as individuals read pairs of sentences for comprehension. The first sentence established an expectation for a particular exemplar of a semantic ..."
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Cited by 101 (15 self)
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The effects of sentential context and semantic memory structure during on-line sentence processing were examined by recording event-related brain potentials as individuals read pairs of sentences for comprehension. The first sentence established an expectation for a particular exemplar of a semantic category, while the second ended with (1) that expected exemplar, (2) an unexpected exemplar from the same (expected) category, or (3) an unexpected item from a different (unexpected) category. Expected endings elicited a positivity between 250 and 550 ms while all unexpected endings elicited an N400, which was significantly smaller to items from the expected category. This N400 reduction varied with the strength of the contextually induced expectation: unexpected, categorically related endings elicited smaller N400s in more constraining contexts, despite their poorer fit to context (lower plausibility). This pattern of effects is best explained as reflecting the impact of context-independent long-term memory structure on sentence processing. The results thus suggest that physical and functional similarities that hold between objects in the world—i.e., category structure—influence neural organization and, in turn, routine language comprehension processes. © 1999 Academic Press Key Words: sentence processing; categorization; event-related potentials; N400. At its heart, language comprehension involves
Comparison of primate prefrontal and inferior temporal cortices during visual categorization
- J. Neurosc
, 2003
"... Previous studies have suggested that both the prefrontal cortex (PFC) and inferior temporal cortex (ITC) are involved in high-level visual processing and categorization, but their respective roles are not known. To address this, we trained monkeys to categorize a continuous set of visual stimuli int ..."
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Cited by 94 (14 self)
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Previous studies have suggested that both the prefrontal cortex (PFC) and inferior temporal cortex (ITC) are involved in high-level visual processing and categorization, but their respective roles are not known. To address this, we trained monkeys to categorize a continuous set of visual stimuli into two categories, “cats ” and “dogs. ” The stimuli were parametrically generated using a computer graphics morphing system (Shelton, 2000) that allowed precise control over stimulus shape. After training, we recorded neural activity from the PFC and the ITC of monkeys while they performed a category-matching task. We found that the PFC and the ITC play distinct roles in category-based behaviors: the ITC seems more involved in the analysis of currently viewed shapes, whereas the PFC showed stronger category signals, memory effects, and a greater tendency to encode information in terms of its behavioral meaning. Key words: categorization; monkey; vision; object vision; inferior temporal cortex; prefrontal cortex; learning
Single units and conscious vision
- Philos Trans R Soc Lond B Biol Sci
, 1998
"... Figures that can be seen in more than one way are invaluable tools for the study of the neural basis of visual awareness, because such stimuli permit the dissociation of the neural responses that underlie what we perceive at any given time from those forming the sensory representation of a visual pa ..."
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Cited by 69 (1 self)
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Figures that can be seen in more than one way are invaluable tools for the study of the neural basis of visual awareness, because such stimuli permit the dissociation of the neural responses that underlie what we perceive at any given time from those forming the sensory representation of a visual pattern. To study the former type of responses, monkeys were subjected to binocular rivalry, and the response of neurons in a number of di¡erent visual areas was studied while the animals reported their alternating percepts by pulling levers. Perception-related modulations of neural activity were found to occur to di¡erent extents in di¡erent cortical visual areas. The cells that were a¡ected by suppression were almost exclusively binocular, and their proportion was found to increase in the higher processing stages of the visual system. The strongest correlations between neural activity and perception were observed in the visual areas of the temporal lobe. A strikingly large number of neurons in the early visual areas remained active during the perceptual suppression of the stimulus, a ¢nding suggesting that conscious visual perception might be mediated by only a subset of the cells exhibiting stimulus selective responses. These physiological ¢ndings, together with a number of recent psychophysical studies, o¡er a new explanation of the phenomenon of binocular rivalry. Indeed, rivalry has long been considered to be closely linked with binocular fusion and stereopsis, and the sequences of dominance and suppression have been viewed as the result of competition between the two monocular channels. The physiological data presented here are incompatible with this interpretation. Rather than re£ecting interocular competition, the rivalry is most probably between the two di¡erent central neural representations generated by the dichoptically presented stimuli. The mechanisms of rivalry are probably the same as, or very similar to, those underlying multistable perception in general, and further physiological studies might reveal much about the neural mechanisms of our perceptual organization.
Patterns of activity in the categorical representations of objects
- J. Cogn. Neurosci
, 2002
"... & Object perception has been a subject of extensive fMRI studies in recent years. Yet, the nature of the cortical representation of objects in the human brain remains controversial. Analyses of fMRI data have traditionally focused on the activation of individual voxels associated with presentati ..."
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Cited by 68 (1 self)
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& Object perception has been a subject of extensive fMRI studies in recent years. Yet, the nature of the cortical representation of objects in the human brain remains controversial. Analyses of fMRI data have traditionally focused on the activation of individual voxels associated with presentation of various stimuli. The current analysis approaches functional imaging data as collective information about the stimulus. Linking activity in the brain to a stimulus is treated as a pattern-classification problem. Linear discriminant analysis was used to reanalyze a set of data originally published by Ishai et al. (2000), available from fMRIDC (accession no. 2-2000-1113D). Results of the new analysis reveal that patterns of activity that distinguish one category of objects from other categories is largely independent of one another, both in terms of the activity and spatial overlap. The information used to detect objects from phase-scrambled control stimuli is not essential in distinguishing one object category from another. Furthermore, performing an object-matching task during scan significantly improved the ability to predict objects from controls, but had minimal effect on object classification, suggesting that the task-based attentional benefit was nonspecific to object categories. &
