Spoken-word processing in aphasia: effects of item overlap and item repetition

Two studies were carried out to investigate the effects of presentation of primes showing partial (word-initial) or full overlap on processing of spoken target words. The first study investigated whether time compression would interfere with lexical processing so as to elicit aphasic-like performance in non-brain-damaged subjects. The second study was designed to compare effects of item overlap and item repetition in aphasic patients of different diagnostic types. Time compression did not interfere with lexical deactivation for the non-brain-damaged subjects. Furthermore, all aphasic patients showed immediate inhibition of co-activated candidates. These combined results show that deactivation is a fast process. Repetition effects, however, seem to arise only at the longer term in aphasic patients. Importantly, poor performance on diagnostic verbal STM tasks was shown to be related to lexical decision performance in both overlap and repetition conditions, which suggests a common underlying deficit.     

Signature tunes in mothers' speech to infants

The purpose of the present investigation was to determine whether mothers use discernible tunes (i.e., specific interval sequences) in their speech to infants and whether such tunes are individually distinctive. Mothers were recorded speaking with their infants on two occasions separated by 1 week or more. Examination of the tunes of each mother revealed discernible tunes and frequent repetitions of tunes within and across sessions. Comparisons of utterances with the most common pitch contour (i.e., rising), both within and across mothers, revealed interval patterns that were individually distinctive, or unique. The findings confirm the prominence of tunes and the presence of signature tunes in maternal speech to infants.     

Repetition blindness: an emergent property of inter-item competition

Repeating an item in a brief or rapid display usually produces faster or more accurate identification of the item (repetition priming), but sometimes produces the opposite effect (repetition blindness). We present a theory of short-term repetition effects, the competition hypothesis, which explains these paradoxical outcomes. The central tenet of the theory is that repetition produces a representation with a higher signal-to-noise ratio but also produces a disadvantage in the representation’s ability to compete with other items for access to awareness. A computational implementation of the competition hypothesis was developed to simulate standard findings in the RB literature and to generate novel predictions which were then tested in three experiments. Results from these experiments suggest that repetition effects emerge from competitive interactions between items and that these influences extend to adjacent, nonrepeated items in the display. The results also present challenges to existing theories of short-term repetition effects.     

Changes in the prevalence of alpha activity associated with the repetition,performance and magnitude of arithmetical calculations

Summary Changes in prevalence of alpha activity (defined as from 8 to 13 c.p.s.) immediately before and during the solution of twenty arithmetical tasks (multiplications and additions in Hard and Easy categories) by 61 normal subjects, with closed eyes, have been measured above a preset threshold voltage over noise level by a percent time alpha computer. An average prevalence of alpha activity of 64.75% before calculation reduced to an average prevalence of 49.01% during calculations. The prevalence of alpha activity during calculation was significantly increased by repetition of similar arithmetical tasks whereas the prevalence of alpha activity before calculation declined from the beginning to the end of the experiment, thus showing an opposite trend. Prevalence of alpha activity was not related to duration of calculations, but, in contrast, low prevalences of alpha activity during calculation were significantly associated with more numerous errors, particularly in additions. It was found that as the information content of a task increased so the prevalence of alpha activity during its solution declined, especially in additions and Easy multiplications. Calculation times and errors were strongly correlated with information content. These results are evaluated in terms of their possible behavioural significance and of the neurophysiological mechanisms underlying attenuation of alpha activity, although the precise theoretical context in which they should be viewed; whether they should be related to habituation, learning, fatigue or solely calculation, may require further clarification.

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Zusammenfassung Veränderungen in der Dominanz (Prävalenz) der Alpha-Aktivität (als 8–13 c.p.s. definiert) wurden kurz vor und während der Lösung von 20 arithmetischen Aufgaben (Multiplikation und Addition in Leichten und Schweren Serien) bei 61 normalen Personen, welche die Augen geschlossen hielten, studiert. Die Messung wurde bei einer festgesetzten (preset) Schwellenspannung über dem Geräuschniveau mit einem Alpha-Zeit-Computer ausgeführt. Dabei ergab sich eine Reduzierung der Alpha-Aktivität von 64,75% vor dem Rechnen auf 49,01% während des Rechnens. Die Alpha-Dominanz während des Rechnens wurde statistisch durch Wiederholung von ähnlichen Aufgaben erhöht; im Gegensatz dazu ging die Alpha-Dominanz vor dem Rechnen progressiv vom Anfang bis zum Ende des Experiments zurück.Die Alpha-Dominanz hatte keine Beziehung zur Dauer des Rechnens; andererseits waren niedrige Frequenzen von Alpha-Aktivität während des Rechnens mit Häufigkeit von Fehlern, vor allem beim Addieren, verbunden. Wenn sich der Informations-inhalt einer Aufgabe erhöhte, so verminderte sich die Alpha-Dominanz während ihrer Lösung, vor allem beim Addieren und bei leichten Multiplikationen. Sowohl Rechen-Zeit wie Fehler waren stark mit dem Informations-inhalt korreliert.Diese Ergebnisse werden hinsichtlich ihrer möglichen Beziehungen zum psychischen Verhaltens-Zustand (Behaviour) und zu den mit Abschwächung der Alpha-Aktivität verbundenen neuro-physiologischen Prozessen analysiert. Eine Klärung des präzisen theoretischen Zusammenhanges, in dem die Resultate gesehen werden sollten, sowie ihre Beziehungen zu Gewöhnung, Lernen, Ermüdung oder zum Rechnen allein, erfordert weiteres Studium.

     

Effects of stimulus features and instruction on response coding,selection, and inhibition: Evidence from repetition effects under task switching

The coding of stimuli and responses is crucial for human behaviour. Here, we focused primarily on the response codes (or response categories). As a method, we applied a combined dual-task and task-switch paradigm with a fixed task-to-hand mapping. Usually, negative effects (i.e., costs) are observed for response category repetitions under task switching. However, in several previous studies it has been proposed that such repetition effects do not occur, if the stimulus categories (e.g., “odd” if digits have to be classified according to their parity feature) are unequivocally mapped to specific responses. Our aim was to test this hypothesis. In the present experiments, we were able to distinguish between three different types of possible response codes. The results show that the participants generally code their responses according to abstract response features (left/right, or index/middle finger). Moreover, the spatial codes were preferred over the finger-type codes even if the instructions stressed the latter. This preference, though, seemed to result from a stimulus–response feature overlap, so that the spatial response categories were primed by the respective stimulus features. If there was no such overlap, the instructions determined which type of response code was involved in response selection and inhibition.     

On the joint effects of repetition and stimulus quality in lexical decision: Looking to the past for a new way forward

Two experiments investigated the joint effects of stimulus quality and repetition in the context of lexical decision. Experiment 1 yielded an interaction between repetition and stimulus quality for words (but additive effects for nonwords) when the lag was short, replicating previous reports. Experiment 2, with a much longer lag than Experiment 1, yielded main effects of stimulus quality and repetition, but these factors no longer interact. The joint effects of stimulus quality and repetition for words as a function of lag can be understood in terms of two loci for repetition effects: one short-term and one long-term. The transient effect of repetition is on activation levels in the lexicons (and in which the input lexicon, but not beyond, is affected by stimulus quality), whereas the long-term effect is on the strength of two-way connections between lexical–lexical and lexical–semantic modules. These data and others, taken together with the account, provide a new way of thinking about a 30-year-old conundrum.     

Orientation-invariant object recognition: evidence from repetition blindness

The question of whether object recognition is orientation-invariant or orientation-dependent was investigated using a repetition blindness (RB) paradigm. In RB, the second occurrence of a repeated stimulus is less likely to be reported, compared to the occurrence of a different stimulus, if it occurs within a short time of the first presentation. This failure is usually interpreted as a difficulty in assigning two separate episodic tokens to the same visual type. Thus, RB can provide useful information about which representations are treated as the same by the visual system. Two experiments tested whether RB occurs for repeated objects that were either in identical orientations, or differed by 30, 60, 90, or 180 degrees . Significant RB was found for all orientation differences, consistent with the existence of orientation-invariant object representations. However, under some circumstances, RB was reduced or even eliminated when the repeated object was rotated by 180 degrees , suggesting easier individuation of the repeated objects in this case. A third experiment confirmed that the upside-down orientation is processed more easily than other rotated orientations. The results indicate that, although object identity can be determined independently of orientation, orientation plays an important role in establishing distinct episodic representations of a repeated object, thus enabling one to report them as separate events.     

Conceptual and non-conceptual repetition priming in category exemplar generation: Evidence from bilinguals

One measure of conceptual implicit memory is repetition priming in the generation of exemplars from a semantic category, but does such priming transfer across languages? That is, do the overlapping conceptual representations for translation equivalents provide a sufficient basis for such priming? In Experiment 1 (N=96) participants carried out a deep encoding task, and priming between languages was statistically reliable, but attenuated, relative to within-language priming. Experiment 2 (N=96) replicated the findings of Experiment 1 and assessed the contributions of conceptual and non-conceptual processes using a levels-of-processing manipulation. Words that underwent shallow encoding exhibited within-language, but not between-language, priming. Priming in shallow conditions cannot therefore be explained by incidental activation of the concept. Instead, part of the within-language priming effect, even under deep-encoding conditions, is due to increased availability of language-specific lemmas or phonological word forms.     

Flexible target representations underlie repetition priming in visual search

Repeating target features across consecutive visual search trials can influence response time. Three experiments are reported that show that this repetition priming is dependent on the exact stimulus configuration and feature type. In Experiment 1 the target was defined relative to distractors by its orientation and target colour was task irrelevant. The roles played by these features were reversed in Experiment 2. Repeating target colour across trials speeded responses in both Experiments 1 and 2. Repeating orientation significantly slowed responses in Experiment 1 but had no significant effect in Experiment 2. Existing feature-based and episodic memory-based explanations of priming cannot account for these data, but instead more flexible explanations are required. Experiment 3 showed that significant positive priming results from repeating distractor-defining orientation, indicating that priming of pop-out effects previously reported in the literature may result from combined target and distractor effects.     

Word-specific repetition effects revealed by MEG and the implications for lexical access

This magnetoencephalography (MEG) study investigated the early stages of lexical access in reading, with the goal of establishing when initial contact with lexical information takes place. We identified two candidate evoked responses that could reflect this processing stage: the occipitotemporal N170/M170 and the frontocentral P2. Using a repetition priming paradigm in which long and variable lags were used to reduce the predictability of each repetition, we found that (i) repetition of words, but not pseudowords, evoked a differential bilateral frontal response in the 150–250 ms window, (ii) a differential repetition N400m effect was observed between words and pseudowords. We argue that this frontal response, an MEG correlate of the P2 identified in ERP studies, reflects early access to long-term memory representations, which we tentatively characterize as being modality-specific.