The Experts below are selected from a list of 90 Experts worldwide ranked by ideXlab platform
Jon Driver - One of the best experts on this subject based on the ideXlab platform.
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unconscious activation of visual cortex in the damaged right hemisphere of a parietal patient with extinction
Brain, 2000Co-Authors: Geraint Rees, Ewa Wojciulik, Karen Clarke, Masud Husain, C D Frith, Jon DriverAbstract:Visual extinction is a sign classically associated with right parietal damage. The patient can see a single Stimulus presented in the Ipsilesional or contralesional visual field, but is characteristically unaware of the same contralesional Stimulus during simultaneous stimulation of both fields. The Ipsilesional Stimulus is said to `extinguish' the contralesional Stimulus from awareness during bilateral stimulation, perhaps due to a pathological bias in attention towards the Ipsilesional side. Recent psychophysical evidence suggests that, although extinguished stimuli are not consciously seen, they may undergo residual processing and exert implicit effects on performance. However, the neural structures mediating such residual processing for extinguished stimuli remain unknown. Here we studied the neural activity evoked by an extinguished visual Stimulus, using event-related functional MRI (fMRI), in a patient with circumscribed right inferior parietal damage and profound left-sided extinction. Monochrome objects (faces or houses) were presented in the left or right field, either unilaterally or bilaterally on each trial, with the patient indicating by button press whether he saw an object on the left, the right or on both sides. He usually saw only the right object on bilateral trials, yet the fMRI data showed activation of visual cortex contralateral to the extinguished left Stimulus on these trials (compared with right-only stimulation), in both striate and early extrastriate areas of the right hemisphere. This activity had a similar location and time-course to that resulting from a single Stimulus in the left versus right visual field. Cortical pathways involved in the normal processing of a single seen Stimulus can thus still be activated by an unseen, extinguished Stimulus after right parietal damage. Comparison of fMRI responses for faces versus houses revealed some category-specific activation for extinguished stimuli in right fusiform regions, but only at low statistical threshold. These results are discussed in terms of theoretical accounts for parietal extinction and, more generally, for the neural substrates of visual awareness.
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Preattentive Filling-in of Visual Surfaces in Parietal Extinction
Science (New York N.Y.), 1997Co-Authors: Jason B. Mattingley, G Davis, Jon DriverAbstract:Unilateral brain damage frequently produces “extinction,” in which patients can detect brief single visual stimuli on either side but are unaware of a contralesional Stimulus if presented concurrently with an Ipsilesional Stimulus. Explanations for extinction have invoked deficits in initial processes that operate before the focusing of visual attention or in later attentive stages of vision. Preattentive vision was preserved in a parietally damaged patient, whose extinction was less severe when bilateral stimuli formed a common surface, even if this required visual filling-in to yield illusory Kanizsa figures or completion of partially occluded figures. These results show that parietal extinction arises only after substantial processing has generated visual surfaces, supporting recent claims that visual attention is surface-based.
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Preattentive filling-in of visual surfaces in parietal extinction
1997Co-Authors: Jason B. Mattingley, G Davis, Jon DriverAbstract:Unilateral brain damage frequently produces “extinction, ” in which patients can detect brief single visual stimuli on either side but are unaware of a contralesional Stimulus if presented concurrently with an Ipsilesional Stimulus. Explanations for extinction have invoked deficits in initial processes that operate before the focusing of visual attention or in later attentive stages of vision. Preattentive vision was preserved in a parietally damaged patient, whose extinction was less severe when bilateral stimuli formed a common surface, even if this required visual filling-in to yield illusory Kanizsa figures or completion of partially occluded figures. These results show that parietal extinction arises only after substantial processing has generated visual surfaces, supporting recent claims that visual attention is surface-based. A key feature of vision is that Stimulus events receive substantial processing before being selectively attended. Theories of nor-mal vision have suggested that properties such as color, shape, and motion are code
P. Vuilleumier - One of the best experts on this subject based on the ideXlab platform.
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Perceived gaze direction in faces and spatial attention: a study in patients with parietal damage and unilateral neglect
2002Co-Authors: P. VuilleumierAbstract:Perceived gaze in faces is an important social signal that may influence orienting of attention in normal observers. Would such effects of gaze still occur in patients with right parietal damage and left neglect who usually fail to attend to contralesional space? Two experiments tested for effects of perceived gaze on visual extinction. Face or shape stimuli were presented in the right, left, or both hemifields, with faces looking either straight ahead or toward the opposite field. On bilateral trials, patients extinguished a left shape much less often when a concurrent right face looked leftward rather than straight ahead. This occurred, even though gaze was not relevant to the task and processing of facial signals implied attention to a competing Ipsilesional Stimulus. By contrast, rightward gaze in faces presented on the left side had no effect on extinction, suggesting that gaze cues are not extracted without attention. Two other experiments examined effects of perceived gaze on the detection of peripheral targets. Targets appeared at one of four possible locations to the right or left of a central face looking either toward the target location, another location on the same side, the opposite side, or straight ahead. Face and gaze were not relevant to the task and not predictive of target location. Patients responded faster when the face looked toward the target on both the contralesional and Ipsilesional sides. In contralesional space, gaze allowed shifting of attention in a specific quadrant direction, but only to the first target along the scan path when there were different possible locations on the same side. By contrast, in intact Ipsilesional space, attention was selectively directed to one among different eccentric locations. Control experiments showed that symbolic arrow cues did not produce similar effects. These results indicate that even though parietal damage causes spatial neglect and impairs the representation of location o
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Perceived gaze direction in faces and spatial attention: a study in patients with parietal damage and unilateral neglect
Neuropsychologia, 2002Co-Authors: P. VuilleumierAbstract:Perceived gaze in faces is an important social signal that may influence orienting of attention in normal observers. Would such effects of gaze still occur in patients with right parietal damage and left neglect who usually fail to attend to contralesional space? Two experiments tested for effects of perceived gaze on visual extinction. Face or shape stimuli were presented in the right, left, or both hemifields, with faces looking either straight ahead or toward the opposite field. On bilateral trials, patients extinguished a left shape much less often when a concurrent right face looked leftward rather than straight ahead. This occurred, even though gaze was not relevant to the task and processing of facial signals implied attention to a competing Ipsilesional Stimulus. By contrast, rightward gaze in faces presented on the left side had no effect on extinction, suggesting that gaze cues are not extracted without attention. Two other experiments examined effects of perceived gaze on the detection of peripheral targets. Targets appeared at one of four possible locations to the right or left of a central face looking either toward the target location, another location on the same side, the opposite side, or straight ahead. Face and gaze were not relevant to the task and not predictive of target location. Patients responded faster when the face looked toward the target on both the contralesional and Ipsilesional sides. In contralesional space, gaze allowed shifting of attention in a specific quadrant direction, but only to the first target along the scan path when there were different possible locations on the same side. By contrast, in intact Ipsilesional space, attention was selectively directed to one among different eccentric locations. Control experiments showed that symbolic arrow cues did not produce similar effects. These results indicate that even though parietal damage causes spatial neglect and impairs the representation of location on the contralesional side, perceived gaze in faces can still trigger automatic shifts of attention in the contralesional direction, suggesting the existence of specific and anatomically distinct attentional mechanisms.
Anjan Chatterjee - One of the best experts on this subject based on the ideXlab platform.
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Sensory and response contributions to visual awareness in extinction
Experimental Brain Research, 2004Co-Authors: Raffaella Ricci, Anjan ChatterjeeAbstract:Brain-damaged patients may extinguish contralesional stimuli when Ipsilesional stimuli are presented simultaneously. Most theories of extinction postulate that stimuli compete for pathologically limited attentional resources with a bias to process Ipsilesional over contralesional stimuli. Implicit in this view is the idea that responses follow the outcome of an earlier competition between inputs. In the current study of two patients, we used signal detection analyses to test the hypothesis that response criteria and response modalities also contribute to visual awareness. We found that identification was more sensitive than detection in uncovering deficits of contralesional awareness. Extinction was worse with bilateral stimuli when the Ipsilesional Stimulus was identical or similar to the target than when it was dissimilar. This diminished awareness was more likely to reflect a shift towards more conservative responses rather than diminished discrimination of contralesional stimuli. By contrast, one patient was better able to discriminate contralesional stimuli when using his contralesional limb to indicate awareness of targets than when using his Ipsilesional limb. These data indicate that the nature of stimuli can modulate response criteria and the motor response can affect the sensory discriminability. Sensory discrimination and response output are not organized in a simple serial manner. Rather, input and output parameters interact in complicated ways to produce visual awareness. Visual awareness itself appears to be the outcome of two bottlenecks in processing, one having to do with sensory processing that may be covert and the other having to do with decision making, which by definition is overt. Finally, we advocate the use of signal detection analyses in studies of extinction, a method that has been surprisingly neglected in this line of research.
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Sensory and response interference by Ipsilesional stimuli in tactile extinction.
Cortex; a journal devoted to the study of the nervous system and behavior, 2000Co-Authors: Sandeep Vaishnavi, Jesse Calhoun, Anjan ChatterjeeAbstract:Extinction is thought to be due to a pathologically limited attentional capacity in which multiple stimuli cannot be processed simultaneously to conscious awareness. Patients with tactile extinction are aware of being touched on a contralesional limb, but seem unaware of similar contralesional touch if touched simultaneously on their Ipsilesional limb. The Ipsilesional Stimulus interferes and competes with the processing of the contralesional Stimulus. Most theorists assume that the Ipsilesional Stimulus affects the sensory processing of the contralesional Stimulus, although the precise functional level at which this interference occurs is not clear. We report a series of experiments using signal detection analyses to investigate tactile extinction in one patient (DC). These analyses revealed that Ipsilesional stimuli, in addition to interfering with processing of contralateral sensations, also interfere with verbal reports of those sensations. This influence on responses suggests that interference in tactile extinction can occur at a post-perceptual level, further ‘downstream’ than previously thought.
Geraint Rees - One of the best experts on this subject based on the ideXlab platform.
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unconscious activation of visual cortex in the damaged right hemisphere of a parietal patient with extinction
Brain, 2000Co-Authors: Geraint Rees, Ewa Wojciulik, Karen Clarke, Masud Husain, C D Frith, Jon DriverAbstract:Visual extinction is a sign classically associated with right parietal damage. The patient can see a single Stimulus presented in the Ipsilesional or contralesional visual field, but is characteristically unaware of the same contralesional Stimulus during simultaneous stimulation of both fields. The Ipsilesional Stimulus is said to `extinguish' the contralesional Stimulus from awareness during bilateral stimulation, perhaps due to a pathological bias in attention towards the Ipsilesional side. Recent psychophysical evidence suggests that, although extinguished stimuli are not consciously seen, they may undergo residual processing and exert implicit effects on performance. However, the neural structures mediating such residual processing for extinguished stimuli remain unknown. Here we studied the neural activity evoked by an extinguished visual Stimulus, using event-related functional MRI (fMRI), in a patient with circumscribed right inferior parietal damage and profound left-sided extinction. Monochrome objects (faces or houses) were presented in the left or right field, either unilaterally or bilaterally on each trial, with the patient indicating by button press whether he saw an object on the left, the right or on both sides. He usually saw only the right object on bilateral trials, yet the fMRI data showed activation of visual cortex contralateral to the extinguished left Stimulus on these trials (compared with right-only stimulation), in both striate and early extrastriate areas of the right hemisphere. This activity had a similar location and time-course to that resulting from a single Stimulus in the left versus right visual field. Cortical pathways involved in the normal processing of a single seen Stimulus can thus still be activated by an unseen, extinguished Stimulus after right parietal damage. Comparison of fMRI responses for faces versus houses revealed some category-specific activation for extinguished stimuli in right fusiform regions, but only at low statistical threshold. These results are discussed in terms of theoretical accounts for parietal extinction and, more generally, for the neural substrates of visual awareness.
C D Frith - One of the best experts on this subject based on the ideXlab platform.
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unconscious activation of visual cortex in the damaged right hemisphere of a parietal patient with extinction
Brain, 2000Co-Authors: Geraint Rees, Ewa Wojciulik, Karen Clarke, Masud Husain, C D Frith, Jon DriverAbstract:Visual extinction is a sign classically associated with right parietal damage. The patient can see a single Stimulus presented in the Ipsilesional or contralesional visual field, but is characteristically unaware of the same contralesional Stimulus during simultaneous stimulation of both fields. The Ipsilesional Stimulus is said to `extinguish' the contralesional Stimulus from awareness during bilateral stimulation, perhaps due to a pathological bias in attention towards the Ipsilesional side. Recent psychophysical evidence suggests that, although extinguished stimuli are not consciously seen, they may undergo residual processing and exert implicit effects on performance. However, the neural structures mediating such residual processing for extinguished stimuli remain unknown. Here we studied the neural activity evoked by an extinguished visual Stimulus, using event-related functional MRI (fMRI), in a patient with circumscribed right inferior parietal damage and profound left-sided extinction. Monochrome objects (faces or houses) were presented in the left or right field, either unilaterally or bilaterally on each trial, with the patient indicating by button press whether he saw an object on the left, the right or on both sides. He usually saw only the right object on bilateral trials, yet the fMRI data showed activation of visual cortex contralateral to the extinguished left Stimulus on these trials (compared with right-only stimulation), in both striate and early extrastriate areas of the right hemisphere. This activity had a similar location and time-course to that resulting from a single Stimulus in the left versus right visual field. Cortical pathways involved in the normal processing of a single seen Stimulus can thus still be activated by an unseen, extinguished Stimulus after right parietal damage. Comparison of fMRI responses for faces versus houses revealed some category-specific activation for extinguished stimuli in right fusiform regions, but only at low statistical threshold. These results are discussed in terms of theoretical accounts for parietal extinction and, more generally, for the neural substrates of visual awareness.
