Distinctions between manipulation and function knowledge of objects: evidence from functional magnetic resonance imaging.

A prominent account of conceptual knowledge proposes that information is distributed over visual, tactile, auditory, motor and verbal-declarative attribute domains to the degree to which these features were activated when the knowledge was acquired [D.A. Allport, Distributed memory, modular subsystems and dysphagia, In: S.K. Newman, R. Epstein (Eds.), Current perspectives in dysphagia, Churchill Livingstone, Edinburgh, 1985, pp. 32-60]. A corollary is that when drawing upon this knowledge (e.g., to answer questions), particular aspects of this distributed information is re-activated as a function of the requirements of the task at hand [L.J. Buxbaum, E.M. Saffran, Knowledge of object manipulation and object function: dissociations in apraxic and non-apraxic subjects. Brain and Language, 82 (2002) 179-199; L.J. Buxbaum, T. Veramonti, M.F. Schwartz, Function and manipulation tool knowledge in apraxia: knowing 'what for' but not 'how', Neurocase, 6 (2000) 83-97; W. Simmons, L. Barsalou, The similarity-in-topography principle: Reconciling theories of conceptual deficits, Cognitive Neuropsychology, 20 (2003) 451-486]. This account predicts that answering questions about object manipulation should activate brain regions previously identified as components of the distributed sensory-motor system involved in object use, whereas answering questions about object function (that is, the purpose that it serves) should activate regions identified as components of the systems supporting verbal-declarative features. These predictions were tested in a functional magnetic resonance imaging (fMRI) study in which 15 participants viewed picture or word pairs denoting manipulable objects and determined whether the objects are manipulated similarly (M condition) or serve the same function (F condition). Significantly greater and more extensive activations in the left inferior parietal lobe bordering the intraparietal sulcus were seen in the M condition with pictures and, to a lesser degree, words. These findings are consistent with the known role of this region in skilled object use [K.M. Heilman, L.J. Gonzalez Rothi, Apraxia, In: K.M. Heilman, E. Valenstein (Eds.), Clinical Neuropsychology, Oxford University Press, New York, 1993, pp. 141-150] as well as previous fMRI results [M. Kellenbach, M. Brett, K. Patterson, Actions speak louder than functions: the importance of manipulability and action in tool representation, Journal of Cognitive Neuroscience, 15 (2003) 30-46] and behavioral findings in brain-lesion patients [L.J. Buxbaum, E.M. Saffran, Knowledge of object manipulation and object function: dissociations in apraxic and non-apraxic subjects, Brain and Language, 82 (2002) 179-199]. No brain regions were significantly more activated in the F than M condition. These data suggest that brain regions specialized for sensory-motor function are a critical component of distributed representations of manipulable objects.

Contrasting effects of phonological priming in aphasic word production.

Two fluent aphasics, IG and GL, performed a phonological priming task in which they repeated an auditory prime then named a target picture. The two patients both had selective deficits in word production: they were at or near ceiling on lexical comprehension tasks, but were significantly impaired in picture naming. IG's naming errors included both semantic and phonemic paraphasias, as well as failures to respond, whereas GL's errors were mainly phonemic and formal paraphasias. The two patients responded very differently to phonological priming: IG's naming was facilitated (both accuracy and speed) only by begin-related primes (e.g. ferry-feather), whereas GL benefited significantly only from end-related primes (e.g. brother-feather), showing no more than a facilitatory trend with begin-related primes. We interpret these results within a two-stage model of word production, in which begin-related and end-related primes are said to operate at different stages. We then discuss implications for models of normal and aphasic word production in general and particularly with respect to sequential aspects of the phonological encoding process.

Differences in word associations to pictures and words.

Normal subjects were asked to produce the "first word that comes to mind" in response to pictures or words that differed with respect to manipulability and animacy. In separate analyses across subjects and items, normal subjects produced a significantly higher proportion of action words (that is, verbs) to pictures as compared to words, to manipulable as compared to non-manipulable stimuli and to inanimate as compared to animate stimuli. The largest proportion of action words was elicited by pictures of non-living, manipulable objects. Furthermore, associates to words matched standard word associates significantly more often than those elicited by pictures. These data suggest that pictures and words initially contact different forms of conceptual information and are consistent with an account of semantic organization that assumes that information is distributed across different domains reflecting the mode of acquisition of that knowledge.

Knowledge of the human body: a distinct semantic domain.

BACKGROUND: Patients with selective deficits in the naming and comprehension of animals, plants, and artifacts have been reported. These descriptions of specific semantic category deficits have contributed substantially to the understanding of the architecture of semantic representations. OBJECTIVE: This study sought to further understanding of the organization of the semantic system by demonstrating that another semantic category, knowledge of the human body, may be selectively preserved. METHODS: The performance of a patient with semantic dementia was compared with the performance of healthy controls on a variety of tasks assessing distinct types of body representations, including the body schema, body image, and body structural description. RESULTS: Despite substantial deficits on tasks involving language and knowledge of the world generally, the patient performed normally on all tests of body knowledge except body part naming; even in this naming task, however, her performance with body parts was significantly better than on artifacts. CONCLUSIONS: The demonstration that body knowledge may be preserved despite substantial semantic deficits involving other types of semantic information argues that body knowledge is a distinct and dissociable semantic category. These data are interpreted as support for a model of semantics that proposes that knowledge is distributed across different cortical regions reflecting the manner in which the information was acquired.

Knowledge of object manipulation and object function: dissociations in apraxic and nonapraxic subjects.

An influential account of selective semantic deficits posits that visual features are heavily weighted in the representations of animals, whereas information about function is central in the representations of tools (e.g., Warrington & Shallice, 1984 ). An alternative account proposes that information about all types of objects-animate and inanimate alike-is represented in a distributed semantic architecture by verbal-propositional, tactile, visual, and proprioceptive-motor nodes, reflecting the degree to which these systems were activated when the knowledge was acquired (e.g., Allport, 1985 ). We studied a group of left hemisphere chronic stroke patients, some of whom were apraxic, with measures of declarative tool and animal knowledge, body part knowledge, and function and manipulation knowledge of artifacts. Apraxic (n=7) and nonapraxic (n=6) subjects demonstrated a double dissociation of performance on tests of tool and animal knowledge, suggesting that the apraxic group was not simply more severely impaired overall. Apraxics were relatively impaired in manipulation knowledge, whereas nonapraxics tended to be relatively impaired in function knowledge. Apraxics were also more impaired with body parts than nonapraxics. The association of gestural praxis, tool knowledge, body part knowledge, and manipulation knowledge suggests a coherent basis for the organization of semantic artifact knowledge in frontoparietal cortical regions specialized for sensorimotor functions, and thus provides support for the distributed architecture account of the semantic system.

IMPLICIT VS. LETTER-BY-LETTER READING IN PURE ALEXIA: A TALE OF TWO SYSTEMS.

Recent studies of pure alexia present a contradictory picture. Despite evidence of impaired letter identification in letter-by-letter readers, some patients are able to carry out lexical decision and other tasks under conditions of rapid presentation, although they are seldom able to identify these stim uli explicitly. We review evidence for both facets of pure alexic performance and offer an accountof this pattern in terms ofright-and left-hemisphere reading mechanisms. Specifically, we suggest that the right hemisphere supports performance in covert reading tasks, and that letter-by-letter reading is the product of the left hemisphere, operating on information transmitted from the right.