Cortical auditory processing of informational masking effects by target-masker similarity and stimulus uncertainty

Purpose: Understanding speech in a background of other people talking is one of the most difficult listening challenges for hearing-impaired individuals, and even for those with normal hearing. Speech-on-speech masking, is known to contribute to increased perceptual difficulty over non-speech background noise because of informational masking provided over and above the energetic masking effect. While informational masking research has identified factors of similarity and uncertainty between target and masker that contribute to reduced behavioral performance in speech background noise, critical gaps in knowledge including the underlying neural-perceptual processes remain. By systematically manipulating aspects of similarity and uncertainty in the same auditory paradigm, the current study proposed to examine the time course and objectively quantify these informational masking effects at both early and late stages of auditory processing using auditory evoked potentials (AEPs) in a two-factor repeated measures paradigm. Method: Thirty participants were included in this cross sectional repeated measures design. Target-masker similarity between target and masker were manipulated by varying the linguistic/phonetic similarity (i.e. language) of the talkers in the noise maskers. Specifically, four levels representing hypothesized increasing levels of informational masking were implemented: (1) No masker (quiet), (2) Mandarin (linguistically and phonetically dissimilar), (3) Dutch (linguistically dissimilar, but phonetically similar), and (4) English (linguistically and phonetically similar). Stimulus uncertainty was manipulated by task complexity, specifically target-to-target interval (TTI) of an auditory paradigm. Participants had to discriminate between English word stimuli (/bæt/ and /pæt/) presented in an oddball paradigm in each masker condition at +3 dB SNR by pressing buttons to either the target or standard stimulus (pseudo-randomized between /bæt/ and /pæt/ for all participants). Responses were recorded simultaneously for P1-N1-P2 (standard waveform) and P3 (target waveform). This design allowed for simultaneous recording of multiple AEP peaks, including analysis of amplitude, area, and latency characteristics, as well as accuracy, reaction time, and d’ behavioral discrimination to button press responses. Finally, AEP measurers were compared to performance on a behavioral word recognition task (NU-6 25-word lists) in the proposed language maskers and at multiple signal-to-noise ratios (SNRs) to further explore if AEP components of amplitude/area and latency are correlated to behavioral outcomes across proposed maskers. Results: Several trends in AEP and behavioral outcomes were consistent with the hypothesized hierarchy of increasing linguistic/phonetic similarity from Mandarin to Dutch to English, but not all differences were significant. The most supported findings for this factor were that all babble maskers significantly affected outcomes compared to quiet, and that the native language English masker had the largest effect on outcomes in the AEP paradigm, including N1 amplitude, P3 amplitude and area, as well as decreased reaction time, accuracy, and d’ behavioral discrimination to target word responses. AEP outcomes for the Mandarin and Dutch maskers, however, were not significantly different across all measured components. Outcomes for AEP latencies for both N1 and P3 also supported an effect of stimulus uncertainty, consistent with a hypothesized increase in processing time related to increased task complexity when target stimulus timing was randomized. In addition, this effect was stronger, as evidenced by larger effect sizes, at the P3 level of auditory processing compared to the N1. An unanticipated result was the absence of the expected additive effect between linguistic/phonetic similarity and stimulus uncertainty. Finally, trends in behavioral word recognition performance were generally consistent with those observed for AEP component measures such that no differences between Dutch and Mandarin maskers were found, but the English masker yielded the lowest percent correct scores. Furthermore, correlations between behavioral word recognition and AEP component measures yielded some moderate correlations, but no common AEP components accounted for a majority of variance for behavioral word recognition. Conclusions: The results of this study add to our understanding of auditory perception in informational masking in four ways. First, observable effects of both similarity and uncertainty were evidenced at both early and late levels of auditory cortical processing. This supports the use of AEPs to better understand the informational masking deficit by providing a window into the auditory pathway. Second, stronger effects were found for P3 response, an active, top-down level of auditory processing providing some suggestion that while informational masking degradation happens at lower levels, higher level active auditory processing is more sensitive to informational masking deficits. Third, the lack of interaction of main effects leads us to a linear interpretation of the interaction of similarity and uncertainty with an equal effect across listening conditions. Fourth, even though there were few and only moderate correlations to behavioral word recognition, AEP and behavioral performance data followed the same trends as AEP measures across similarity. Through both auditory neural and behavioral testing, language maskers degraded AEPs and reduced word recognition, but particularly using a native-language masker. The behavioral and objective results from this study provide a foundation for further investigation of how the linguistic content of target and masker and task difficulty contribute to difficulty understanding speech in noise

Neural Dynamics of Autistic Behaviors: Cognitive, Emotional, and Timing Substrates

What brain mechanisms underlie autism and how do they give rise to autistic behavioral symptoms? This article describes a neural model, called the iSTART model, which proposes how cognitive, emotional, timing, and motor processes may interact together to create and perpetuate autistic symptoms. These model processes were originally developed to explain data concerning how the brain controls normal behaviors. The iSTART model shows how autistic behavioral symptoms may arise from prescribed breakdowns in these brain processes.Air Force Office of Scientific Research (F49620-01-1-0397); Office of Naval Research (N00014-01-1-0624

The Effects of Aging on Lexical Access

As the U.S. population ages, the need to understand how language changes with age becomes more important. Difficulty with word retrieval is one of the most notable changes as individuals age (Burke & Shafto, 2004); however, theoretical models of aging disagree on the cause. Two prominent theories are the impaired lexical access hypothesis and the general slowing theory. The present study aimed to explore these two ideas using magnetoencephalography (MEG). A young adult group (N=17, mean age 20.6 years) and an older adult group (N=9, mean age =64.6 years) participated in a lexical decision task using verbs. MEG latency data corresponding to lexical access found no between-group difference. Behavioral response times were significantly slower in the older group. Results point either to the idea that linguistic difficulties experienced by older individuals are the result of reduced abilities in phonological or motor processing, or that while lexical representations remain intact, the connections between them become less efficient with age

Learning to perceive non-native tones via distributional training : effects of task and acoustic cue weighting

As many distributional learning (DL) studies have shown, adult listeners can achieve discrimination of a difficult non-native contrast after a short repetitive exposure to tokens falling at the extremes of that contrast. Such studies have shown using behavioural methods that a short distributional training can induce perceptual learning of vowel and consonant contrasts. However, much less is known about the neurological correlates of DL, and few studies have examined nonnative lexical tone contrasts. Here, Australian-English speakers underwent DL training on a Mandarin tone contrast using behavioural (discrimination, identification) and neural (oddball-EEG) tasks, with listeners hearing either a bimodal or a unimodal distribution. Behavioural results show that listeners learned to discriminate tones after both unimodal and bimodal training; while EEG responses revealed more learning for listeners exposed to the bimodal distribution. Thus, perceptual learning through exposure to brief sound distributions (a) extends to non-native tonal contrasts, and (b) is sensitive to task, phonetic distance, and acoustic cue-weighting. Our findings have implications for models of how auditory and phonetic constraints influence speech learning

The functional locus of emotion effects in visual word processing

Die emotionale Valenz von Wörtern beeinflusst deren kognitive Verarbeitung. Ungeklärt ist, obwohl von zentraler Bedeutung für die Disziplinen der Psycholinguistik und der Neurowissenschaften, die Frage nach dem funktionellen Lokus von Emotionseffekten in der visuellen Wortverarbeitung. In der vorliegenden Dissertation wurde mit Hilfe von Ereignis-korrelierten Potentialen (EKPs) untersucht, ob emotionale Valenz auf lexikalischen oder auf semantischen Wortverarbeitungsstufen wirksam wird. Vorausgegangene Studien weisen auf einen post-lexikalischen Lokus von Emotionseffekten hin, wobei einige wenige heterogene Befunde von sehr frühen Emotionseffekten auch einen lexikalischen Lokus vermuten lassen. In der vorliegenden Arbeit wurden drei emotions-sensitive EKP Komponenten beobachtet, die distinkte zeitliche und räumliche Verteilungen aufwiesen, und daher verschiedene Wortverarbeitungsstufen zu reflektieren scheinen. Die Ergebnisse wurden im Rahmen von allgemeinen Annahmen aktueller Wortverarbeitungs- und semantischer Repräsentationsmodelle diskutiert. Als zentrales Ergebnis kann benannt werden, dass Emotion am stärksten semantische Wortverarbeitungsstufen beeinflusste. Hieraus wurde geschlussfolgert, dass emotionale Valenz einen Teil der Wortbedeutung darstellt. Eine Interaktion mit einem lexikalischen Faktor sowie sehr frühe Emotionseffekte deuten auf einen zusätzlichen Lokus auf lexikalischen oder sogar perzeptuellen Wortverarbeitungsstufen hin. Dies bedeutet, Emotion veränderte die visuelle Wortverarbeitung auf multiplen Stufen, dabei konnten separate emotions-sensitive EKP Komponenten, die unterschiedlichen Randbedingungen unterliegen, mit jeweils einem frühen (pre-)lexikalischen und einem späten semantischen Lokus in der Wortverarbeitung in Verbindung gesetzt werden. Die Befunde stützen Wortverarbeitungsmodelle, die zeitlich flexible und interaktive Wortverarbeitungsstufen annehmen.Emotional valence of words influences their cognitive processing. The functional locus of emotion effects in the stream of visual word processing is still elusive, although it is an issue of great importance for the disciplines of psycholinguistics and neuroscience. In the present dissertation event-related potentials (ERPs) were applied to examine whether emotional valence influences visual word processing on either lexical or semantic processing stages. Previous studies argued for a post-lexical locus of emotion effects, whereas a lexical locus has been indicated by a few heterogeneous findings of very early emotion effects. Three emotion-related ERP components were observed that showed distinct temporal and topographic distributions, and thus seem to reflect different processing stages in word recognition. Results are discussed within a framework of common assumptions from word recognition and semantic representation models. As a main finding, emotion impacted most strongly semantic processing stages. Thus, emotional valence can be considered to be a part of the meaning of words. However, an interaction of emotion with a lexical factor and very early emotion effects argued for an additional functional locus on lexical, or even on perceptual processing stages in word recognition. In conclusion, emotion impacted visual word processing on multiple stages, whereas distinct emotion-related ERP components, that are subject to different boundary conditions, were associated each with an early (pre-)lexical locus or a late semantic locus. The findings are in line with models of visual word processing that assume time-flexible and interactive processing stages, and point out the need for integration of word recognition models with models of semantic representation

Exploring the Nature of Neural Correlates of Language, Attention and Memory: Reliability and Validity Studies of Event Related Potentials

Comparing data from different subfields of research may help in understanding emerging patterns and refining interpretations. This is especially true in neuroscience because brain functions can be studied at multiple levels of analysis, spatially and temporally, and with a variety of complementary measurement techniques. Within the ERP domain, several subfields of research have evolved over time, typically reflecting the specific time-window of interest and brain function investigated. The current investigation focused on three widely studied ERP effects reflecting a variety of key brain functions: the N400 effect, the P3b effect and the Left Parietal effect. The N400 effect has attracted researchers interested in language processing, the P3b effect researchers interested in attentional processes and the Left Parietal effect researchers focused on episodic recollection. Even though the ERP technology constitutes a common thread across these subfields, there is often a lack of communication across groups of researchers. The literatures on the N400 effect, P3b effect and Left Parietal effect have been written by relatively non-overlapping groups of researchers, and as such the kind of analysis carried out in the current thesis is not a common one, as it compares effects investigated within different subfields. Specifically, the approach taken in the current thesis involves assessment of the comparative reliability of the three effects of interest, and at the same time allowing refining their validity. Results showed that all three effects were found to be reliable at the group level and the N400 effect and the P3b effect were also found to be reliable at the single participant level. A correlational analysis involving all three effects yielded a significant correlation between the P3b and the Left Parietal effect but not between the P3b and the N400, or between the Left Parietal effect and the N400. Following up on the significant correlation, suggesting a convergence between the P3b effect and the Left Parietal effect, a probability manipulation of the Left Parietal effect was carried out to investigate if the old/new effect is sensitive to probability changes similarly to the P3b. The size of the Left Parietal effect was found to be sensitive to the relative probability of old and new items, in a manner consistent with the P3b effect‟s sensitivity to probability manipulations. The results pointing to a relationship between the P3b effect and the Left Parietal effect suggest that attentional processes sensitive to probability may temporally overlap and confound memory processes as indexed by the Left Parietal effect. The N400 effect, in the initial correlational study, was found to be independent from attentional processes as reflected by the P3b, and from episodic recollection as indexed by the Left Parietal effect. The validity of the N400 effect as a measure of semantic processing was then assessed by manipulating associative relationships while keeping constant semantic relationships, with results showing that the effect can be clearly modulated by associative changes when semantic relatedness is kept constant. The same association norms were then used in an old/new recognition experiment to assess if the Bilateral-Frontal old/new effect behaves in reaction to association relationships similarly or differently from the N400, in the attempt of assessing if the N400 is only a measure of associative relationships or also a measure of the process of familiarity. The observed pattern suggests independence between the N400 and the Bilateral Frontal effect. Overall, the N400 effect was found to be independent from memory processes occurring in the same time window, but, contrary to the dominant interpretation of the effect, the effect was modulated by changes in association strength while keeping semantic relatedness constant, suggesting that the N400 effect may be sensitive to a contiguity-based associative learning process not constrained to the linguistic domain