Predictability's aftermath: Downstream consequences of word predictability as revealed by repetition effects

Stimulus processing in language and beyond is shaped by context, with predictability having a particularly well-attested influence on the rapid processes that unfold during the presentation of a word. But does predictability also have downstream consequences for the quality of the constructed representations? On the one hand, the ease of processing predictablewordsmight free up time or cognitive resources, allowing for relatively thorough processing of the input. On the other hand, predictabilitymight allowthe systemto run in a top-down “verificationmode”, at the expense of thorough stimulus processing. This electroencephalogram (EEG) study manipulated word predictability, which reduced N400 amplitude and inter-trial phase clustering (ITPC), and then probed the fate of the (un)predictable words in memory by presenting them again. More thorough processing of predictable words should increase repetition effects, whereas less thorough processing should decrease them. Repetition was reflected in N400 decreases, late positive complex (LPC) enhancements, and late alpha/beta band power decreases. Critically, prior predictability tended to reduce the repetition effect on the N400, suggesting less priming, and eliminated the repetition effect on the LPC, suggesting a lack of episodic recollection. These findings converge on a top-down verification account, on which the brain processes more predictable input less thoroughly. More generally, the results demonstrate that predictability hasmultifaceted downstreamconsequences beyond processing in the momen

Investigating the Electrophysiology of Long-Term Priming in Spoken Word Recognition

When participants are listening to the same words spoken by different talkers, two types of priming are possible: repetition priming and talker-specific priming. Repetition priming refers to the exposure of a stimulus improving responses to a subsequent exposure. Talker-specific priming refers to the exposure of words spoken by same talkers improving responses relative to those same words spoken by different talkers. There are conflicting theories regarding whether talker-specific priming should be observed. Abstract representational theories suggest that episodic details (e.g., talker identity) are not stored in the mental lexicon, while episodic theories of the lexicon posit that lexical representations include episodic details. According to the time-course hypothesis, the mental lexicon includes both types of representations, and abstract representations are accessed earlier than episodic representations. In the present experiment, long-term priming in spoken word recognition was tested using a technique that is particularly well-suited for answering questions about timing: event-related potentials (ERPs). Participants heard words spoken by two different talkers in each of two separate blocks. Stimuli in the second block consisted of three different priming conditions, which are described in relation to what participants heard in the first block: new, unprimed, words (control), repeated words spoken by the same talker (match), and repeated words spoken by different talkers (mismatch). Evidence for long-term repetition priming was obtained in reaction times and accuracy. Electrophysiological evidence of repetition priming was obtained in low frequency words. Talker-specific priming effects were observed in accuracy, with more accurate responses in the match condition than in the mismatch condition, consistent with episodic representational theories. However, there was no evidence of talker-specific priming in the ERP data, which, when considered alone, is consistent with abstract representational theories. The current results provide the first physiological evidence (ERPs) of long-term repetition priming in spoken word recognition, setting the stage for future empirical investigations

Development of auditory repetition effects with age : evidence from EEG time-frequency analysis

La présentation répétée d’un son inconnu conduit à des effets de répétition comprenant la suppression (‘repetition suppression’ ou RS) ou l’augmentation (‘repetition enhancement’ ou RE) de l’activité neuronale. Ces phénomènes reflètent des mécanismes cérébraux impliquant un apprentissage perceptuel. L’objectif de ce mémoire de maitrise était d’apporter une perspective développementale de l’activité cérébrale sous-tendant l’apprentissage perceptuel auditif. L’EEG a été enregistré chez 101 participants sains âgés de 3 à 40 ans pendant un paradigme auditif passif durant lequel 30 pseudo-mots étaient répétés 6 fois chacun. Des analyses en temps- fréquence ont été calculées pour chaque répétition. La puissance spectrale enregistrées en EEG entre chaque répétition a été comparée au moyen de modèles linéaires mixtes. Les résultats montrent qu’un effet de répétition survient au cours du développement mais varie en fonction de l’âge et des bandes de fréquences. Du RS et RE ont été observés à tous les âges dans le thêta bas et le gamma respectivement. Un effet développemental a été trouvé de façon plus précoce pour le RS dans le thêta haut et de façon tardive pour le RE dans le thêta bas. Ces résultats montrent que les processus impliquant un apprentissage perceptif auditif, tel que le RS et le RE, suivent une trajectoire développementale spécifique en fonction des rythmes cérébraux. Les effets de répétition reflèteraient différents niveaux de traitement des stimuli qui se développeraient de manière indépendante. Des recherches supplémentaires seront nécessaires pour préciser le rôle fonctionnel des effets de répétitions sur le développement cognitif.The repeated presentation of unfamiliar sounds leads to repetition effects comprising repetition suppression (RS) and enhancement (RE) of neural activity. These phenomena reflect mechanisms involved in perceptual learning and are associated with a decrease or increase in EEG spectral powers. The objective of this Master’s thesis is to provide a developmental perspective of the cortical activity underlying auditory perceptual learning. EEG was recorded in 101 healthy participants ranging from 3 to 40 years during an auditory paradigm comprising 30 pseudowords repeated six times each. EEG time-frequency spectral power was calculated for each presentation and was compared to quantify repetition effects. Linear mixed model analysis revealed that some repetition effects occurred across ages and others varied with age in specific frequency bands. More precisely, RS and RE were found across ages in lower theta and gamma frequency bands respectively between the first and all subsequent pseudoword presentations. Developmental effects were seen in the RS observed in the higher theta/low alpha band and in the later occurring RE in the lower theta band. These results show that processes involved in auditory perceptual learning, such as RS and RE, are modulated by maturation. Further, repetition effects reflect different levels of stimulus processing and these levels seem to develop independently. More research is required to identify the exact functional roles of auditory repetitions effects on cognitive development

Semantic radical consistency and character transparency effects in Chinese: an ERP study

BACKGROUND: This event-related potential (ERP) study aims to investigate the representation and temporal dynamics of Chinese orthography-to-semantics mappings by simultaneously manipulating character transparency and semantic radical consistency. Character components, referred to as radicals, make up the building blocks used dur...postprin

Not all disfluencies are are equal: The effects of disfluent repetitions on language comprehension

Disfluencies can affect language comprehension, but to date, most studies have focused on disfluent pauses such as er. We investigated whether disfluent repetitions in speech have discernible effects on listeners during language comprehension, and whether repetitions affect the linguistic processing of subsequent words in speech in ways which have been previously observed with ers. We used event-related potentials (ERPs) to measure participants’ neural responses to disfluent repetitions of words relative to acoustically identical words in fluent contexts, as well as to unpredictable and predictable words that occurred immediately post-disfluency and in fluent utterances. We additionally measured participants’ recognition memories for the predictable and unpredictable words. Repetitions elicited an early onsetting relative positivity (100–400 ms post-stimulus), clearly demonstrating listeners’ sensitivity to the presence of disfluent repetitions. Unpredictable words elicited an N400 effect. Importantly, there was no evidence that this effect, thought to reflect the difficulty of semantically integrating unpredictable compared to predictable words, differed quantitatively between fluent and disfluent utterances. Furthermore there was no evidence that the memorability of words was affected by the presence of a preceding repetition. These findings contrast with previous research which demonstrated an N400 attenuation of, and an increase in memorability for, words that were preceded by an er. However, in a later (600–900 ms) time window, unpredictable words following a repetition elicited a relative positivity. Reanalysis of previous data confirmed the presence of a similar effect following an er. The effect may reflect difficulties in resuming linguistic processing following any disruption to speech

The face-specific N170 component is modulated by emotional facial expression

BACKGROUND: According to the traditional two-stage model of face processing, the face-specific N170 event-related potential (ERP) is linked to structural encoding of face stimuli, whereas later ERP components are thought to reflect processing of facial affect. This view has recently been challenged by reports of N170 modulations by emotional facial expression. This study examines the time-course and topography of the influence of emotional expression on the N170 response to faces. METHODS: Dense-array ERPs were recorded in response to a set (n = 16) of fear and neutral faces. Stimuli were normalized on dimensions of shape, size and luminance contrast distribution. To minimize task effects related to facial or emotional processing, facial stimuli were irrelevant to a primary task of learning associative pairings between a subsequently presented visual character and a spoken word. RESULTS: N170 to faces showed a strong modulation by emotional facial expression. A split half analysis demonstrates that this effect was significant both early and late in the experiment and was therefore not associated with only the initial exposures of these stimuli, demonstrating a form of robustness against habituation. The effect of emotional modulation of the N170 to faces did not show significant interaction with the gender of the face stimulus, or hemisphere of recording sites. Subtracting the fear versus neutral topography provided a topography that itself was highly similar to the face N170. CONCLUSION: The face N170 response can be influenced by emotional expressions contained within facial stimuli. The topography of this effect is consistent with the notion that fear stimuli exaggerates the N170 response itself. This finding stands in contrast to previous models suggesting that N170 processes linked to structural analysis of faces precede analysis of emotional expression, and instead may reflect early top-down modulation from neural systems involved in rapid emotional processing

Continuous-speech segmentation at the beginning of language acquisition: Electrophysiological evidence

Word segmentation, or detecting word boundaries in continuous speech, is not an easy task. Spoken language does not contain silences to indicate word boundaries and words partly overlap due to coarticalution. Still, adults listening to their native language perceive speech as individual words. They are able to combine different distributional cues in the language, such as the statistical distribution of sounds and metrical cues, with lexical information, to efficiently detect word boundaries. Infants in the first year of life do not command these cues. However, already between seven and ten months of age, before they know word meaning, infants learn to segment words from speech. This important step in language acquisition is the topic of this dissertation. In chapter 2, the first Event Related Brain Potential (ERP) study on word segmentation in Dutch ten-month-olds is discussed. The results show that ten-month-olds can already segment words with a strong-weak stress pattern from speech and they need roughly the first half of a word to do so. Chapter 3 deals with segmentation of words beginning with a weak syllable, as a considerable number of words in Dutch do not follow the predominant strong-weak stress pattern. The results show that ten-month-olds still largely rely on the strong syllable in the language, and do not show an ERP response to the initial weak syllable. In chapter 4, seven-month-old infants' segmentation of strong-weak words was studied. An ERP response was found to strong-weak words presented in sentences. However, a behavioral response was not found in an additional Headturn Preference Procedure study. There results suggest that the ERP response is a precursor to the behavioral response that infants show at a later age