Abstract
Zusammenfassung. Lesen ist für die meisten Menschen ein stark automatisierter, komplexer mentaler Vorgang, der einmal erlernt, scheinbar bis ins hohe Alter stabil erhalten bleibt. Dabei können tiefere Textverständnisprozesse, ebenso wie reflektive oder ästhetische Vorgänge (z. B. bei der Poesierezeption) nur dann effizient ablaufen, wenn die zugrunde liegende Einzelworterkennung flüssig funktioniert. Während der Leseerwerb im Bereich der Einzelworterkennung intensiv erforscht wurde, existieren kaum Studien, welche die Entwicklung der visuellen Worterkennung im Alter systematisch untersucht haben. Dies ist verwunderlich, wenn man bedenkt, dass der Umgang mit Wörtern, Sprache und Texten kognitive Prozesse rekrutiert, die im Alter von einem Rückgang neurochemischer, -anatomischer und funktionaler Ressourcen gekennzeichnet sind. Daher war Ziel dieser Arbeit, eine Übersicht der bisherigen Forschung von Alterseffekten auf die visuelle Worterkennung zu geben, die den aktuellen Forschungsstand zusammenzufasst. Im Fokus standen dabei Variablen, mit denen typischerweise lexikalische Prozesse und sublexikalische Prozesse operationalisiert werden. Es wurden 16 Studien identifiziert, die Wortfrequenz-, Längen- und orthographische Nachbarschaftseffekte im Alter sowohl auf Verhaltensebene als auch auf neuronaler Ebene untersucht haben. Die Ergebnisse sprechen dafür, dass die visuelle Wortverarbeitung im Bereich der Ganzworterkennung bis ins hohe Alter relativ intakt und in ihrer Ausprägung annähernd konstant bleibt. Während Frequenzeffekte im Alter vergleichbar zu denen jüngerer Leser sind, könnten lexikalische Inhibitions- und Aktivierungsprozesse von Veränderungsprozessen im Alter betroffen sein. Die Ergebnisse zum Wortlängeneffekt sind ambivalent, könnten aber auf altersbedingte Unterschiede in den sublexikalischen Prozessen hindeuten. Gleichzeitig wird ein Mangel an neurokognitiven und deutschsprachigen Studien sichtbar.
Abstract.Background: Reading is a highly automized, complex mental process that, once acquired, functions efficiently for most people. Text comprehension as well as reflective or aesthetic processes (e. g., in poetry reception) can only be performed effortlessly at a high level when the underlying single word recognition runs smoothly. In fact, single word recognition appears as important for developing key concepts in cognitive psychology and psycholinguistics as the cell in biology. While factors influencing reading acquisition as well as reading processes in young adults have been extensively investigated across different languages, only a small number of studies focussed on developmental aspects of visual word recognition over the life span, i. e. on changes that might occur during aging and/or in old age. Considering that handling words, speech, and texts recruits cognitive processes that are all marked by a decline in neurochemical, neuroanatomical and functional resources with increasing age this seems rather astonishing, even more so as this deficiency was already noted almost 20 years ago. Aims: The aim of this review is threefold. First, we give a summary of the research on visual word recognition in young adult readers. This includes describing common paradigms, major findings regarding key variables and methods, as well as a short description of popular models of word recognition. Second, we summarize findings of studies investigating age effects on visual word recognition and provide an overview on the current state of affairs within that field. Third, we discuss chief findings and their implications for future research. Methods: As the lexical decision task is explicitly recommended to investigate single word recognition only studies using this task entered the review. To determine whether age affects processing on the whole word level or on a sublexical level (e. g., syllables) we looked at frequency and orthographic neighborhood effects (word level), as well as at length effects (sublexical level) and their interaction with age. We were able to identify 16 studies that met the selection criteria. Only results obtained from healthy, normal reading adults are reported. The age span covered by this review ranges from 17 to 88 years. Results: By far, most studies concentrated on frequency effects as a function of age. From 15 studies addressing this topic, 12 reported no significant interaction of age and frequency, i. e. there is no evidence for any differences between young and older participants. Both age groups responded equally faster to high frequency than to low frequency words. Only two studies found larger frequency effects for older than for younger adults with one of these two studies reporting that result for both the lexical decision task and naming task, yet not for the lexical decision task alone. One study reported no interaction between frequency and age at first but reported larger frequency effects for younger than for older adults after adjusting the young subjects’ latency data to that of the older ones. Length effects as a function of age were addressed in six studies. Two of them found significant interactions between word length and age. Larger length effects were reported for older participants than for younger participants. Two studies did not find any differences between the age groups. Two other studies reported a significant word length disadvantage for older adults but only after adjusting the younger subjects' latency data to that of the old ones; without adjustment no interaction between word length and age could be found. Only three studies could be identified that looked into orthographic neighborhood effects as a function of age. While one study reported no effects of orthographic neighborhood for both the younger and older adults two studies found smaller neighborhood effects for older participants than for younger participants: Older adults tended to respond more slowly to words with a high neighborhood density than did younger adults, younger adults responded more slowly to words with a high neighborhood frequency whereas older adults showed no such effect. Neuronal effects of word frequency and word length as a function of age were addressed in only one study by means of cerebral blood flow. Solely for older participants frequency effects were found in Brodmann Areas (BA) 17, 18 and 37 in the left hemisphere. The slower they responded to low frequent words, the more activation older adults produced in these areas. Likewise, only older adults showed word length effects in BA 17 with activity being larger the less influence word length had on reaction time. No neuronal effects of word frequency and word length were obtained for the younger age group. Discussion: There is a variety of reasons that can generally account for the variability in findings which every researcher in the field of age effects in language processing should be aware of. First, there is an ongoing debate whether vocabulary scores of older and younger adults should be matched or not. Naturally, older adults should have an advantage over younger adults in vocabulary knowledge due to their prolonged exposure to language. However, matching the scores might confound results. Second, besides vocabulary there are further important variables such as time of formal education and acuity that should be taken into account. Especially acuity seems to have an enormous effect in recognition tasks, but information on this issue is omitted in a number of studies of this review. Third, as a rule, reaction times of older participants are longer than those of younger participants, making special analyses necessary: Yet, there are different approaches taken by different research groups. Furthermore, aging per se is an extremely heterogeneous process leaving some older participants operate on a fairly high level, while others show clear signs of cognitive decline. As a consequence, variance in data is larger in the older age group than in the younger. When it comes to differences in results reported for frequency effects as a function of age three explanations are brought forward. First, objective frequency measures correspond more to the lexicon of older adults than to that of younger adults. Second, when comparing older and younger participants with similar vocabulary scores chances are, that these older participants are more likely to be less competent readers. Less competent readers, in turn, tend to produce larger frequency effects than competent ones. Third, the level of education influences the magnitude of the frequency effect as well. Less educated subjects produce a more pronounced frequency effect than do educated ones. Yet, all three explanations do not fully account for the reported results. Differences in results concerning the length effect as a function of age might be due to characteristics of the stimulus material. But as not all details describing the stimuli are given in the studies this conclusion remains speculative. Results concerning orthographic neighborhood point towards decreased lexical activation and inhibition in older adults. Neuronally, findings suggest that older and younger adults process frequency and word length differently. Conclusion: To answer the question whether reading changes with age one obviously has to consider the different subprocesses of reading. Lexical processing which is crucial for word recognition seems to be only partially affected by age. The lack of an interactive effect of frequency and age suggests visual word recognition to be relatively stable over the lifetime. Yet, results reported for orthographic neighborhood point towards a change in lexical inhibition and activation processes in older adults. Age-dependent changes in reading seem to emerge most notably at the sublexical level as findings concerning word length effects indicate.
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