Biomedical subjects

Frank Rösler

Publications and source records attributed to Frank Rösler.

At least 19 recordsLinked to original sources

PubMed2006

Reduced EEG alpha activity over parieto-occipital brain areas in congenitally blind adults.

OBJECTIVE: Goal of the present study was to compare the amplitude and topography of EEG alpha activity between congenitally blind and sighted adults both in a primarily sensory and a primarily cognitive task. METHODS: Congenitally blind and blindfolded sighted adults performed a somatosensory perception task (experiment 1), which required to discriminate tactile stimuli at different fingers, and a mental imagery task (experiment 2), in which a previously haptically encoded map had to be mentally scanned. The EEG was recorded with 61 electrodes and was analyzed with the Fast Fourier Transformation (FFT). RESULTS: Results showed a significant reduction of alpha power in the blind compared to the sighted controls over parieto-occipital recording sites in both tasks. CONCLUSIONS: It is speculated that brain structures, which have been associated with the generation of posterior alpha rhythms in sighted adults, including the geniculo-cortical pathway, depend on visual input and might either be reorganized or atrophied following blindness from birth. SIGNIFICANCE: The present study demonstrates that oscillatory activity of the brain might serve as a marker of cortical reorganization.

Adult↗

PubMed2006

Tight covariation of BOLD signal changes and slow ERPs in the parietal cortex in a parametric spatial imagery task with haptic acquisition.

The present study investigated the relation of brain activity patterns measured with functional magnetic resonance imaging (fMRI) and slow event-related potentials (ERPs) associated with a complex cognitive task. A second goal was to examine the neural correlates of spatial imagery of haptically--instead of visually--acquired representations. Using a mental image scanning task, spatial imagery requirements were systematically manipulated by parametrically varying the distance between haptically acquired landmarks. Results showed a close relation between slow ERPs and the blood oxygenation level dependent (BOLD) signal in human parietal lobe. Reaction times of mental scanning correlated with the distances between landmarks on the learned display. In parallel, duration and amplitude of slow ERPs and duration of the haemodynamic response systematically varied as a function of mental scanning distance. Source analysis confirmed that the ERP imagery effect likely originated from the same cortical substrate as the corresponding BOLD effect. This covariation of the BOLD signal with slow ERPs is in line with recent findings in animals demonstrating a tight link between local field potentials and the BOLD signal. The parietal location of the imagery effect is consistent with the idea that externally triggered (perceptual) and mentally driven (imagery) spatial processes are both mediated by the same supramodal brain areas.

Acoustic Stimulation↗

PubMed2005

Content-specific activation during associative long-term memory retrieval.

We tested whether visual stimulus material that is assumed to be processed in different cortical networks during perception (i.e., faces and spatial positions) is also topographically dissociable during long-term memory recall. With an extensive overlearning procedure, 12 participants learned paired associates of words and faces and words and spatial positions. Each word was combined with either one or two positions or one or two faces. fMRI was recorded several days later during a cued recall test, in which two words were presented and the participants had to decide whether these were linked to each other via a common mediator, i.e., a face or a position. This paradigm enforces retrieval from long-term memory without confounding recall with perceptual processes. A network of cortical areas was found to be differently activated during recall of positions and faces, including regions along the dorsal and ventral visual pathways, such as the parietal and precentral cortex for positions and the left prefrontal, temporal (including fusiform gyrus) and posterior cingulate cortex for faces. In a subset of these areas, the BOLD response was found to increase monotonically with the number of the to-be-re-activated associations. These results show that material-specific cortical networks are systematically activated during long-term memory retrieval that overlap with areas also activated by positions and faces during perceptual and working memory tasks.

Adult↗

PubMed2005

Material-specific long-term memory representations of faces and spatial positions: evidence from slow event-related brain potentials.

Motivated by models that propose material-specific cortical long-term memory representations we expected different topographies of event-related slow waves of the EEG during cued retrieval of two distinct types of information (faces and spatial positions), which are assumed to be processed and stored in topographically distinct cortical areas, i.e., in either the ventral or the dorsal visual pathway. Seventeen participants learned associations either between words and spatial positions or between words and faces. Each word was associated with either one or two positions or faces. In a cued recall test, one day later, participants saw two words and had to decide whether these were linked to each other via an associated spatial position or a face. Slow event-related potentials (ERPs) of the EEG were recorded from 61 scalp electrodes during both acquisition and recall. Response times increased monotonically with the number of faces and positions to be reactivated. Negative slow ERPs showed a comparable topography during anticipation learning and cued recall, but dissociated topographically for positions and faces. The maximum of the negativity increased when items were presented repetitively (compared to the first presentation) during learning, and also with the number of the to-be-reactivated associations during retrieval. These results are consistent with an information-processing model that assumes material-specific cortical representations of episodic memory contents, which are established as localized cortical cell assemblies during encoding, and which are being reactivated during recall.

Adult↗

PubMed2005

From single-channel recordings to brain-mapping devices: the impact of electroencephalography on experimental psychology.

Since its discovery in 1920, the electroencephalogram (EEG) has become a widely used tool in experimental psychology. Although originally the merits of the method were seen first of all in an improvement of medical diagnostics it was soon understood by psychologists that EEG can also be used to study psychic processes in healthy participants. This article summarizes important events in the history of EEG research that laid the ground for this development, as fast Fourier transformation to analyze the spontaneous activity and signal averaging to improve the signal-to-noise ratio. The article shows how general technological developments were the prerequisite for these methodological improvements in EEG research and how they inspired new research questions. Key discoveries that proved unequivocally that psychic processes do become manifest in EEG signals are briefly reviewed, and the emerging paradigm of cognitive psychophysiology, which is closely linked to the development of EEG research, is described.

Electroencephalography↗

PubMed2005

Multisensory processing in the redundant-target effect: a behavioral and event-related potential study.

Participants respond more quickly to two simultaneously presented target stimuli of two different modalities (redundant targets) than would be predicted from their reaction times to the unimodal targets. To examine the neural correlates of this redundant-target effect, event-related potentials (ERPs) were recorded to auditory, visual, and bimodal standard and target stimuli presented at two locations (left and right of central fixation). Bimodal stimuli were combinations of two standards, two targets, or a standard and a target, presented either from the same or from different locations. Responses generally were faster for bimodal stimuli than for unimodal stimuli and were faster for spatially congruent than for spatially incongruent bimodal events. ERPs to spatially congruent and spatially incongruent bimodal stimuli started to differ over the parietal cortex as early as 160 msec after stimulus onset. The present study suggests that hearing and seeing interact at sensory-processing stages by matching spatial information across modalities.

Adult↗

PubMed2004

Altered auditory-tactile interactions in congenitally blind humans: an event-related potential study.

It has been shown that stimuli of a task-irrelevant modality receive enhanced processing when they are presented at an attended location in space (crossmodal attention). The present study investigated the effects of visual deprivation on the interaction of the intact sensory systems. Random streams of tactile and auditory stimuli were presented at the left or right index finger of congenitally blind participants. They had to attend to one modality (auditory or tactile) of one side (left or right) and had to respond to deviant stimuli of the attended modality and side. While in a group of sighted participants, early event-related potentials (ERPs) were negatively displaced to stimuli presented at the attended position, compared to the unattended, for both the task-relevant and the task-irrelevant modality, starting as early as 80 ms after stimulus onset (unimodal and crossmodal spatial attention effects, respectively), corresponding crossmodal effects could not be detected in the blind. In the sighted, spatial attention effects after 200 ms were only significant for the task-relevant modality, whereas a crossmodal effect for this late time window was observed in the blind. This positive rather than negative effect possibly indicates an active suppression of task-irrelevant stimuli at an attended location in space. The present data suggest that developmental visual input is essential for the use of space to integrate input of the non-visual modalities, possibly because of its high spatial resolution. Alternatively, enhanced perceptual skills of the blind within the intact modalities may result in reduced multisensory interactions ("inverse effectiveness of multisensory integration").

Acoustic Stimulation↗

PubMed2004

Early vision impairs tactile perception in the blind.

Researchers have known for more than a century that crossing the hands can impair both tactile perception and the execution of appropriate finger movements. Sighted people find it more difficult to judge the temporal order when two tactile stimuli, one applied to either hand, are presented and their hands are crossed over the midline as compared to when they adopt a more typical uncrossed-hands posture. It has been argued that because of the dominant role of vision in motor planning and execution, tactile stimuli are remapped into externally defined coordinates (predominantly determined by visual inputs) that takes longer to achieve when external and body-centered codes (determined primarily by somatosensory/proprioceptive inputs) are in conflict and that involves both multisensory parietal and visual cortex. Here, we show that the performance of late, but not of congenitally, blind people was impaired by crossing the hands. Moreover, we provide the first empirical evidence for superior temporal order judgments (TOJs) for tactile stimuli in the congenitally blind. These findings suggest a critical role of childhood vision in modulating the perception of touch that may arise from the emergence of specific crossmodal links during development.

Adolescent↗

PubMed2004

EEG power and coherence analysis of visually presented nouns and verbs reveals left frontal processing differences.

Spectral power and coherence of the electroencephalogram was measured while subjects read either a verb or a noun which initiated a short meaningful phrase. For both types of words theta-power decreased substantially relative to a prestimulus baseline at left anterior electrode sites. All other frequency bands showed less (alpha, beta) or no effects at all (gamma). The theta-power attenuation was more pronounced for verbs than for nouns, thus indicating a stronger desynchronization for verbs at left frontal sites. Coherence of the theta-band revealed that these left anterior electrodes became decoupled from left and right posterior sites, again more for verbs than for nouns. These spectral changes are assumed to reflect processing differences due to the grammatical status of the two word categories.

Adult↗

PubMed2004

Facts, rules, and strategies in single-digit multiplication: evidence from event-related brain potentials.

It has been hypothesized that zero vs. nonzero operands in single-digit multiplication problems invoke distinct solution strategies. We studied such problems in an implicit production task with event-related brain potentials (ERPs) recorded from 61 scalp positions in 18 participants. The topography of a slow negative wave, which accompanied the implicit production of the multiplication result, varied with problem type. In comparison to small problems, larger problems evoked a stronger negativity over fronto-central and right temporal sites, and zero problems evoked a left anterior negativity. These topographic differences indicate not only that zero and small nonzero problems are solved by means of distinct strategies-most likely rule application vs. fact retrieval-but also that larger, less practiced problems invoke other processes than pure fact retrieval. Moreover, ERPs showed a positive deflection around 450 ms with a centro-parietal topography (P300), whose amplitude reflected differences in anticipated problem difficulty.

Adolescent↗

PubMed2004

The effects of late acquisition of L2 and the consequences of immigration on L1 for semantic and morpho-syntactic language aspects.

It has been hypothesized that some aspects of a second language (L2) might be learned easier than others if a language is learned late. On the other hand, non-use might result in a loss of language skills in one's native, i.e. one's first language (L1) (language attrition). To study which, if any, aspects of language are affected by either late acquisition or non-use, long-term German immigrants to the US and English native speakers who are long-term immigrants to Germany as well as two additional control groups of native German speakers were tested with an auditory semantic and morpho-syntactic priming paradigm. German adjectives correctly or incorrectly inflected for gender and semantically associated or not associated with the target noun served as primes. Participants made a lexical decision on the target word. All groups of native German speakers gained from semantically and morpho-syntactically congruent primes. Evidence for language attrition was neither found for semantic nor morpho-syntactic priming effects in the German immigrants. In contrast, English native speakers did not gain from a morpho-syntactic congruent prime, whereas semantic priming effects were similar as for the remaining groups. The present data suggest that the full acquisition of at least some syntactic functions may be restricted to limited periods in life while semantic and morpho-syntactic functions seem to be relatively inured to loss due to non-use.

Adult↗

PubMed2004

Visuospatial attention: how to measure effects of infrequent, unattended events in a blocked stimulus design.

This fMRI study investigates the differences between a blocked and event-related analysis in a cued target detection task, the so-called Posner paradigm, using a hybrid design. Validly and invalidly cued trials were presented intermingled in different blocks containing 50%, 75%, or 100% valid trials. Four analyses were conducted: (i) an event-related analysis comparing invalid and valid trials, (ii) a blocked analysis comparing blocks with 50% valid and invalid trials to blocks with 100% valid trials, (iii) a blocked analysis detecting differences between block models when modeled as epochs or chains of events, and (iv) a blocked analysis that modeled blocks as chains of events to scale regressors equally to the event-related analysis. Irrespective of the type of analysis (blocked or event related), significant activation of the right intraparietal sulcus was observed. A larger cluster size was evident in the blocked analysis, which can be attributed to higher efficiency. In addition to this common right parietal activation, the event-related analysis revealed activations in right superior parietal cortex and left intraparietal sulcus. In contrast, the blocked analysis yielded additional activity in the right occipitoparietal junction. No influences of the block model (epoch versus chain of events) were found in regions activated in the blocked or event-related analysis, respectively. In summary, using a hybrid design and both event-related and blocked analysis techniques, we show both sustained and transient neural processes underlying reorienting of visuospatial attention.

Adult↗

PubMed2004

Different anaphoric expressions are investigated by event-related brain potentials.

Event-related potentials were recorded to substantiate the claim of a distinct psycholinguistic status of (a) pronouns vs. proper names and (b) ellipses vs. proper names. In two studies 41 students read sentences in which the number of intervening words between the anaphor and its antecedent was either small or large. Comparing the far with the near distance condition revealed anaphor resolution specific effects: Ellipses triggered a potential shift with a short latency (approximately 120-200 ms) and with a fronto-central scalp distribution while pronouns and proper names triggered one with a longer latency (approximately 360-440 ms) and a parietal to right-occipital distribution. The early effect resembled the left-anterior negativity which has been related to syntax processing, while the latter resembled an N400 which is assumed to reflect semantic integration processes. These findings support the idea that ellipses and pronouns/proper names are processed by distinct mechanisms being implemented in distinct cortical cell assemblies.

Adult↗

PubMed2004

Comparing arithmetic and semantic fact retrieval: effects of problem size and sentence constraint on event-related brain potentials.

Event-related potentials were recorded with 61 electrodes from 16 students who verified either the correctness of single-digit multiplication problems or the semantic congruency of sentences. Multiplication problems varied in size and sentence fragments in constraint. Both semantic and arithmetic incongruencies evoked a typical N400 with a clear parieto-central maximum. In addition, numerically larger problems (8x7), in comparison to smaller problems (3x2), evoked a negativity starting at about 360 ms whose maximum was located over the right temporal-parietal scalp. These results indicate that the arithmetic incongruency and the problem-size effect are functionally distinct. It is suggested that the arithmetic and the semantic incongruency effects are both functionally related to a context-dependent spread of activation in specialized associative networks, whereas the arithmetic problem-size effect is due to rechecking routines that go beyond basic fact retrieval.

Attention↗

PubMed2004

The redundant target effect is affected by modality switch costs.

When participants have to respond to stimuli of two modalities, faster reaction times are observed for simultaneous, bimodal events than for unimodal events (the redundant target effect [RTE]). This finding has been interpreted as reflecting processing gains for bimodal relative to unimodal stimuli, possibly due to multisensory interactions. In random stimulus sequences, reaction times are slower when the stimulus is preceded by a stimulus of a different modality (modality switch effect [MSE]). Simple reaction time redundant target experiments with auditory-visual, visual-tactile, and auditory-tactile stimulus combinations were run to determine whether the RTE may be partly explained by MSEs because bimodal stimuli do not require a modality switch. In all three modality pairings, significant MSEs and RTEs were observed. However, the RTE was still significant after reaction times were corrected for the MSE, supporting the hypothesis that coactivation occurs independently of modality switch costs.

Adult↗

PubMed2003

Memory for environmental sounds in sighted, congenitally blind and late blind adults: evidence for cross-modal compensation.

Several recent reports suggest compensatory performance changes in blind individuals. It has, however, been argued that the lack of visual input leads to impoverished semantic networks resulting in the use of data-driven rather than conceptual encoding strategies on memory tasks. To test this hypothesis, congenitally blind and sighted participants encoded environmental sounds either physically or semantically. In the recognition phase, both conceptually as well as physically distinct and physically distinct but conceptually highly related lures were intermixed with the environmental sounds encountered during study. Participants indicated whether or not they had heard a sound in the study phase. Congenitally blind adults showed elevated memory both after physical and semantic encoding. After physical encoding blind participants had lower false memory rates than sighted participants, whereas the false memory rates of sighted and blind participants did not differ after semantic encoding. In order to address the question if compensatory changes in memory skills are restricted to critical periods during early childhood, late blind adults were tested with the same paradigm. When matched for age, they showed similarly high memory scores as the congenitally blind. These results demonstrate compensatory performance changes in long-term memory functions due to the loss of a sensory system and provide evidence for high adaptive capabilities of the human cognitive system.

Acoustic Stimulation↗

PubMed2003

Differences in incidental and intentional learning of sensorimotor sequences as revealed by event-related brain potentials.

The present study investigated differences in sequential learning between subjects who were or were not informed of the presence of a repeating sequence (intentional or incidental group, respectively). Subjects had to learn a 16-letter-long repeating sequence that was irregularly disrupted by deviating stimuli. Reaction times indicated that both groups learned the sequential regularities. Intentional learners showed a larger learning effect. Event-related brain potentials (ERPs) recorded during performance of the task showed a reliably enhanced amplitude for the N2b- and P3b-components for deviant letters for intentional learners, but not for incidental learners. These results are discussed in the context of models proposing that different neural structures are involved in implicit and explicit serial learning.

Adult↗

PubMed2003

Differences between noun and verb processing in a minimal phrase context: a semantic priming study using event-related brain potentials.

The aim of the present study was to enforce the priming of either nouns or verbs in order to evoke word-category-specific N400 effects. In two experiments two primes which were either a verb-noun or a noun-noun pair were followed by a semantically related or unrelated target which was a noun or verb, respectively. This target always completed the word sequence to a minimal phrase comprising verb, subject, and object (VNN or NNV triplets). In experiment I subjects judged the semantic relatedness of the target to the two primes, in experiment II subjects first generated an appropriate target of the required word category and then judged the semantic relatedness between self-generated word and target. ERPs were recorded from 124 scalp electrodes. In both experiments verbs and nouns as such evoked reliably distinct ERP topographies between 300 and 800 ms. With verbs in relation to nouns the amplitudes were most often found to be more positive over central to frontal or parietal areas and more negative over occipital and temporo-parietal areas. In contrast, N400 effects proved as topographically invariant for noun and verb targets in both experiments. The results suggest that access to noun and verb representations involves topographically distinct cell assemblies while the N400 effect seems to reflect semantic evaluation and integration processes which are more abstract and independent from a particular word category.

Adult↗