Audiovisual perception of natural speech is impaired in adult dyslexics: an ERP study.

The present study used event-related brain potentials (ERPs) to investigate audiovisual integration processes in the perception of natural speech in a group of German adult developmental dyslexic readers. Twelve dyslexic and twelve non-dyslexic adults viewed short videos of a male German speaker. Disyllabic German nouns served as stimulus material. The auditory and the visual stimulus streams were segregated to create four conditions: in the congruent condition, the spoken word and the auditory word were identical. In the incongruent condition, the auditory and the visual word (i.e., the lip movements of the utterance) were different. Furthermore, on half of the trials, white noise (45 dB SPL) was superimposed on the auditory trace. Subjects had to say aloud the word they understood after they viewed the video. Behavioral data. Dyslexic readers committed more errors compared to normal readers in the noise conditions, and this effect was particularly present for congruent trials. ERPs showed a distinct N170 component at temporo-parietal electrodes that was smaller in amplitude for dyslexic readers. Both, normal and dyslexic readers, showed a clear effect of noise at centro-parietal electrodes between 300 and 600 ms. An analysis of error trials reflecting audiovisual integration (verbal responses in the incongruent noise condition that are a mix of the visual and the auditory word) revealed more positive ERPs for dyslexic readers at temporo-parietal electrodes 200-500 ms poststimulus. For normal readers, no such effect was present. These findings are discussed as reflecting increased effort in dyslexics under circumstances of distorted acoustic input. The superimposition of noise leads dyslexics to rely more on the integration of auditory and visual input (lip reading). Furthermore, the smaller N170-amplitudes indicate deficits in the processing of moving faces in dyslexic adults.

Developmental dyslexics show altered allocation of attention in visual classification tasks.

OBJECTIVES: Event-related brain potentials (ERPs) were recorded to investigate allocation of attention in adult developmental dyslexics. SUBJECTS AND METHODS: Twelve adult developmental dyslexics and 12 matched normal controls performed three visual choice reaction tasks. In the passive oddball condition, subjects watched two different simple visual stimuli presented with 87.5 and 12.5% probability. In the active oddball condition, participants responded to the low-probability target stimulus. In the active 50/50-condition, both stimuli were presented with 50% probability and a response was required to the target stimulus only. RESULTS: No group differences emerged for performance, P300 latency or laterality and for N200 amplitude, latency or laterality. An enhancement of P300 amplitude with a frontal distribution was found for NoGo (standard)-stimuli in both active conditions for the dyslexic sample. CONCLUSION: Results are discussed in the context of deviances in allocation of attentional resources in dyslexic readers.

Event-related brain potentials to sound omissions differ in musicians and non-musicians.

The mismatch negativity (MMN) component of the auditory event-related brain potential reflects the automatic detection of sound change. MMN to occasionally omitted sounds in a tone series can be used to investigate the time course of temporal integration in the acoustic system. We used MMN to study differences in temporal integration in musicians and non-musicians. In experiment 1, occasionally omitted 'sounds' in an otherwise regular tone series evoked a reliable MMN at interstimulus intervals (SOAs) of 100, 120, 180 and 220 ms in musicians. In non-musicians, MMN was smaller/absent in the 180 and 220 ms SOAs, respectively. In experiment 2, deviance of a tone was induced by presenting tones at a shorter SOA (100 or 130 ms) compared to the standard stimulus (150 ms). Musicians showed a reliable MMN for both deviant SOAs whereas non-musicians showed an MMN only for tones presented 50 ms prior to a standard tone (SOA 100 ms). These results indicate that the temporal window of integration seems to be longer and more precise in musicians compared to musical laypersons and that long-term training is reflected in changes in neural activity.

Implicit and explicit learning of event sequences: evidence for distinct coding of perceptual and motor representations.

Event-related brain potentials (ERPs) of 21 subjects were recorded in a choice reaction time task with a repeating eight-element long stimulus sequence. The regular event sequence was sometimes interrupted by 'perceptual' or by 'motor deviants' which both replaced an expected stimulus but either preserved or violated the sequence of motor responses. Response times confirmed that all subjects had acquired some knowledge of the sequential dependencies. By means of a post-experimental free recall and recognition test, subjects were classified as having either explicit or implicit knowledge of the event sequence. The ERPs showed different effects for different types of stimuli and the two groups. In the group of explicit learners, a larger N200 component was evoked by both types of deviants and a larger P300 by motor deviants only. In the group of implicit learners these 'perceptual components' remained unaffected. In contrast, in both groups of subjects the lateralized readiness potential (LRP) which accompanied motor deviants revealed a partial activation of the to be expected but incorrect response, i.e. motor learning. These results suggest that explicit learners acquire knowledge about both, stimulus and response dependencies while implicit learners acquire knowledge about response dependencies only.

[Memory traces in EEG]. / Gedächtnisspuren im EEG.

The paper gives a brief overview of five experimental approaches in which memory processes were studied by means of event-related brain potentials (ERPs). Some of the results were already published in English (Study 1), while others are new and will be reported in greater length as full paper elsewhere (Studies 2, 3, 4, and 5). Study 1 revealed that retrieval of information from episodic long-term memory is accompanied by a systematic slow negative potential. The topography of this slow wave depends on the quality of the reactivated information (spatial vs. verbal), and its amplitude reflects the difficulty of the retrieval process. In experiment 2 ERPs were recorded while subjects acquired either explicit or implicit knowledge about a sequential stimulus-response pattern. The data suggest that explicit learners who posses verbalizable knowledge about sequential dependencies have formed both perceptual and motor representations, while implicit learners have formed motor representations only. In study 3 fact retrieval in mental arithmetic was activated by a verification task. Incongruent solutions evoked an arithmetic N400-effect whose amplitude varied with the associative distance between an expected and an actually perceived solution to a multiplication problem. In study 4 ERPs were recorded during mental rotation tasks. A set of experiments revealed that mental rotation is always accompanied by a systematic negative variation over the parietal cortex. The amplitude of this "rotation specific negativity" increases with an increasing angular disparity between a perceived sign and its normal upright template. It was shown that this negativity is functionally distinct from a P300-complex which is often superimposed on it within the same latency window. Finally, study 5 examined ERPs in a sentence reading task in which grammatically legal but infrequent sentence constructions had to be processed. A left-anterior negativity was observed whenever an explicit case marker (the definite article in German) signalled a nominal phrase at a noncanonical position. The LAN phenomenon appears to be a manifestation of a syntax processor which performes a first-pass formal analysis of a sentence and which possibly allocates working memory resources whenever a word cannot be assigned immediately to an expected propositional role.