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  • The EEG Signature of Same Words Spoken by Different Speakers S. Elahi, Professor J. Brennan

    Department of LinguisBcs at the University of Michigan

    Results A: n1 early stages of acousBc processing possible acousBc priming for same talk B: p2 later stages of acousBc processing lack of acousBc priming for diff talker C: n400 semanBc processing lack of semanBc priming for non repeated words

    n400 semanBc processing reduced for both repeBBon condiBons D: possible p300 unexpected sBmuli processing with diff talker

    Conclusion PaMerns we see at this point and Bme: repeBBon effects for the same talker appear earlier, ~100 milliseconds repeBBon effects for different talkers do not appear later, >300 milliseconds

    S4muli Condi4ons and Hypothesized Priming Effect R: repeat; NR: non-repeat; +: feature is repeated in sBmuli pair; : feature is not repeated in sBmuli pair

    Data CollecBon

    Materials

    Experiment

    ParBcipants

    Our study obtained data from X parBcipants: each subject was right-handed, learned English as his or her first language, and possessed no severe neurological impairments or disorders. Sessions lasted for an hour and a half

    and all took place in the ComputaBonal NeurolinguisBcs Lab in Lorch Hall.

    Methods

    Introduc4on Hearing a word affects an individuals understanding of the word that follows. For example, if one was to hear dog, a repeated uMerance dog would be processed quicker than another word. Priming effects occur at each linguisBc level of speech percepBon-acousBcally, phoneBcally, phonologically, lexically, and conceptually.

    Furthermore, we understand a given word with apparent effortlessness even when spoken by different speakers. Though the semanBcs of a given word remains the same, the phoneBc and acousBc aspect of the word varies with speaker yet we are sBll able to understand that dog means dog.

    At issue is how we recognize words given acousBc and phoneBc variaBon. The prototype theory states that we possess the same mental representaBon for a given object and compare any new sBmuli of that object to a single prototype we have constructed in our head. AlternaBvely, the exemplar theory proposes that we categorize objects by comparison of any new sBmuli with instances of that word we have stored in memory.

    Recent research indicates that more rapid processing occurs when the same word is repeated by the same speaker as opposed to when it is repeated by different speakers. We use electroencephalography (EEG) to record charges in scalp electrical potenBals caused by neural acBvity while the parBcipants perform an experiment regarding this effect. We compare the Bme-course of Event-Related Poten4als (ERP) between condiBons to test for what stage of processing is being primed.

    Word Non-Word Same

    Speaker Different Speaker

    Same Speaker

    Different Speaker

    R NR R NR R NR R NR Acous4cs + (+) + (+) Phone4cs + () + () Phonology + + + + Seman4cs + +

    We used electroencephalography (EEG) to record electrical acBvity in the brain. We situated each subject in a nylon cap containing 61 acBvely amplified electrodes evenly distributed across the scalp. These electrodes measured electrical potenBal, which reflected the current generated

    by the summary of corBcal neurons in the brain.

    We injected electrolyte gel to minimize impedance

    while it is being monitored. Low impedances means the

    electrical connecBon between the skin and

    electrode are stabilized.

    Hearing threshold was idenBfied for each subject using a 1000 Hz tone. The volume was set to be 45 dB above this

    threshold.

    The task of the parBcipants was to iden4fy if the s4mulus was a word or a non-word as quickly and accurately as possible. This

    indicaBon was made by pressing either the lei or right buMon on a gamepad console. Subjects were presented with a total of 700

    words, separated into secBons containing 50 words each. Each word was separated from each other by an inter-sBmulus interval that

    ranged from 400 -600 milliseconds. The image to the lei depicts the brain signals we monitor during the experiment.

    Abstract Speech percepBon research shows that individuals with normal language processing rapidly understand the meaning of a spoken word despite the fact the arBculaBon and acousBcs of these words differ - someBmes significantly - across speakers of the same dialect. While the semanBcs of the word spoken by two separate speakers would remain the same, the phonology, phoneBcs, and acousBcs of the word are different among the two. In order to contribute to the mapping of this capacity for "speech normalizaBon", we test the Bming of repeBBon effects within and across speakers using electroencephalography. This allows us to idenBfy the Bming of cogniBve processes that allow the brain to recognize that the same word uMered by two different speakers are, in fact, the same word. We used electroencephalography (EEG) to record charges in electrical potenBals that are caused by neural acBvity while the human subjects listened to: words or non-words, either repeated or no repeated, and if repeated, by the same speaker or by different speakers. The results from this experiment will indicate how quickly we recognize two words (that are the same) are the same

    Experimental Design

    No rep

    grassx dogA catA boMlex

    Diff talk

    grassx dogA dogB boMlex

    Same talk

    grassx dogA dogA boMlex

    Hypothesis and Objec4ves Our objecBve is to discover at what point in 4me is the difference in acous4cs and phone4cs of repeated words, spoken by different speakers, factored out seman4c aUribute of the word manifests within our minds. We do this by looking for what brain signals were sensiBve when words were repeated (either by the same speaker or by different speakers) compared to when they were not repeated. We predict that early components will be reduced for within-speaker priming due to repeBBon effects on acousBc and/or phoneBc processing. In contrast, we predict that between-speaker priming will only show aMenuaBon on later components, reflecBng lexical and/or conceptual priming.