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Biomedical subjects

M M Keane

Publications and source records attributed to M M Keane.

28 records · Page 2Linked to original sources
PubMed1995

Normal perceptual priming of orthographically illegal nonwords in amnesia.

This study examined priming in perceptual identification of orthographically illegal nonwords in control subjects and patients with global amnesia. Subjects studied a list of orthographically illegal nonwords and then performed a perceptual identification task in which half of the stimuli were from the prior study list and half were new (unstudied) stimuli. Priming was reflected in enhanced identification accuracy of studied compared to unstudied nonwords. Amnesic patients showed significant and normal priming despite impaired recognition memory performance. Because the experimental stimuli were dissimilar to real words in terms of orthography and phonology, it is unlikely that this priming effect was mediated by activation of pre-existing representations of orthographically or phonologically similar words, morphemes, or syllables. These results demonstrate that intact perceptual priming in amnesia is not limited to stimuli that are premorbidly represented in long-term knowledge, nor to novel stimuli that conform to the rules that characterize familiar items. Further, because the experimental stimuli comprised novel letter assemblies, the results suggest that amnesic patients can show normal priming for new perceptual associations. These findings demonstrate that processes spared in amnesia can support the creation and subsequent retrieval of novel stimulus representations.

Adult↗
PubMed1995

Double dissociation of memory capacities after bilateral occipital-lobe or medial temporal-lobe lesions.

Memory for recently encountered information can be reflected in conscious recall and recognition of that material, or in facilitated reprocessing of that material, an effect known as repetition priming. Repetition priming may be perceptual (form-based) or conceptual (meaning-based). A patient with bilateral occipital-lobe lesions (L.H.) and a patient with bilateral medial-temporal lobe lesions (H.M.) showed a double dissociation between visuoperceptual priming (impaired in L.H. and intact in H.M.) and visual recognition memory (intact in L.H. and impaired in H.M.). L.H. showed intact conceptual priming for visually presented words; his pattern of impaired visuoperceptual priming and intact conceptual priming is the reverse dissociation to that observed in prior studies of patients with Alzheimer's disease, in whom occipital cortices are relatively spared. These double dissociations suggest that a memory system localized to the occipital lobe mediates visuoperceptual priming effects, and that this system is independent of neural circuits mediating conceptual priming effects, and independent of the limbic-diencephalic system supporting conscious recognition of recently encountered information.

Adult↗
PubMed1994

Priming in perceptual identification of pseudowords is normal in Alzheimer's disease.

Patients with Alzheimer's disease (AD) have deficits in recall and recognition memory, and show dissociable performance in repetition priming tasks: They exhibit impaired priming in word-completion and word-generation tasks, but normal priming is perceptual identification of words. In order to examine whether AD patients can show normal priming with novel, unfamiliar stimuli, the present study examined their performance in perceptual identification of pseudowords. Despite impaired recognition memory performance, AD patients showed normal priming in perceptual identification of pseudowords. These results extend the boundaries of intact repetition priming in AD, demonstrating that such priming is not limited to stimuli that are pre-morbidly represented in long-term knowledge. Preserved repetition priming in AD may reflect the operation of perceptual processes localized to posterior visual circuits that are relatively spared in AD.

Aged↗
PubMed1994

Dissociations among structural-perceptual, lexical-semantic, and event-fact memory systems in Alzheimer, amnesic, and normal subjects.

Patients with Alzheimer's disease (AD), patients with global amnesia (AMN), and normal control (NC) subjects received tests of recall and recognition, word-completion priming, and incomplete-picture priming. The AD and AMN patients had impaired recall and recognition. The AD patients, but not the AMN patients, had impaired word-completion priming. In contrast, the AD patients had intact incomplete-picture priming, a form of priming shown to be perceptual in normal subjects. These results provide neuropsychological evidence for a dissociation between two components of repetition priming, perceptual priming as measured with identification tasks and nonperceptual priming as measured with generation tasks. Preserved perceptual priming in AD may be mediated by the occipital regions that are relatively spared in AD; compromised nonperceptual priming may be mediated by temporal regions that show dense neuropathological changes early in AD.

Adult↗
PubMed1994

Bcl-2 rearrangement in Hodgkin's disease and reactive lymph nodes.

The chromosomal translocation t(14;18)(q32;q21), which involves the bcl-2 oncogene, occurs in most follicular lymphomas. Recent evidence suggests that this translocation occurs in Hodgkin's disease, linking its cellular origin and oncogenesis to follicular non-Hodgkin's lymphomas. Using polymerase chain reaction, the authors examined both Hodgkin's disease (n = 60) and reactive lymph nodes (n = 34) for the presence of bcl-2/JH breakpoint fragments, which are indicative of the t(14;18) chromosomal translocation in the major breakpoint region of the bcl-2 gene. The translocation was detected in approximately 10% of both Hodgkin's disease and nonmalignant reactive lymph node cases. These results suggest the possibility that the translocation may occur in the reactive component of Hodgkin's disease and not in the putative malignant cells, the Reed-Sternberg cells. Furthermore, the detection of the translocation in reactive lymph nodes suggests that it may not be the primary factor in the oncogenesis of follicular lymphoma.

Base Sequence↗
PubMed1993

Angiosarcoma arising from a defunctionalized arteriovenous fistula.

We report a case of angiosarcoma developing in a defunctionalized arteriovenous fistula that had been created for hemodialysis approximately 20 years previously. At presentation the patient had a 30-year history of chronic renal failure and had undergone renal transplantation 10 years previously.

Arteriovenous Shunt, Surgical↗
PubMed1992

Category knowledge in Alzheimer's disease: normal organization and a general retrieval deficit.

Three hypotheses that could account for deficits in the retrieval of category information in Alzheimer's disease (AD) were evaluated: abnormal organization, class- or category-specific vulnerability, and limitation by general factors, such as decreased processing speed. Relative to 18 elderly control subjects, 18 patients with AD produced fewer items in a category fluency task and had longer reaction times in a category decision task. The pattern of performance across categories on both tasks was normal in the AD group: The same categories elicited the most (or fastest) responses in both the control group and the AD group. AD patients showed normal performance in ranking of category exemplars by typicality. There was no evidence for differential accessibility by category or by class of information (animate vs. inanimate). The authors conclude that a general factor or factors limit(s) retrievability equally across all categories.

Aged↗
PubMed1991

Evidence for a dissociation between perceptual and conceptual priming in Alzheimer's disease.

The status of perceptual priming and word-completion priming in patients with Alzheimer's disease (AD) was examined. Experiment 1 established the reliability of the perceptual priming measure in normal subjects. In Experiment 2, AD patients showed a normal magnitude of perceptual priming. In Experiment 3, a single group of AD patients showed a normal magnitude of perceptual priming and impaired word-completion priming. Further, word-completion priming, but not perceptual priming, was correlated with verbal fluency performance in AD. These results suggest a dissociation between two components of verbal priming. Perceptual priming may reflect the operation of a structural-perceptual memory system mediated by occipital lobe regions relatively spared in AD. Word-completion priming may reflect the operation of a lexical-semantic memory system mediated by temporoparietal lobe regions compromised in AD.

Adult↗
PubMed1990

Intact priming of patterns despite impaired memory.

The priming of patterns was examined in normal control subjects (NCS) and in the amnesic patient H.M., whose anterograde amnesia followed bilateral medial temporal-lobe excision 33 years earlier. Despite H.M.'s impaired recognition of the patterns, he demonstrated a pattern priming effect equivalent in magnitude to that of the NCS. The results demonstrated that intact priming with novel, nonverbal material can occur despite severe amnesia. Pattern priming may reflect adaptive visual processes involved in learning novel perceptual organizations of known visual codes, such as letters, words, shapes, and objects.

Amnesia↗