Copy to URL Repository Edition
- Attentional modulation of oscillatory neuronal synchrony in the beta band as a neural correlate of response selection (Jasper Poort)
- Lateralized activation of the motor system to the observation of left and right hand actions (Thomas Koelewijn)
- L2-L1 Word Association in Bilinguals: Direct Evidence (Laura Menenti)
- Bilingual word representation: a multi-task fMRI investigation (Laura Menenti)
- Distinguishing between prelexical levels in speech perception: an adaptation-fMRI study (Attila Andics)
Abstract
Oscillatory neuronal synchrony is thought to play an essential role in the neuronal processing of information. We argue that attention can selectively bias processing by modulation of these ongoing oscillations. This allows active instead of mere reactive responses to sensory stimulation or feedforward activation. Here we present evidence for the functional role of oscillatory neuronal synchronization in attention obtained with magnetoencephalography. Subjects performed a bilateral isometric contraction and were cued in some trials to respond at the event of the imperative go-cue with a left and in others with a right wrist extension. The analysis of the period in which subjects were waiting for the go-cue (stimulation period) revealed that beta power (15-30 Hz) over motor cortex was reliably related to response selection. Beta power was lower over motor cortex when it was contralateral to the expected response side compared to when it was contralateral to the side of which no response was required. This difference did not exist in the baseline period in which the go-cue could not occur. The effect was due to a decrease in beta power in the stimulation period compared to baseline that was bigger for the motor cortex driving the cued side. Importantly, it was not time-locked to response onset since subjects knew not if and when the go-cue would occur and therefore reflected expectation rather than preparation of a motor response. Force output was equal in the two conditions and stratification of the EMG signals did not change the results. The location of the maximal cortico-muscular coherence in an independent data set was highly similar to the location of the maximal beta lateralization, and analysis within these channels also showed the same results. We conclude that these results show selective modulation of beta power by attention and that this modulation is a neural correlate of response selection.
Keywords; attention; oscillatory synchrony; response selection; MEG; EMG;
Abstract
A primary feature of the human motor system is its crossed organization (e.g. left motor cortex controls right hand). In the present study MEG recordings were used to investigate whether observation of left and right hand finger movement results in lateralized activation of the motor cortex. Lateralized activation in the form of a lateralized readiness field was found over the motor cortex for both executed and observed finger movements. These results suggest that the basic neural organization that controls left and right limb movements during execution may be used to effectively differentiate between left and right movements of others in action observation.
Abstract
The Revised Hierarchical Model (Kroll and Stewart, 1994) assumes that words in a bilingual’s languages have separate word form representations but shared conceptual representations. Two routes lead from an L2 word form to its conceptual representation: the word association route, where concepts are accessed through the corresponding L1 word form, and the concept mediation route, with direct access from L2 to concepts. To investigate word association, we presented proficient late German-Dutch bilinguals with L2 non-cognate word pairs in which the L1 translation of the first word rhymed with the second word (e.g. GRAP (joke) – Witz – FIETS (bike)). If the first word in a pair activated its L1 equivalent, then a phonological priming effect on the second word was expected. Priming was observed in lexical decision but not in semantic decision (living/non-living) on L2 words. In a control group of Dutch native speakers, no priming effect was found. This suggests that proficient bilinguals still make use of their L1 word form lexicon to process L2 in lexical decision.
Abstract
The Revised Hierarchical Model (Kroll and Stewart, 1994) assumes that words in a bilingual’s languages have separate word form representations but shared conceptual representations. Two routes lead from an L2 word form to its conceptual representation: the word association route, where concepts are accessed through the corresponding L1 word form, and the concept mediation route, with direct access from L2 to concepts. The implications of the RHM for fMRI data were investigated. Proficient German-Dutch bilinguals carried out three tasks (voice decision, lexical decision and semantic decision) in their L1 and L2. LIFG and the left superior temporal gyrus were among the many areas responding more strongly to L2 than L1, while the right middle temporal gyrus was the only area responding more strongly to L1. Data from a previous behavioral experiment suggest that word association takes place in lexical but not semantic decision. An interaction between task and language was therefore expected in an area that processes L1 word forms. In a volume-of-interest analysis, such an area was found in the right posterior middle temporal gyrus. This area may therefore be involved in processing L1 word forms, in particular in the L1 processing that serves word association from L2.
Abstract
Behavioural studies of speech perception indicate a dissociation of acoustic-phonetic and a more abstract level of prelexical processing. Here we used functional magnetic resonance imaging, in combination with an adaptation paradigm to distinguish between the neural correlates of acoustic-phonetic and phonological processing of the fricative speech sounds [S] and [s] by Dutch listeners. To manipulate the perceived quality of the fricatives while keeping their acoustic properties constant, we varied the sounds’ vowel-context: Dutch listeners are more likely to classify an ambiguous fricative from an [S] – [s] continuum as [S] when it is followed by [i], and as [s] when it is followed by [y] (Smits, 2001a). Syllable pairs were presented consisting of an [S], an [s], or an ambiguous fricative, followed by an [y] or an [i] vowel. The most ambiguous fricative was identified individually for each subject in a pretest. During the fMRI scanning session syllable pairs were presented rapidly, randomly intermixed. A sparse scanning paradigm was used, in which auditory stimuli were presented during silent gaps between image acquisitions. We hypothesized that syllable pairs in which the fricatives were perceived as the same would lead to larger adaptation in brain regions responsible for phonological processing as compared to syllable pairs in which the fricatives were perceived as different. Distinct fMRI adaptation patterns were observed corresponding to acoustic-phonetic and phonological processing respectively, supporting the functional distinction between these processing levels. No cortical regions showed both patterns: the cortical regions underlying the acoustic-phonetic and phonological stages in prelexical processing appear to be anatomically distinct.