Blog Archives

Brain activity during processing objects and pseudo-objects: Comparison between adult regular and dyslexic readers

Conclusions
The results support the notion that brain activation of dyslexic readers differs from that of the regular readers when processing non-alphabetic patterns, and that the differences appear from the early stage of processing.

from Clinical Neurophysiology

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The Role of Semantic and Phonological Factors in Word Recognition: An ERP Cross-Modal Priming Study of Derivational Morphology

Theories of morphological processing differ on the issue of how lexical and grammatical information are stored and accessed. A key point of contention is whether complex forms are decomposed during recognition (e.g., establish + ment), compared to forms that cannot be analyzed into constituent morphemes (e.g., apartment). In the present study we examined these issues with respect to English derivational morphology by measuring ERP responses during a cross-modal priming lexical decision task. ERP priming effects for semantically and phonologically transparent derived words (government-govern) were compared to those of semantically opaque derived words (apartment-apart) as well as “quasi-regular” items that represent intermediate cases of morphological transparency (dresser-dress). Additional conditions independently manipulated semantic and phonological relatedness in non-derived words (semantics: couch-sofa; phonology: panel-pan). The degree of N400 ERP priming to morphological forms varied depending on the amount of semantic and phonological overlap between word types, rather than respecting a bivariate distinction between derived and opaque forms. Moreover, these effects could not be accounted for by semantic or phonological relatedness alone. The findings support the theory that morphological relatedness is graded rather than absolute, and depend on the joint contribution of form and meaning overlap.

from Neuropsychologia

The role of Broca’s area in regular past-tense morphology: An event-related potential study

It has been suggested that damage to anterior regions of the left hemisphere results in a dissociation in the perception and lexical activation of past-tense forms. Specifically, in a lexical-decision task in which past-tense primes immediately precede present-tense targets, such patients demonstrate significant priming for irregular verbs (spoke-speak), but, unlike control participants, fail to do so for regular verbs (looked-look). Here, this behavioral dissociation was first confirmed in a group of eleven patients with damage to the pars opercularis (BA 44) and pars triangularis (BA 45) of the left inferior frontal gyrus (i.e., Broca’s area). Two conditions containing word-onset orthographic-phonological overlap (bead-bee, barge-bar) demonstrated that the disrupted regular-verb priming was accompanied by, and covaried with, disrupted ortho-phonological priming, regardless of whether prime stimuli contained the regular inflectional rhyme pattern. Further, the dissociation between impaired regular-verb and preserved irregular-verb priming was shown to be continuous rather than categorical; priming for weak-irregular verbs (spent-spend) was intermediate in size between that of regular verbs and strong verbs. Such continuous dissociations grounded in ortho-phonological relationships between present- and past-tense forms are predicted by single-system, connectionist approaches to inflectional morphology and not predicted by current dual-system, rule-based models. Event-related potential data demonstrated that N400 priming effects were intact for both regular and irregular verbs, suggesting that the absence of significant regular-verb priming in the response time data did not result from a disruption of lexical access, and may have stemmed instead from post-lexical events such as covert articulation, segmentation strategies, and/or cognitive control.

from Neuropsychologia

Change and novelty detection in speech and non-speech sound streams

The aim of the present study was to determine differences in cortical processing of consonant-vowel syllables and acoustically matched non-speech sounds, as well as novel human and nonhuman sounds. Event-related potentials (ERPs) were recorded to vowel, vowel duration, consonant, syllable intensity, and frequency changes as well as corresponding changes in their non-speech counterparts with the multi-feature mismatch negativity (MMN) paradigm. Enhanced responses to linguistically relevant deviants were expected. Indeed, the vowel and frequency deviants elicited significantly larger MMNs in the speech than non-speech condition. Minimum norm source localization algorithm was applied to determine hemispheric asymmetry in the responses. Language relevant deviants (vowel, duration and – to a lesser degree – frequency) showed higher activation in the left than right hemisphere to stimuli in the speech condition. Novel sounds elicited novelty P3 waves, the amplitude of which for nonhuman sounds was larger in the speech than non-speech condition. The current MMN results imply enhanced processing of linguistically relevant information at the pre-attentive stage and in this way support the domain-specific model of speech perception.

from Brain Research

Alterations in Event Related Potentials (ERP) Associated with Tinnitus Distress and Attention

from Applied Psychophysiology and Biofeedback

Abstract Tinnitus related distress corresponds to different degrees of attention paid to the tinnitus. Shifting attention to a signal other than the tinnitus is therefore particularly difficult for patients with high tinnitus related distress. As attention effects on Event Related Potentials (ERP) have been shown this should be reflected in ERP measurements (N100, phase locking). In order to prove this hypothesis single sweep ERP recordings were obtained in 41 tinnitus patients as well as 10 control subjects during a period of time when attention was shifted to a tone (attended) and during a second phase (unattended) when they did not focus attention to the tone. Whereas tinnitus patients with low distress showed a significant reduction in both N100 amplitude and phase locking when comparing the attended and unattended measurement condition a group of patients with high tinnitus related distress did not show such ERP alterations. Using single sweep ERP measurements the results of our study show, that attention in high tinnitus related distress patients is captured by their tinnitus significantly more than in low distress patients. Furthermore our results provide the basis for future neurofeedback based tinnitus therapies aiming at maximizing the ability to shift attention away from the tinnitus.

An error-detection mechanism in reading among dyslexic and regular readers – An ERP study

from Clinical Neurophysiology

Objective
As a continuation of a previous study which demonstrated the existence of the error-monitoring mechanism among regular readers, the current study attempts to characterize the error detection negativity (ERN/Ne) and the correct-related negativity (CRN) among dyslexics. More specifically, given the lexical and semantic processes involved in reading, the study attempts to reveal the reasons for differences between regular and dyslexic readers with respect to the ERN/Ne and N400 amplitudes and latencies.

Methods
A visual lexical decision paradigm and event-related potential (ERP) analysis were used.

Results
Dyslexics exhibited lower ERN/Ne amplitudes and later latencies in error responses as compared to correct responses. A smaller difference between the ERN/Ne and CRN amplitudes among dyslexics was observed. In addition, a later N400 component was elicited for error responses in both groups of readers.

Conclusion
A different error-detection activity level among dyslexic readers was found in reading.

Significance
These results emphasize the differences in brain activity among regular and dyslexic readers. Our results point at a possible model of brain processing of incorrect reading among dyslexics. This model can be used to explain the reasons for repeated reading errors among adult compensated dyslexics despite extensive exposure to print over the years.