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R A McCarthy

Publications and source records attributed to R A McCarthy.

At least 19 recordsLinked to original sources
PubMed1997

The neuropsychology of object constancy.

There have been several proposals for the mechanism by which we are able to recognize an object across a number of viewpoints. Viewpoint-dependent accounts suggest that recognition may be based on an incremental transformation (e.g., mental rotation) strategy, while a variety of viewpoint-independent mechanisms for object recognition have also been proposed. Recent research in neurobiology, based on the two cortical visual systems account, suggest that the processes of viewpoint-dependent and viewpoint-independent object recognition may rely on separate anatomical regions, and that brain lesions may leave patients with selective access to particular types of representation. Evidence from a variety of neuropsychological disorders are reviewed to support the position that viewpoint-independent object recognition depends upon the integrity of occipitotemporal structures. In addition, it is suggested that viewpoint-dependent processes (perhaps depending on occipitoparietal structures) may supplement this primary system under nonoptimal circumstances.

Attention↗
PubMed1996

When is a view unusual? A single case study of orientation-dependent visual agnosia.

Several hypotheses have been proposed to explain why some neurological patients fail to recognise objects from unusual views: that it results from difficulty identifying an object's principal axis when it is foreshortened, identifying an object when landmark features are occluded, or an inability to rotate mental images. It was possible to test these hypotheses by examining the recognition abilities of a single case (A.S.), by using stimuli that were "unusual" only because of picture-plane misorientation. A.S. showed a recognition deficit in which his accuracy was proportional to the extent of misorientation from the normal upright for the object-although both principal axis and feature information remain visible after picture-plane rotation. Furthermore, A.S. performed with normal accuracy, and normal pattern of reaction time performance, on tasks of mental rotation. These findings suggest that none of these traditional accounts can adequately explain why this patient was unable to recognise objects from unusual views. These findings are discussed the light of recent suggestions of the basis of this type of disorder.

Adult↗
PubMed1996

Topographic amnesia: spatial memory disorder, perceptual dysfunction, or category specific semantic memory impairment?

A 60 year old patient, SE, who presented with a severe difficulty in finding his way around previously familiar environments and a mild prosopagnosia is described. SE had herpes simplex encephalitis resulting in selective right temporal lobe damage. He showed normal spatial learning, but was severely imparied in his ability to recognise pictures of buildings and landmarks. The disorder was not confined to the visual modality, but rather involved a loss of knowledge about famous buildings and landmarks when tested from their spoken name. SE was contrasted with a more severely prosopagnosic patient, PHD, who showed normal ability to recognise buildings and landmarks, indicating that recognition of people dissociates from recognition of buildings/landmarks. It is concluded that SE's failure of place knowledge represents a category specific supramodal semantic memory impairment.

Agnosia↗
PubMed1995

Loss of remote memory: a cognitive neuropsychological perspective.

Recent, cognitively based neuropsychological studies have established that retrograde amnesia is not a single entity. Profound loss of autobiographical memory, with relative sparing of knowledge of word meaning, facts about other people and personal semantic information, may arise from either disruption of thematic retrieval frameworks or a loss of individual memory traces. The opposite pattern of profound loss of general semantic information with preservation of autobiographical memory also occurs. Finer-grained loss of semantic information, involving famous persons or other categories have also been described, providing important clues regarding the representation and organization of such knowledge.

Amnesia, Retrograde↗
PubMed1995

Object recognition without knowledge of object orientation.

Several theories have been proposed to explain our ability to recognise objects from a number of viewpoints. Orientation-dependent accounts emphasize the position of the object relative to the viewer, while orientation-independent accounts (e.g. Marr) rely on descriptions of an object's component parts relative to its principal axis of elongation. An opportunity to compare the merit of these theories has arisen in a patient (L.G.) who had a rare neuropsychological sign in which knowledge of the canonical upright of object drawings was profoundly disrupted. Such orientation errors were evident in her drawings from memory and to copy, and in an orientation-matching task. In a critical experiment she showed a deficit in providing the canonical upright of individual object drawings that was independent of any difficulty in object recognition. The implications of these data for theories of object recognition are discussed.

Adult↗
PubMed1994

Disorders of semantic memory.

It is now established that selective disorders of semantic memory may arise after focal cerebral lesions. Debate and dissension remain on three principal issues: category specificity, the status of modality-dependent knowledge, and the stability and sufficiency of stored information. Theories of category specificity have focused on the frequently reported dissociation between living things and man-made objects. However, other dimensions need theoretical integration. Impairments can be both finer-grain and broader in range. A second variable of importance is stimulus modality. Reciprocal interactive dissociations between vision and language and between animals and objects will be described. These indicate that the derivation of semantic information is constrained by input modality: we appear to have evolved separable databases for the visual and the verbal world. Thirdly, an orthogonal distinction has been drawn between degradation disorders, where representations are insufficient for comprehension, and access deficits, in which representations have become unstable. These issues may have their parallel in the acquisition of knowledge by the developing child.

Adolescent↗
PubMed1994

Multiple meaning systems in the brain: a case for visual semantics.

In this study we report our investigations of a category specific visual associative agnosia. The patient D.R.S.'s spoken language skills were excellent. Although he could name objects from their description, he was unable to name them by sight nor was he able to mime their use. On visual-visual matching tasks his performance was impaired and affected by semantic proximity. In two tasks his knowledge of visual objects was demonstrated to be significantly more impaired than his knowledge of visual living things. It is argued that these findings support a multiple knowledge base hypothesis.

Agnosia↗
PubMed1993

Midazolam-induced amnesia: implications for the implicit/explicit memory distinction.

In order to examine how the distinction between implicit and explicit memory might relate to theories regarding the organization of memory, two types of memory tests were administered in conjunction with the amnesia-inducing benzodiazepine midazolam. Performance on an implicit task (perceptual facilitation in identifying degraded pictures and words) was relatively unimpaired by midazolam, whereas performance on an explicit task (recognition memory) was severely impaired. Interpreting the results in both the implicit/explicit framework and an independent stage analysis suggests that the terms implicit and explicit may reflect something about the nature of the memory representation and need not be reserved solely to describe classes of memory tasks.

Adolescent↗
PubMed1993

Comparison of the sedative and amnesic effects of midazolam and propofol.

We have compared the sedative and amnesic effects of midazolam and propofol in 35 volunteers. Sedation was measured by simple reaction time immediately before and after a bolus injection and 1 h after the commencement of a subsequent continuous infusion. Memory was measured three times using two memory tests: perceptual facilitation provided an implicit memory measure and recognition provided an explicit memory measure. Propofol and midazolam had similar sedative effects both immediately after bolus doses and after 1-h continuous infusions of the drugs. In contrast, midazolam had a more profound amnesic effect than propofol on the recognition memory test. The drugs had little effect on performance with the implicit memory test. Performance on the memory tests was unrelated to sedation.

Adolescent↗
PubMed1993

Autobiographical amnesia resulting from bilateral paramedian thalamic infarction. A case study in cognitive neurobiology.

A patient with a chronic amnesic state resulting from bilateral paramedian thalamic infarction showed a pattern of retrograde amnesia not previously reported. Personally relevant autobiographical memory was profoundly impaired, whereas knowledge of famous people and public events was relatively spared. Furthermore, knowledge of famous people, including the ability to make accurate temporal judgements, was less affected than knowledge of public events. In addition, we have documented a severe and systematic distortion of personal memory. These findings are not compatible with current accounts of retrograde amnesia based either upon the type of information stored (e.g. episodic versus semantic memory), or upon simple storage versus access models. We propose an explanation based upon an interactive cognitive model in which the patient shows a disorder at the 'thematic retrieval framework' level of memory organization due to a disconnection of frontal and medial temporal memory systems.

Aged↗
PubMed1992

Actors but not scripts: the dissociation of people and events in retrograde amnesia.

We describe our further investigations of the retrograde amnesia in a single case. R.F.R. became globally amnesic following an attack of Herpes Simplex Encephalitis. He could generate and recognize superordinate level information about the vast majority of proper names including the names of people but he was very impaired at giving information about what had "happened" to these same individuals. He could also provide detailed information about family friends but he could not recall salient major personal episodes in which these same individuals had been involved. Knowledge of people appears to be represented in a different way to that of events, even when a singular event has provided the main or only opportunity for learning about the individual.

Amnesia, Retrograde↗
PubMed1991

Collagen I, laminin, and tenascin: ultrastructure and correlation with avian neural crest formation.

We have investigated the distribution of type I collagen, tenascin, and laminin in younger chick embryos than have previously been studied in detail. The initial appearance of type I collagen, but not tenascin and laminin, is exactly correlated with the beginning of neural crest migration, suggesting a role for collagen I in the migration. Light microscopy of whole mounts of 2-day-old chick embryos reveals that type I collagen is expressed in a rostral to caudal gradient; it localizes to the notochord sheath before accumulating around the neural tube and somites. Collagen I and tenascin also associate with central somite cells. Surprisingly, no extracellular matrix can be detected among the early sclerotomal cells, which suggests that little or no cell migration is involved in this epithelial-mesenchymal transformation. Electron microscopy using peroxidase antiperoxidase reveals that tenascin is present in nonstriated, 10 nm wide fibrils and in interstitial bodies, both of which have previously been reported to contain fibronectin. However, collagen I only occurs in the 10 nm fibrils and larger striated fibrils. This is the first ultrastructural study to assign tenascin to fibrils and interstitial bodies and to describe its appearance and disappearance from embryonic basement membranes. The discussion emphasizes the possible importance of type I collagen in neural crest cell migration and compares the ultrastructural associations of the ECM molecules present at this early embryonic stage.

Animals↗
PubMed1988

Evidence for modality-specific meaning systems in the brain.

Patients with cerebral lesions offer a unique opportunity to investigate the organization of meaning systems in the brain. Clinical neurologists have long been aware that knowledge of particular classes or categories of information may be selectively impaired in some cases and selectively spared in others. For example knowledge of letters, colours, objects, or people may be lost as a consequence of damage to the left hemisphere of the brain. Recently there has been quantitative evidence for even more specific impairment and preservation of particular classes of knowledge. More recently the evidence for knowledge of living things as compared with inanimate objects is particularly striking. Such observations have suggested that our semantic knowledge base is categorical in its organization. In this preliminary report, we describe a patient whose semantic knowledge deficit was not only category specific, but also modality specific. Although his knowledge of the visual world was almost entirely normal, his knowledge of living things (but not objects!) was gravely impaired when assessed in the verbal domain. These findings call into question the widely accepted view that the brain has a single all-purpose meaning store.

Brain↗
PubMed1988

The fractionation of retrograde amnesia.

This single case study describes our investigations of the retrograde memory deficit of a patient who became severely and selectively amnesic after an encephalitic illness. On clinical assessment his retrograde deficit for both personal and public events appeared to encompass his entire adult life. However, he retained knowledge of words introduced into the vocabulary during the retrograde period. The experimental investigation documented his inability to recall, recognize, and place in temporal order the names and faces of famous people for all time periods sampled. By contrast, his recall of either a famous face or a famous name was significantly facilitated by the verbal cue of the person's first name and initial of the surname (i.e., Margaret T...). His performance on a test of "familiarity" that required him to select the famous name or the famous face from two distractors (unknown) was within normal limits. It is argued that names and faces of famous people are represented in more than one system: both in a vocabulary-like fact memory system that is preserved and also in a congnitively mediated schemata that in this case is functionally inoperative.

Amnesia↗
PubMed1987

Categories of knowledge. Further fractionations and an attempted integration.

In this study we investigated the category specificity of the comprehension impairments of Y.O.T., a patient with a severe global dysphasia. Using matching to sample techniques it was possible to demonstrate selective impairments and selective preservations not only of broad categories of semantic knowledge but also of particular subsets of such categories. Specifically, Y.O.T.'s comprehension of 'objects' was, in general, significantly more impaired than for foods or living things. Within the broad class of objects she was significantly more impaired in the comprehension of small manipulable objects than large man-made objects. Within her proper noun vocabulary there was a significant dissociation between her good comprehension of proper nouns having a unique and well-known referent (e.g., Churchill) and common proper nouns without such a referent (e.g., Jones). Her error responses were not consistent, semantic similarity and significant rate effects were observed, and it was therefore considered that her category specific comprehension deficits were primarily ones of access to a full semantic representation. We attempt to give a principled account of the increasing number of seemingly arbitrary instances of fine-grain categorical impairments of semantic knowledge. We have suggested that different weighting values from multiple sensory channels will be important in the acquisition of different categories of knowledge and that such differential weightings could be the basis of the categorical organization of systems in the brain subserving semantic knowledge.

Aphasia↗
PubMed1987

The double dissociation of short-term memory for lists and sentences. Evidence from aphasia.

We document the sentence and list repetition skills of 3 aphasic patients. Cases 1 and 2 were classified as span-impaired conduction aphasics and Case 3 was classified as a span-preserved transcortical sensory aphasic. We found that repetition by the span-impaired cases was facilitated by increasing the 'meaningfulness' of lists, whereas this had no effect on the performance of the span-preserved case. The patients' ability to repeat sentences was contrasted with their ability to repeat three words contained in the sentences, and a double dissociation was obtained: the span-impaired cases were better at repeating sentences than in repeating three word lists whereas the span-preserved case showed the opposite pattern of difficulty. The repetition of sentences containing a known and unknown vocabulary was tested in the span-preserved case. His repetition of sentences containing words which he still knew was significantly better than his ability to repeat sentences containing a vocabulary of words which he had 'forgotten' as a consequence of his aphasia. The patients' ability to repeat complete, incomplete, and nonsense sentences was contrasted: overall the span-impaired patients were somewhat better at repeating complete sentences than incomplete sentences. Finally we examined the patients' ability both to comprehend and repeat word strings in an abbreviated 'naming from description' task: the span-impaired patients were able to comprehend three word strings, but unable to repeat them, the span-preserved case was able to repeat but not comprehend. On the basis of these double dissociations we conclude that the evidence indicates two dissociable short-term memory systems, one a relatively passive phonological store subserving list repetition, the other a dynamic, anticipatory, and integrative memory system which underpins sentence repetition.

Adult↗
PubMed1987

Understanding: a function of short-term memory?

We describe our investigations of the sentence comprehension abilities of 2 patients with a severe impairment in their auditory verbal short-term memory (conduction aphasia). Both were capable of comprehending a range of sentences, even when adequate comprehension was dependent upon the processing of order-dependent syntactic information rather than the utilization of semantic knowledge. Thus they performed satisfactorily on tests using plausibly reversible subject and object constituents with either active or passive verb phrases or prepositional phrases. Both, however, were impaired on sentences which departed from normal conversational conventions in terms of their reference to the order of event occurrence, or to the subject and object of an array. They were also very poor at performing comparative judgements, even when these involved a simple intrinsic attribute such as colour. These findings are discussed in terms of the role of auditory verbal short-term memory in backing up and back-tracking over spoken information when conditions preclude the immediate understanding of auditory-verbal information.

Adult↗