Explicit processing of verbal and spatial features during letter-location binding modulates oscillatory activity of a fronto-parietal network.

The present study investigated the binding of verbal and spatial features in immediate memory. In a recent study, we demonstrated incidental and asymmetrical letter-location binding effects when participants attended to letter features (but not when they attended to location features) that were associated with greater oscillatory activity over prefrontal and posterior regions during the retention period. We were interested to investigate whether the patterns of brain activity associated with the incidental binding of letters and locations observed when only the verbal feature is attended differ from those reflecting the binding resulting from the controlled/explicit processing of both verbal and spatial features. To achieve this, neural activity was recorded using magnetoencephalography (MEG) while participants performed two working memory tasks. Both tasks were identical in terms of their perceptual characteristics and only differed with respect to the task instructions. One of the tasks required participants to process both letters and locations. In the other, participants were instructed to memorize only the letters, regardless of their location. Time–frequency representation of MEG data based on the wavelet transform of the signals was calculated on a single trial basis during the maintenance period of both tasks. Critically, despite equivalent behavioural binding effects in both tasks, single and dual feature encoding relied on different neuroanatomical and neural oscillatory correlates. We propose that enhanced activation of an anterior–posterior dorsal network observed in the task requiring the processing of both features reflects the necessity for allocating greater resources to intentionally process verbal and spatial features in this task

Word Processing differences between dyslexic and control children

BACKGROUND: The aim of this study was to investigate brain responses triggered by different wordclasses in dyslexic and control children. The majority of dyslexic children have difficulties to phonologically assemble a word from sublexical parts following grapheme-to-phoneme correspondences. Therefore, we hypothesised that dyslexic children should mainly differ from controls processing low frequent words that are unfamiliar to the reader. METHODS: We presented different wordclasses (high and low frequent words, pseudowords) in a rapid serial visual word (RSVP) design and performed wavelet analysis on the evoked activity. RESULTS: Dyslexic children had lower evoked power amplitudes and a higher spectral frequency for low frequent words compared to control children. No group differences were found for high frequent words and pseudowords. Control children had higher evoked power amplitudes and a lower spectral frequency for low frequent words compared to high frequent words and pseudowords. This pattern was not present in the dyslexic group. CONCLUSION: Dyslexic children differed from control children only in their brain responses to low frequent words while showing no modulated brain activity in response to the three word types. This might support the hypothesis that dyslexic children are selectively impaired reading words that require sublexical processing. However, the lacking differences between word types raise the question if dyslexic children were able to process the words presented in rapid serial fashion in an adequate way. Therefore the present results should only be interpreted as evidence for a specific sublexical processing deficit with caution

Influence of Stimulus Distance in Implicit Learning of Spatial and Nonspatial Event Sequences

The serial reaction time task has been widely used to investigate implicit learning mechanisms. In the present study, we investigated the effect of stimulus distance on learning of a spatial sequence independent of a sequence of responses. Participants had to respond to objects appearing at four different locations. The objects were presented in a sequence of nine elements, whereas the location at which an object was presented followed a sequence of eight elements. Thus, the spatial and the object sequences were independent of each other. Four groups of subjects for whom the distances of the locations chosen to present objects on the computer screen (3 cm, 6 cm, 12 cm, or 22 cm) differed were tested. Only the nonspatial sequence was learned as indicated by enhanced response latencies in nonsequenced random blocks. Stimulus distance had no effect on the amount of sequence learning. Additional analyses for subgroups of subjects who did not show explicit knowledge of the sequences after completion of the task indicated that for implicit learners also, sequence learning was not influenced by stimulus distance. The results are discussed with respect to current theories of implicit serial learning. </jats:p

Mental rotation of letters, pictures, and three-dimensional objects in German dyslexic children

This study examines mental rotation ability in children with developmental dyslexia. Prior investigations have yielded equivocal results that might be due to differences in stimulus material and testing formats employed. Whereas some investigators found dyslexic readers to be impaired in mental rotation, others did not report any performance differences or even superior spatial performance for dyslexia. Here, we report a comparison of mental rotation for letters, three-dimensional figures sensu Shepard and Metzler, and colored pictures of animals or humans in second-grade German dyslexic readers. Findings indicate that dyslexic readers are impaired in mental rotation for all three kinds of stimuli. Effects of general intelligence were controlled. Furthermore, dyslexic children were deficient in other spatial abilities like identifying letters or forms among distracters. These results are discussed with respect to the hypotheses of a developmental dysfunction of the parietal cortex or a subtle anomaly in cerebellar function in dyslexic readers

Does EEG activity during painful stimulation mirror more closely the noxious stimulus intensity or the subjective pain sensation?

Background: Many researchers have tried to investigate pain by studying brain responses. One method used to investigate pain-related brain responses is continuous electroencephalography (EEG). The objective of the current study is to add on to our understanding of EEG responses during pain, by differentiation between EEG patterns indicative of (i) the noxious stimulus intensity and (ii) the subjective pain sensation. Methods: EEG was recorded during the administration of tonic experimental pain, consisting of six minutes of contact heat applied to the leg via a thermode. Two stimuli above pain threshold, one at pain threshold and two non-painful stimuli were administered. Thirty-six healthy participants provided a subjective pain rating during thermal stimulation. Relative EEG power was calculated for the frequency bands alpha1, alpha2, beta1, beta2, delta, and theta. Results: Whereas EEG activity could not be predicted by stimulus intensity (except in one frequency band), subjective pain sensation could significantly predict differences in EEG activity in several frequency bands. An increase in the subjective pain sensation was associated with a decrease in alpha2, beta1, beta2 as well as in theta activity across the midline electrodes. Conclusion: The subjective experience of pain seems to capture unique variance in EEG activity above and beyond what is captured by noxious stimulus intensity

Developmental Dyslexia and implicit learning: Evidence from an AGL transfer study

AbstractImplicit learning was explored in typical and developmental dyslexic children using the AGL paradigm (Reber, 1967). Two experiments were conducted; Experiment 1: non-transfer condition and Experiment 2: transfer condition. Typical children showed intact implicit learning under both conditions and transfer of knowledge. Children with developmental dyslexia on the other hand, were found impaired under both experimental conditions. It is argued that dyslexic children may face problems with implicit abstraction. The educational implications of the current results are discussed in relation to the prevalent teaching strategies in developmental dyslexia