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Language is one of the pillars of human consciousness, the main implement whereby individuals articulate thoughts and convey them to others. Impairments of the brain that affect this requisite part of the human intellect stroke, head injuries, progressive conditions or developmental disorders not only disrupt a persons ability to carry out daily activities, but can also cause severe damage to the emotional state of a person and put a tremendous strain on caregivers. Pathologia physiologiam illustrat: For more than a century, it has been primarily by evidence from speech errors that neuroscientists have tried to understand the mechanisms of how the brain learns, stores, and processes language. Owing to the brains structural and functional complexity, many tasks remain unresolved. These include localizing language areas within the two hemispheres, mapping language-related functions, understanding how they relate to each other, and in what way their damage contributes to different degrees and varieties of disabilities. More specifically, the main problem remains the lack of a one-to-one correspondence between specific mental processes and cortical regions. Modern neuroscientific measurement techniques that aim at extracting quantitative information about physiological functions from image-based data may offer great insights into localized brain activity for specific cognitive tasks. For example, fMRI (functional magnetic resonance imaging) noninvasively highlights potentially significant language areas by monitoring regional changes in blood oxygenation, while PET (positron emission tomography) can measure abnormalities in the patients cerebral glucose metabolism. However, the results are highly variable from one study to the next, as there often is no single cause or pathologic mechanism, which particularly holds true for degenerative diseases. Hence, it is premature to think of functional imaging as a reliable tool to accurate diagnostic analysis as of yet, let alone grant it the power to pinpoint the internal structure and functions of the neural subsystems involved in normal language processing. A major advance in our understanding of the cortical organization of language at the systems level has not been achieved so far. It is still primarily by a number of traditional pen-and-paper neuropsychological tests that attention, perception, memory, and speech production are assessed and conclusions are being drawn about the inner mechanisms of language processing in healthy individuals in general and their altered performances under pathological circumstances in particular and the other way around. As Nickels put it, "The use of neuropsychological data rests on the assumption that patterns of language breakdown reflect the structure of the normal language system. The goal of this Magisterarbeit is to provide a critical review of the present observations in peer-reviewed literature on two well-studied but still controverted morbid conditions respectively: aphasia, a syndrome most commonly caused by a cerebrovascular event, and Alzheimers disease, or dementia of the Alzheimers type (DAT), a widely distributed, degenerative cortical disease among seniors with an unknown etiology. However diverse the symptoms of both conditions may be, they share some language impairments in the area of spoken-word production. One of the impairments, impaired single word retrieval in naming tasks, will be the focus of this investigation. This comparison is supposed to shed some light on the likelihood or unlikelihood of these two syndromes regarding lexical access. My ultimate goal is to grasp the inner nature of what essentially determines lexical access in aphasics and patients with DAT. Marshalling evidence from priming and other testings, I will engage in a discussion of the internal structure of each (assumed) component in the language system, the kinds of representations produced at each stage, and the interaction among components and subcomponents. The structure of this thesis is as follows: Chapter two briefly outlines the nature of neurophysiological damage and language disturbances in aphasics and patients with DAT. Chapter three is fitted in as an account of theoretical issues, briefly elucidating the complexity of the naming process and the boundaries of theory. The following sections constitute the main part of this thesis, focusing on a number of patterns of impaired speech output, first in Alzheimers disease (section 4) and finally in aphasia (section 5), on the basis of different results of examinations. The goal always is to draw conclusions of their underlying causative processing deficits, and incorporate the variables affecting the production of these errors. Furthermore, I will be concerned with the quantitative and qualitative differences in naming performances. For instance, aphasics show improvement when provided with verbal or orthographic cues, while Alzheimers patients hardly do so at all. Does this finding provide sufficient evidence for the assumption that the concepts in their minds simply fall victim to the decay of brain cells and tissues (atrophies)? Different studies report on Alzheimers patients showing improvement in their word finding after an intensification of visual input. Are there other, nonlinguistic factors, such as visual, perceptual, and attentional selective impairments that lead to such results? These are a few of the questions I intend to tackle in the following analyses, which are strictly theoretical in nature, giving an account of my investigations in the relevant literature. Gandhis saying, "Honest disagreement is often a good sign of progress, will finally lead me to expound my own conclusions regarding the main themes in the last sections of this thesis. The space given obviously does not allow one to exhaustively present all controversial issues currently underway, so no claim is made as to the completeness of these overviews. I will (for the most part) limit the choice of studies to the latest, and from my point of view to the most interesting available. Controversial empirical and theoretical issues will arise along the way, many of which will remain unsatisfactorily resolved. Zusammenfassung: Diese Arbeit stellt einen Überblick über den aktuellen Forschungsstand so genannter Wortfindungsstörungen dar, wie sie bei Aphasie, einer plötzlich auftretenden, umschriebenen kortikalen Läsion der linken Hemisphäre als Leitsymptom festgestellt wurden, die aber auch bei der weit verbreiteten Demenz vom Typ Alzheimer mit diffuser Hirnatrophie bereits in frühen Stadien der Krankheit eine Rolle spielen und die Kommunikation erschweren. Neben der Beschreibung der linguistischen Symptomatik werden vor allem die ursächlichen Zusammenhänge von erschwerter Wortfindung beider Syndrome in Benenntests anhand psycholinguistischer Modellvorstellungen kritisch diskutiert und verglichen. Die teilweise diametral gegenüberstehenden Ergebnisse der vorgestellten Studien resultieren aus verschiedenartigen Forschungsdesigns mit teilweise unzureichender Repräsentativität und geringem Umfang der Untersuchungsstichproben, wie sie in der Literatur häufig anzutreffen sind, weisen aber auch immer wieder auf die Komplexität und Variabilität sowohl der klassischen Aphasie als auch der Alzheimer-Demenz hin, worauf in der Arbeit mehrfach eingegangen wird. Zunächst werden Muster der erschwerten Einzelwortabfrage bei Alzheimer-Patienten kritisch besprochen, die auf eine selektive bzw. hierarchische Beeinträchtigung spezifischer semantischer Kategorien hindeuten und Aufschluss geben könnten über eine etwaige lokalistische Distribution lexikalischer Einheiten im Gehirn. Des Weiteren wird auf das sogenannte Tip of the Tongue-Phänomen eingegangen, welches auf eine temporäre Nichtverfügbarkeit der Lautstruktur des Zielwortes zurückzuführen ist, jedoch einen generellen Verlust von Konzepten ausschließt. Priming- beziehungsweise Cueing-Studien greifen die Frage nach einer degenerierten Aktivationsstruktur auf phonologischer bzw. semantischer Ebene vor dem Hintergrund einer interaktiven Netzwerkhypothese auf, wonach schließlich die These eines höheren visuellen Verarbeitungsdefizits thematisiert wird. Im anschließenden zweiten Teil der Arbeit wird der Versuch unternommen, Muster im Benennverhalten bei Aphasikern zu beschreiben, diese (soweit dies möglich ist) mit den erworbenen Erkenntnissen bei Alzheimer zu vergleichen und Rückschlüsse auf die zugrunde liegenden Mechanismen der Sprachverarbeitung zu ziehen. Dabei wird zunächst eine der wenigen komparativen Studien zum Benennen herangezogen. Anschließend wird das Thema der kategorienspezifischen Störung erneut aufgenommen, wobei nun Zusammenhänge zwischen grammatikalischen und den zuvor untersuchten semantischen Kategorien untersucht werden. Daran knüpft die Diskussion um einen etwaigen hierarchischen Verlust semantischer Konzepte an. Schlussendlich wird anhand von verschiedenen Studien zu Priming- und Cueing-Effekten gezeigt, dass die Wortfindungsstörungen bei Aphasie ähnlich wie bei Alzheimer-Demenz möglicherweise auf einer mangelnden und verzögerten Aktivation der Konzepte im semantischen Netzwerk beruhen. Eine kurze Zusammenfassung der beiden Hauptteile mit Vorschlägen zur Verbesserung der Untersuchungsdesigns schließen die Arbeit ab. Inhaltsangabe:Abstract: Language is one of the pillars of human consciousness, the main implement whereby individuals articulate thoughts and convey them to others. Impairments of the brain that affect this requisite part of the human intellect stroke, head injuries, progressive conditions or developmental disorders not only disrupt a persons ability to carry out daily activities, but can also cause severe damage to the emotional state of a person and put a tremendous strain on caregivers. Pathologia physiologiam illustrat: For more than a century, it has been primarily by evidence from speech errors that neuroscientists have tried to understand the mechanisms of how the brain learns, stores, and processes language. Owing to the brains structural and functional complexity, many tasks remain unresolved. These include localizing language areas within the two hemispheres, mapping language-related functions, understanding how they relate to each other, and in what way their damage contributes to different degrees and varieties of disabilities. More specifically, the main problem remains the lack of a one-to-one correspondence between specific mental processes and cortical regions. Modern neuroscientific measurement techniques that aim at extracting quantitative information about physiological functions from image-based data may offer great insights into localized brain activity for specific cognitive tasks. For example, fMRI (functional magnetic resonance imaging) noninvasively highlights potentially significant language areas by monitoring regional changes in blood oxygenation, while PET (positron emission tomography) can measure abnormalities in the patients cerebral glucose metabolism. However, the results are highly variable from one study to the next, as there often is no single cause or pathologic mechanism, which particularly holds true for degenerative diseases. Hence, it is premature to think of functional imaging as a reliable tool to accurate diagnostic analysis as of yet, let alone grant it the power to pinpoint the internal structure and functions of the neural subsystems involved in normal language processing. A major advance in our understanding of the cortical organization of language at the systems level has not been achieved so far. It is still primarily by a number of traditional pen-and-paper neuropsychological tests that attention, perception, memory, and speech production are assessed and conclusions are being drawn about [...
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