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Bartels, A., & Zeki, S. (2000). The architecture of the colour centre in the human visual brain: new results and a review. European Journal of Neuroscience, 12(1), 172- 190.

We have used the technique of functional magnetic resonance imaging (fMRI) and a variety of colour paradigms to activate the human brain regions selective for colour. We show here that the region defined previously [Lueck et al. (1989) Nature, 340, 386-389; Zeki et al. (1991) J. Neurosci., 11, 641-649; McKeefry & Zeki (1997) Brain, 120, 2229-2242] as the human colour centre consists of two subdivisions, a posterior one, which we call V4 and an anterior one, which we refer to as V4 alpha, the two together being part of the V4-complex. The posterior area is retinotopically organized while the anterior is not. We discuss our new findings in the context of previous studies of the cortical colour processing system in humans and monkeys. Our new insight into the organization of the colour centre in the human brain may also account for the variability in both severity and degree of recovery from lesions producing cerebral colour blindness (achromatopsia).


Büchel, C, Price, C, Frackowiak, RSJ & Friston, K (1998) Different activation patterns in the visual cortex of late and congenitally blind subjects. Brain, Vol.121, No.Pt3, Pp.409-419.

A key issue in developmental neuroscience is the role of activitydependent mechanisms in the epigenetic induction of functional organization in visual cortex. Ocular blindness and ensuing visual deprivation is one of the rare models available for the investigation of experience-dependent cortical reorganization in man. In a PET study we demonstrate that congenitally blind subjects show taskspecific activation of extrastriate visual areas and parietal association areas during Braille reading, compared with auditory word processing. In contrast, blind subjects who lost their sight after puberty show additional activation in the primary visual cortex with the same tasks. Studies in blind-raised monkeys show that crossmodal responses in extrastriate areas can be elicited by somatosensory stimulation. This is consistent with the crossmodal extrastriate activations elicited by tactile processing in our congenitally blind subjects. Since primary visual cortex does nor show crossmodal responses in primate studies, the differential activation in late and congenitally blind subjects highlights the possibility of reciprocal activation by visual imagery in subjects with early visual experience.

Carlsson, K., Petrovic, P., Skare, S., Petersson, K. M., & Ingvar, M. (2000). Tickling expectations: Neural processing in anticipation of a sensory stimulus. Journal of Cognitive Neuroscience, 12(4), 691-703.

Predictions of the near future can optimize the accuracy and speed of sensory processing as well as of behavioral responses. Previous experience and contextual cues are essential elements in the generation of a subjective prediction. Using a blocked fMRI paradigm, we investigated the pattern of neural activation in anticipation of a sensory stimulus and during the processing of the somatosensory stimulus itself. Tickling was chosen as the somatosensory stimulus rather than simple touch in order to increase the probability to get a high degree of anticipation. The location and nature of the stimulus were well defined to the subject. The state of anticipation was initiated by attributing an uncertainty regarding the time of stimulus onset. The network of activation and deactivation during anticipation of the expected stimulus was similar to that engaged during the actual sensory stimulation. The areas that were activated during both states included the contralateral primary sensory cortex, bilateral areas in the inferior parietal lobules, the putative area SII, the right anterior cingulate cortex and areas in the right prefrontal cortex. Similarly, common decreases were observed in areas of sensorimotor cortex located outside the area representing the target of stimulus, i.e., areas that process information which is irrelevant to the attended process. The overlapping pattern of change, during the somatosensory stimulation and the anticipation, furthers the idea that predictions are subserved by a neuronal network similar to that which subserves the processing of actual sensory input. Moreover, this study indicates that activation of primary somatosensory cortex can be obtained without intra-modal sensory input. These findings suggest that anticipation may invoke a tonic top-down regulation of neural activity.

Cowey, A., & Vaina, L. M. (2000). Blindness to form from motion despite intact static form perception and motion detection. Neuropsychologia, 38(5), 566-578.

We studied the motion perception, including form and meaning generated by motion, in a hemianopic patient who also bad visual perceptual impairments in her seeing hemifeld as a result of a lesion in ventral extrastriate cortex. She was unable to recognise 2- or 3-dimensional forms, and ei en borders, generated by motion alone, failed to recognise mimed actions err the Johannson 'biological motion' display, and ceased to recognise people well-known to her when they moved. I-Icr performance with static displays, although impaired, could not explain her inability to perceive shape or derive meaning from moving displays. Unlike a motion-blind patient, she can still see and describe the motion, with the exception of second-order motion, but not what it creates or represents. (C) 2000 Elsevier Science Ltd. All rights reserved.

Dehaene-Lambertz, G. (2000). Cerebral specialization for speech and non-speech stimuli in infants. Journal of Cognitive Neuroscience, 12(3), 449-460.

Early cerebral specialization and lateralization for auditory processing in 4-month-old infants was studied by recording high-density evoked potentials to acoustical and phonetic changes in a series of repeated stimuli (either tones or syllables). Mismatch responses to these stimuli exhibit a distinct topography suggesting that different neural networks within the temporal lobe are involved in the perception and representation of the different features of an auditory stimulus. These data confirm that specialized modules are present within the auditory cortex very early in development. However, both for syllables and continuous tones, higher voltages were recorded over the left hemisphere than over the right with no significant interaction of hemisphere by type of stimuli. This suggests that there is no greater left hemisphere involvement in phonetic processing than in acoustic processing during the first months of life.

Engelien, A., Huber, W., Silbersweig, D., Stern, E., Frith, C. D., Doring, W., Thron, A., & Frackowiak, R. S. J. (2000). The neural correlates of 'deaf-hearing' in man - Conscious sensory awareness enabled by attentional modulation. Brain, 123, 532-545.

Attentional modulation of normal sensory processing has a two- fold impact on human brain activity: activation of a network of localized brain regions is associated with paying attention, and activation of specific sensory regions is enhanced relative to passive stimulation. The mechanisms underlying attentional modulation of perception in patients with lesions of sensory cortices are less well understood, Here we report a unique patient suffering from extensive bilateral destruction of the auditory cortices (including the primary auditory fields) who demonstrated conscious perception of the onset and offset of sounds only when selectively attending to the auditory modality. This is the first description of such an attentively modulated 'deaf-hearing' phenomenon and its neural correlates, using (H2O)-O-15-PET, Increases in cerebral blood flow associated with conscious awareness of sound that was achieved by listening attentively (compared with identical auditory stimulation presented when the patient was inattentive) were found bilaterally in the lateral (pre)frontal cortices, the spared middle temporal cortices and the cerebellar hemispheres. We conclude that conscious awareness of sounds may be achieved in the absence of the primary auditory cortex, and that selective, 'top-down' attention, associated with prefrontal systems, exerts a crucial modulatory effect on auditory perception within the remaining auditory system.

Ffytche, D. H., Howseman, A., Edwards, R., Sandeman, D. R., & Zeki, S. (2000). Human area V5 and motion in the ipsilateral visual field. European Journal of Neuroscience, 12(8), 3015-3025.

We have studied area V5 of the human brain with visually-evoked potential (VEP) and functional magnetic resonance imaging (fMRI) methods, using hemifield motion stimuli. Our results confirmed the presence of an ipsilateral field representation in V5 and found: (i) a delay in the ipsilateral response in V5, irrespective of the hemifield stimulated; (ii) a longer ipsilateral delay for left hemifield than for right hemifield stimulation; and (iii) in a patient with a section of the splenium, an absent ipsilateral response for right but not left hemifield stimulation. Together with neurophysiological and anatomical evidence in the monkey, our non-invasive spatial and temporal imaging studies in man reveal that ipsilateral V5 is activated by motion signals transferred from contralateral V5. The asymmetry of ipsilateral delay in normal subjects and the asymmetrical loss of ipsilateral response following splenial section imply that signals related to visual motion are transferred from one V5 to the other through two segregated pathways.

Florence, S. L., Hackett, T. A., & Strata, F. (2000). Thalamic and cortical contributions to neural plasticity after limb amputation. Journal of Neurophysiology, 83(5), 3154-3159.

Little is known about the substrates for the large-scale shifts in the cortical representation produced by limb amputation. Subcortical changes likely contribute to the cortical remodeling, yet there is little data regarding the extent and pattern of reorganization in thalamus after such a massive deafferentation. Moreover, the relationship between changes in thalamus and in cortex after injuries of this nature is virtually unexplored. Multiunit microelectrode maps were made in the somatosensory thalamus and cortex of two monkeys that had long-standing, accidental forelimb amputations. In the deprived portion of the ventroposterior nucleus of the thalamus (VP), where stimulation to the hand would normally activate neurons, new receptive fields had emerged. At some recording sites within the deprived zone of VP, neurons responded to stimulation of the remaining stump of the arm and at other sites neurons responded to stimulation of both the stump and the face. This same overall pattern of reorganization was present in the deprived hand representation of cortical area 3b. Thus thalamic changes produced by limb amputation appear to be an important substrate of cortical reorganization. However, a decrease in the frequency of abnormal stump/face fields in area 3b compared with VP and a reduction in the size of the fields suggests that cortical mechanisms of plasticity may refine the information relayed from thalamus.

Iacoboni, M., Woods, R. P., Brass, M., Bekkering, H., Mazziotta, J. C., & Rizzolatti, G. (1999). Cortical mechanisms of human imitation. Science, 286(5449), 2526- 2528.

How does imitation occur? How can the motor plans necessary for imitating an action derive from the observation of that: action? Imitation may be based on a mechanism directly matching the observed action onto an internal motor representation of that action ("direct matching hypothesis"). To test this hypothesis, normal human participants were asked to observe and imitate a finger movement and to perform the same movement after spatial or symbolic cues. Brain activity was measured with functional magnetic resonance imaging. If the direct matching hypothesis is correct, there should be areas that become active during finger movement; regardless of how it is evoked, and their activation should increase when the same movement is elicited by the observation of an identical movement made by another individual. Two areas with these properties were found in the left; inferior frontal cortex (opercular region) and the rostral-most region of the right superior parietal lobule.

Knecht, S., Deppe, M., Drager, B., Bobe, L., Lohmann, H., Ringelstein, E. B., & Henningsen, H. (2000). Language lateralization in healthy right-handers. Brain, 123, 74-81.

Our knowledge about the variability of cerebral language lateralization is derived from studies of patients: with brain lesions and thus possible secondary reorganization of cerebral functions. In healthy right-handed subjects 'atypical', i.e, right hemisphere language dominance, has generally been assumed to be exceedingly rare. To test this assumption we measured language lateralization in 188 healthy subjects with moderate and strong right-handedness (59% females) by a new non- invasive, quantitative technique previously validated by direct comparison with the intracarotid amobarbital procedure, During a word generation task the averaged hemispheric perfusion differences within the territories of the middle cerebral arteries were determined. (i) The natural distribution of language lateralization was found to occur along a bimodal continuum. (ii) Lateralization was equivalent in men and women,. (iii) Right hemisphere dominance was found in 7.5% of subjects, These findings indicate that atypical language dominance in healthy right-handed subjects of either sex is considerably more common than previously suspected.

[not in handout, see intranet]

Kreiman, G.,Koch, C. & Fried, I. (2000) Category-specific visual responses of single neurons in the human medial temporal lobe Nature Neuroscience September Volume 3 Number 9 pp 946 - 953

  • Recorded from 427 single neurons in the human hippocampus, entorhinal cortex and amygdala,

  • found a remarkable degree of category-specific firing of individual neurons on a trial-by-trial basis.

  • Of the recorded neurons, 14% responded selectively to visual stimuli from different categories, including faces, natural scenes and houses, famous people and animals.

  • Based on the firing rate of individual neurons, stimulus category could be predicted with a mean probability of error of 0.24. In the hippocampus, the proportion of neurons responding to spatial layouts was greater than to other categories.

  • data provide direct support for the role of human medial temporal regions in the representation of different categories of visual stimuli.
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Kujala, T., Alho, K., & Naatanen, R. (2000). Cross-modal reorganization of human cortical functions. Trends in Neurosciences, 23(3), 115-120.

Recent technological development has opened fascinating opportunities in research on cognitive functions of the human brain. For example, cortical representations of sensory functions and their reorganization, which have been studied thoroughly in animals, are far better understood in humans now than they were only a decade ago, Hemodynamic and electromagnetic studies have demonstrated that a modality- specific brain area that is totally deprived of its normal sensory input becomes responsive to stimulation of other modalities,The functional significance of this crossmodal activation was recently indicated by,for example, studies showing that the occipital cortex of the blind is activated by sound changes, when the task is to detect these changes, Moreover, transcranial magnetic stimulation applied to the occipital cortex of blind individuals results in distortions and omissions of letters in Braille text being read by the subject, Contrary to prevailing views, crossmodal neural reorganization might, as shown by recent results, take place even in the mature human brain.

Leclerc, C., Saint-Amour, D., Lavoie, M. E., Lassonde, M., & Lepore, F. (2000). Brain functional reorganization in early blind humans revealed by auditory event-related potentials. Neuroreport, 11(3), 545-550.

Visually challenged individuals often compensate for their handicap by developing supra-normal abilities in their remaining sensory systems. Here, we examined the scalp distribution of components NI and P3 of auditory evoked potentials during a sound localization task in four totally blind subjects who had previously shown better performance than sighted subjects. Both NI and P3 waves peaked at their usual positions while blind acid sighted individuals performed the task. However, in blind subjects these two components were also found to be robust over occipital regions while in sighted individuals this pattern was not seen. We conclude that deafferented posterior visual areas in blind individuals are recruited to carry:out auditory functions, enabling these individuals to compensate for their lack of vision. NeuroReport 11:545-550 (C) 2000 Lippincott Williams & Wilkins.

Lee, H. W., Hong, S. B., Seo, D. W., Tae, W. S., & Hong, S. C. (2000). Mapping of functional organization in human visual cortex - Electrical cortical stimulation. Neurology, 54(4), 849-854.


Lee, H. W., Hong, S. B., Seo, D. W., Tae, W. S., & Hong, S. C. (2000). Mapping of functional organization in human visual cortex - Electrical cortical stimulation. Neurology, 54(4), 849-854.

Objectives: To investigate the pattern of functional organization in the human visual cortex through electrical cortical stimulation. Methods: Electrical cortical stimulation was applied to the occipital cortex and adjacent cortices using subdural grid electrodes in 23 epilepsy patients. Diverse visual responses were recorded. These responses were divided into different categories according to the specific response modalities, such as form, color, and motion. Form visual responses were further subdivided into simple, intermediate, and complex responses. The cortical localization of subdural electrodes was identified using MRI-CT coregistration, The cortical distribution of different visual responses was projected into three-dimensional surface renderings of the brain. The distribution and frequency of subdural electrodes showing different visual responses were quantified by calculating the percentage of the number of electrodes showing one specific type of visual response at the corresponding anatomic region to the total number of electrodes in all brain regions that produced the same response. Results: Simple form responses mere obtained mostly at the occipital pole and the inferior occipital gyrus (47.4%) and the striate cortex (42.4%). Intermediate form responses occurred mainly on the peristriate cortex (52.5%) and the lateral occipital (28.0%) and fusiform gyri (19.5%). Complex forms were produced by stimulation of the basal temporo-occipital region (57.6%) and the lateral temporal or lateral temporo-occipital junctional region (42.4%), Color responses occurred on the basal occipital area, mostly at the fusiform (40.0%) and lingual gyri (36.0%). Moving sensations were evoked by stimulation of the basal temporo-occipital (28.4%) and the mesial parietooccipital or temporo- parieto- occipital junctional regions (23.9%). Conclusions: Different modalities of vision, such as form, color, and moving sensation, appeared to be distributed and organized in different areas of the human visual cortex.


Moore, C. E. G., & Schady, W. (2000). Investigation of the functional correlates of reorganization within the human somatosensory cortex. Brain, 123, 1883-1895.

Much work in animals and humans has demonstrated the existence of changes in topographic organization within the somatosensory cortex (SSC) after amputation or nerve injury. Afferent inputs from one area of skin are able to activate novel areas of cortex after amputation of an adjacent body part. We have investigated the functional consequences of this reorganization in a group of patients with nerve injury. Using the microneurographic technique of intraneural microstimulation (INMS) we stimulated groups of nerve fibres, within individual fascicles proximal to the nerve transection, with small electrical pulses. This enabled us to activate the deafferented cortex that had presumably undergone remodelling and study the conscious percepts described by the subjects. In 39 fascicles from 10 subjects, we found that the sensations evoked on INMS were no different from those reported previously by subjects with intact nerves. This finding suggests that such reorganization within the SSC has little effect on the function of deafferented cortical neurones or subcortical relay stations. In a separate set of experiments, INMS was performed in 16 nerve fascicles from an adjacent non-injured nerve or uninjured fascicle within a partially injured nerve. The sensations evoked by INMS in these experiments were also comparable to those obtained in normal subjects. This indicates that the expanded cortical representation of adjacent non- anaesthetic skin does not influence the cortical processing of afferent information. Taken together, these findings lead us to question the notion that reorganization of connections within the somatosensory cortex equates to a change in function. Whilst it may be advantageous that the human brain is not 'hard-wired', neurophysiological proof of functional plasticity in the adult somatosensory system as a result of deafferentation is elusive.

Moutoussis, K., & Zeki, S. (2000). A psychophysical dissection of the brain sites involved in color-generating comparisons. Proceedings of the National Academy of Sciences of the United States of America, 97(14), 8069-8074.

We have used simple psychophysical methods to determine the sites of color-generating mechanisms in the brain. In our first experiment, subjects viewed an abstract multicolored "Mondrian" display through one eye and an isolated patch from the display through the other. With normal binocular/monocular viewing, the patch has a different color when viewed on its own (void mode) or as part of the Mondrian display (natural mode) [Land, E. H. (1974) Proc. R, Inst. G. B. 49, 23-58]. When the two stimuli were viewed dichoptically, with the patch occupying the position that it would occupy in the Mondrian complex under normal viewing, the patch always appeared in its void color. In a second experiment, when subjects viewed multicolored displays through a different narrowband filter placed over each eye, the information from the two eyes was combined to result in new colors, which were not seen through either of the two eyes alone. Taken together, these results dissect color-generating mechanisms into two stages, located at different sites of the brain: The first occurs before the appearance of binocular neurons in the cortex and compares wavelength information across space, whereas the second occurs after the convergence of the input from the two eyes and synthetically combines the results of the first.

Musso, M., Weiller, C., Kiebel, S., Muller, S. P., Bulau, P., & Rijntjes, M. (1999). Training-induced brain plasticity in aphasia. Brain, 122, 1781-1790.

It has long been a matter of debate whether recovery from aphasia after left perisylvian lesions is mediated by the preserved left hemispheric language zones or by the homologous right hemisphere regions. Using PET, we investigated the short- term changes in the cortical network involved in language comprehension during recovery from aphasia. In 12 consecutive measurements of regional cerebral blood flow (rCBF), four patients with Wernicke's aphasia, caused by a posterior left middle cerebral artery infarction, were tested with a language comprehension task, Comprehension was estimated directly after each scan with a modified version of the Token Test, In the interval between the scans, the patients participated in brief, intense language comprehension training. A significant improvement in performance was observed in all patients. We correlated changes in blood flow measured during the language comprehension task with the scores achieved in the Token Test. The regions which best correlated with the training-induced improvement in verbal comprehension were the posterior part of the right superior temporal gyrus and the left precuneus. This study supports the role of the right hemisphere in recovery from aphasia and demonstrates that the improvement in auditory comprehension induced by specific training is associated with functional brain reorganization.

Poldrack, R. A. (2000). Imaging brain plasticity: Conceptual and methodological issues - A theoretical review. Neuroimage, 12(1), 1-13.

The neural plasticity associated with learning and development is increasingly being studied using functional neuroimaging methods such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). In this paper I outline a set of conceptual and methodological issues that are particularly relevant for the study of neural plasticity. A number of confounds, related to changes in performance and the inherently temporal nature of learning and development, must be addressed when imaging plasticity. The interpretation of changes in imaging signals is greatly underdetermined, suggesting that hypothesis-driven research approaches may be most fruitful. Finally, I argue that the imaging of learning- related and developmental plasticity can enhance the ability of functional neuroimaging to identify and characterize the underlying neural basis of cognition. (C) 2000 Academic Press.


Sekiyama, K., Miyauchi, S., Imaruoka, T., Egusa, H., & Tashiro, T. (2000). Body image as a visuomotor transformation device revealed in adaptation to reversed vision. Nature, 407(6802), 374-377.

People adapt with remarkable flexibility to reversal of the visual field caused by prism spectacles(1,2). With sufficient time, this adaptation restores visually guided behaviour and perceptual harmony between the visible and tactile worlds(1-3). Although it has been suggested that seeing one's own body is crucial for adaptation(1,2), the underlying mechanisms are unclear. Here we show that a new representation of visuomotor mapping with respect to the hands emerges in a month during adaptation to reversed vision. The subjects become bi- perceptual(3-5), or able to use both new and old representations. In a visual task designed to assess the new hand representation, subjects identified visually presented hands as left or right by matching the picture to the representation of their own hands. Functional magnetic resonance imaging showed brain activity in the left posterior frontal cortex (Broca's area) that was unique to the new hand representations of both hands, together with activation in the intraparietal sulcus and prefrontal cortex. The emergence of the new hand representation coincided with the adaptation of perceived location of visible objects in space. These results suggest that the hand representation operates as a visuomotor transformation device that provides an arm-centred frame of reference(6) for space perception.

Skiera, G., Petersen, D., Skalej, M., & Fahle, M. (2000). Correlates of figure-ground segregation in fMRI. Vision Research, 40(15), 2047-2056.

We investigated which correlates of figure-ground-segregation can be detected by means of functional magnetic resonance imaging (fMRI). Five subjects were scanned with a Siemens Vision 1.5 T system. Motion, colour, and luminance-defined checkerboards were presented with alternating control conditions containing one of the two features of the checkerboard. We find a segregation- specific activation in V1 for all subjects and all stimuli and conclude that neural mechanisms exist as early as in the primary visual cortex that are sensitive to figure-ground segregation. (C) 2000 Elsevier Science Ltd. All rights reserved.


Weiss, T., Miltner, W. H. R., Huonker, R., Friedel, R., Schmidt, I., & Taub, E. (2000). Rapid functional plasticity of the somatosensory cortex after finger amputation. Experimental Brain Research, 134(2), 199-203.

Recent research indicates that areas of the primary somatosensory (SI) and primary motor cortex show massive cortical reorganization after amputation of the upper arm, forearm or fingers. Most of these studies were carried out months or several years after amputation. In the present study, we describe cortical reorganization of areas in the SI of a patient who underwent amputation of the traumatized middle and ring fingers of his right hand 10 days before cortical magnetic source imaging data were obtained. Somatosensory-evoked;ed magnetic fields (SEF) to mechanical stimuli to the finger tips were recorded and single moving dipoles were calculated using a realistic volume conductor model. Results reveal that the dipoles representing the second and fifth fingers of the affected hand were closer together than the comparable dipoles of the unaffected hand. Our findings demonstrate that neural cell assemblies in SI which formerly represented the right middle and ring fingers of this amputee became reorganized and invaded by neighbouring cell assemblies of the index and little finger of the same hand. These results indicate that functional plasticity occurs within a period of 10 days after amputation.


Zeki, S., & Bartels, A. (1999). The clinical and functional measurement of cortical (in)activity in the visual brain, with special reference to the two subdivisions (V4 and V4 alpha) of the human colour centre. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences, 354(1387), 1371-1382.

We argue below that, at least in studying the visual brain, the old and simple methods of detailed clinical assessment and perimetric measurement still yield important insights into the organization of the visual brain as a whole, as well as the organization of the individual areas within it. To demonstrate our point, we rely especially on the motion and colour systems, emphasizing in particular how clinical observations predicted an important feature of the organization of the colour centre in the human brain. With the use of data from functional magnetic resonance imaging analysed by statistical parametric mapping and independent component analysis, we show that the colour centre is composed of two subdivisions, V4 and V4 alpha, the two together constituting the V4 complex of the human brain. These two subdivisions are intimately linked anatomically and act cooperatively The new evidence about the architecture of the colour centre might help to explain why the syndrome, cerebral achromatopsia, produced by lesions in it is so variable.


Zeki, S., Aglioti, S., McKeefry, D., & Berlucchi, G. (1999). The neurological basis of conscious color perception in a blind patient. Proceedings of the National Academy of Sciences of the United States of America, 96(24), 14124-14129.

We have studied patient PB, who, after an electric shock that led to vascular insufficiency, became virtually blind, although he retained a capacity to see colors consciously. For our psychophysical studies, we used a simplified Version of the Land experiments [Land, E.(1974) Proc. R. Inst G. B. 47, 23-58] to learn whether color constancy mechanisms are intact in him, which amounts to teaming whether he can assign a constant color to a surface in spite of changes in the precise wavelength composition of the light reflected from that surface. We supplemented our psychophysical studies with imaging ones, using functional magnetic resonance, to learn something about the location of areas that are active in his brain when he perceives colors. The psychophysical results suggested that color constancy mechanisms are severely defective in PB and that his color vision is wavelength-based. The imaging results showed that, when he viewed and recognized colors, significant in creases in activity were restricted mainly to V1-V2. We conclude that a partly defective color system operating on its own in a severely damaged brain is able to mediate a conscious experience of color in the virtually total absence of other visual abilities.  

Start | basic neuroanat. | reading | zeki extracts | table of links | Refs by topic | Journals