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Using positron emission tomography, visual presentation of sentences was shown to cause increased regional cerebral blood flow relative to word lists in the left lateral anterior superior and middle temporal gyri, attributable to cognitive processes that occur during sentence comprehension in addition to those carried out during word comprehension. Additional comparisons showed that repeating words (in a different context, when subjects did not attempt to learn the initial lists) led to significant patterns of both increased blood flow (left putamen and right caudate) and decreased blood flow (left posterior temporal lobe). Increases are argued to reflect retrieval of memory traces, whereas decreases reflect diminished necessity for processing of input. A decrease in the left inferior parietal lobe was attributable to other factors. [ABSTRACT FROM AUTHOR]

In two experiments, event-related brain potentials were recorded to word pairs simultaneously presented to both ears, with instructions to attend to one ear and detect occasional nonwords in that ear. This attentional manipulation yielded four patterns of word repetition on successive trials: first and second presentations attended (AA), both unattended (UU), and across ears (AU and UA). A prominent attenuation of N400 due to immediate repetition of words was observed on AA trials. However, when first presentations were ignored on UU and UA trials, no repetition effect was obtained. These findings indicate that the repetition effect on N400 depends on attentional processing of first presentations. [ABSTRACT FROM AUTHOR]

Event-related potentials (ERPs) were recorded while subjects viewed visually presented words, some of which occurred twice. Each trial consisted of two colored letter strings, the requirement being to attend to and make a word/nonword discrimination for one of the strings. Attention was manipulated by color in Experiment 1, and color and a precue were used in Experiment 2. As in previous ERP studies of word repetition, a positive offset to repeated words developed when both first and second presentations were the focus of attention. In Experiment 2, ERPs showed evidence of positive-going repetition effects in all conditions in which at least one of the two presentations of the repeated word was attended. In the visual modality, the positive-going ERP repetition effect occurs only when at least one of the two presentations of a repeated item is the object of attention, which suggests that one or more of the processes reflected by the effect is capacity limited. [ABSTRACT FROM AUTHOR]

We recorded event-related potentials while subjects performed a category membership decision task. The stimuli were words of high and low frequency of occurrence in written English, and each was presented four times. The experiment was intended to explore the interaction of word frequency and multiple repetition on the event-related potential, and thence to investigate the possible loci in time of the effects of these variables. First presentations of low and high frequency words evoked event-related potentials which differed in the presence, in the low word frequency waveforms, of a right-hemisphere dominant negativity peaking at 400 ms. This negativity was very similar to the N400 which may be sensitive to the semantic relations among words in a sequence. Initial repetition diminished this midlatency difference, but gave rise to both earlier and later frequency-related differences. Subsequent multiple repetition abolished the early frequency-related repetition effect, but did not affect amplitudes in the region of N400, nor did it abolish a late positivity, present only for repeated low frequency words. [ABSTRACT FROM AUTHOR]

The modulation of event-related potentials by word repetition was investigated in two experiments. In both experiments, subjects responded to occasional nonwords interspersed among a series of words. A proportion of the words were repetitions of previously presented items. Words were repeated after 0 or 6 intervening items in Experiment 1 and after 6 or 19 items in Experiment 2. Event-related potentials to repeated words were characterised by a sustained, widespread positive-going shift with in onset of approximately 300 ms. This effect did not vary significantly as a function of lag in either experiment. When words were repeated immediately, this repetition evoked positive shirt was preceded by a transient negative deflection (onset ca. 200 ms) which was absent in event-related potentials to words repeated at longer lags. These results suggest that the modulation of event-related potentials by word repetition is influenced by at least two processes. One of these processes acts relatively early during the processing of a repeated word, but subsides rapidly as inter-item lag between first fad second presentations increases. The second process occurs inter in time, but is considerably more robust over variations in inter-item lag. [ABSTRACT FROM AUTHOR]