Cognitive and Neural Mechanisms Underlying Visual and Semantic Processing: Implications from Optic Aphasia

We report detailed analyses of the performance of a patient, DHY, who as a consequence of strokes in the left occipital lobe and the periventricular white matter in the region of the spleniuni, showed severely impaired naming of visual stimuli despite spared recognition of visual stimuli and spared naming in other modalities. This pattern of performancelabeled optic aphasiahas been previously interpreted as support for the hypothesis that there are independent semantic systems, either a visual and a verbal semantic store (Beauvois, 1982; Lhermitte & Beauvois, 1973) or a right hemisphere and a left hemisphere semantic system (Coslett & Saffran, 1989, l092), which are disconnected in these patients. We provide evidence that DHY shows precisely the types of performance across a variety of verbal and visual tasks that have been used to support these claims of separate semantic systems: (1) good performance in naming to definition and naming objects presented for tactile exploration (which has been interpreted as evidence of spared verbal or left hemisphere semantic processing), and (2) good performance on various semantic tasks that do not require naming (which has been interpreted as access to spared visual or right hemisphere semantic processing). Nevertheless, when nonverbal semantic tasks were modified such that they required access to more detailed semantic information for accurate performance, DHY was Par less accurate, indicating that she did not access complete semantic information about objects in the visual modality. We argue that these data undermine the claim that cases of optic aphasia can be explained only by proposing multiple semantic systems. We propose an alternative account for this pattern of performance, within a model of visual object naming that specifies a single, modality-independent semantic system. We show that the performance of DHY and other optic aphasic patients can be explained by proposing a deficit in accessing a complete, modality-independent, lexical-semantic representation from an intact stored, structural description of the object. We discuss the implications of these conclusions for claims about the neuroanatomical correlates of semantic and visual object processing.

[1]  Harry A. Whitaker,et al.  Brain and Language , 1994 .

[2]  D. Grossi,et al.  Impaired drawing from memory in a visual agnosic patient , 1992, Brain and Cognition.

[3]  T. Shallice,et al.  Perseverative and Semantic Influences on Visual Object Naming Errors in Optic Aphasia: A Connectionist Account , 1993, Journal of Cognitive Neuroscience.

[4]  Ruth Campbell,et al.  Optic aphasia with spared action naming: A description and possible loci of impairment , 1992, Neuropsychologia.

[5]  H. Coslett,et al.  Preserved object recognition and reading comprehension in optic aphasia. , 1989, Brain : a journal of neurology.

[6]  K. Heilman,et al.  Lexical agraphia. Further support for the two-system hypothesis of linguistic agraphia. , 1984, Brain : a journal of neurology.

[7]  A. Benton,et al.  Dissociation of visual and tactile naming in amnesic aphasia , 1966, Neurology.

[8]  J. A. Fodor,et al.  Against definitions , 1980, Cognition.

[9]  J. Sergent,et al.  Positron emission tomography study of letter and object processing: empirical findings and methodological considerations. , 1992, Cerebral cortex.

[10]  John Hart,et al.  Delineation of single‐word semantic comprehension deficits in aphasia, with anatomical correlation , 1990, Annals of neurology.

[11]  T. Shallice Specialisation within the semantic system , 1988 .

[12]  Glyn W. Humphreys,et al.  Semantic systems or system? Neuropsychological evidence re-examined , 1988 .

[13]  A. Kertesz The Western Aphasia Battery , 1982 .

[14]  M. Beauvois,et al.  Optic aphasia for colours and colour agnosia: A distinction between visual and visuo-verbal impairments in the processing of colours , 1985 .

[15]  A. Caramazza,et al.  Where Do Semantic Errors Come From? , 1990, Cortex.

[16]  M. J. Riddoch,et al.  Visual object processing in optic aphasia: a case of semantic access agnosia , 1987 .

[17]  F. Lhermitte,et al.  A visual-speech disconnexion syndrome. Report of a case with optic aphasia, agnosic alexia and colour agnosia. , 1973, Brain : a journal of neurology.

[18]  J. Mcglone,et al.  Speech comprehension after unilateral injection of sodium amytal , 1984, Brain and Language.

[19]  G. Miller,et al.  Language and Perception , 1976 .

[20]  M. Beauvois,et al.  Optic aphasia: a process of interaction between vision and language. , 1982, Philosophical transactions of the Royal Society of London. Series B, Biological sciences.

[21]  Karl J. Friston,et al.  Distribution of cortical neural networks involved in word comprehension and word retrieval. , 1991, Brain : a journal of neurology.

[22]  Optic aphasia, optic apraxia and loss of dreaming , 1997 .

[23]  R. Sperry,et al.  Language after section of the cerebral commissures. , 1967, Brain : a journal of neurology.

[24]  Harvey S. Levin,et al.  Visual agnosia contrasted with visual-verbal disconnection , 1985, Neuropsychologia.

[25]  E K Warrington,et al.  Selective impairment of memory and visual perception in splenial tumours. , 1991, Brain : a journal of neurology.

[26]  G. Humphreys,et al.  Visual object processing in optic aphasia: a case of semantic access agnosia , 1987 .

[27]  H. Coslett,et al.  Optic aphasia and the right hemisphere: A replication and extension , 1992, Brain and Language.

[28]  J. G. Snodgrass,et al.  A standardized set of 260 pictures: norms for name agreement, image agreement, familiarity, and visual complexity. , 1980, Journal of experimental psychology. Human learning and memory.

[29]  Alfonso Caramazza,et al.  Selective impairment of semantics in lexical processing , 1990 .

[30]  M. Posner,et al.  Positron Emission Tomographic Studies of the Processing of Singe Words , 1989, Journal of Cognitive Neuroscience.

[31]  Ann M. Peters,et al.  Phonological encoding and ideographic reading by the disconnected right hemisphere: Two case studies , 1981, Brain and Language.

[32]  George F. McCormick,et al.  Visual anomia , 1983, Neurology.

[33]  Leslie G. Ungerleider,et al.  Dissociation of object and spatial visual processing pathways in human extrastriate cortex. , 1991, Proceedings of the National Academy of Sciences of the United States of America.