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F Rösler

Publications and source records attributed to F Rösler.

At least 19 recordsLinked to original sources
PubMed1996

Event-related potentials during auditory and somatosensory discrimination in sighted and blind human subjects.

The objective of the present study was to test if and to what extent phasic and tonic event-related potentials of the human EEG may reflect phenomena of cortical plasticity. In particular, it was tested if the occipital cortex of blind subjects participates in the processing of non-visual stimuli. To this end, 12 blind and 12 blindfolded sighted subjects were tested in an auditory and a somatosensory discrimination task with 2 levels of discrimination difficulty. Slow and fast event-related potentials were recorded from 18 scalp electrodes. In addition to the negative slow waves found in sighted subjects over frontal and central sites during auditory and somatosensory discrimination, a pronounced negative wave was revealed in the blind also over occipital brain areas. These negative shifts were time-locked to the train of stimuli which had to be monitored with sustained attention, i.e. they rised and resolved with the beginning and the end of a 20-s discrimination time epoch. The P300 complex, on the other hand, which is a slow positive deflection over the posterior part of the scalp and which follows rare and task-relevant events 200-800 ms after stimulus onset was significantly smaller at occipital electrodes in the blind than in the sighted subjects. Combined with neurophysiological and neuronanatomical evidence originating from studies with visually deprived animals, these data suggest that the occipital cortex of blind human subjects is coactivated whenever the system is engaged in a task which requires sustained attention and is less effectively inhibited at the end of a perceptual time epoch. In total, the data cast doubt on the hypothesis that the occipital cortex of blind subjects participates in modality-specific non-visual information processing.

Adult↗
PubMed1995

Stimulus-induced gamma oscillations: harmonics of alpha activity?

Event-related changes of spectral power of the EEG were studied for each integer frequency between 5 and 100 Hz in three subjects during memory storage and retrieval. Spectra were calculated for successive, overlapping time epochs in seven channels. In one subject a stimulus-locked increase of power was observed at 12 Hz, while in the other two alpha power decreased at the individual peak frequencies of 9 and 11 Hz, respectively. In all subjects corresponding changes of power appeared at frequencies which were integer multiples of the individual dominant alpha frequencies. An analysis of the cross covariance of the alpha, beta and gamma activity revealed high coefficients for harmonic frequencies only while all other covariances were negligibly small. It is argued that event-related gamma activity may be an epiphenomenon of event-related changes within the alpha band.

Adult↗
PubMed1995

Exploring memory functions by means of brain electrical topography: a review.

A series of experiments is reviewed which explored whether the functional brain state of long-term memory retrieval is correlated with specific changes in slow, DC-like event-related brain potentials. The main results are: (1) Retrieving associations from long-term memory is accompanied by a slow negative shift of 5-10 microV which prevails about as long as the retrieval process lasts, i.e., in our experiments, for a period of several seconds: (2) When different types of representations have to be reactivated in memory the slow negative wave shows a clearly distinct topography. The maximum was found in a verbal condition over the left frontal, in a spatial condition over the parietal, and in a color condition over the right occipital to temporal cortex. All these conditions were completely equivalent with respect to the established associative structure, the learning procedure, and the performance criterion. (3) The amplitude of the topographic maximum increases with the number of representations which have to be reactivated. This effect is not due to a non-specific increase of effort but specifically related to the number of activated episodic memory contents which had been experimentally established. In contrast, the reactivation of a priori given semantic association did not become manifest in a specific slow wave effect. These findings are compatible with the idea that memory retrieval implies a reactivation of those cortical cell assemblies in the cortex in which the constituting features of a mnestic entity had originally been processed during perception and learning. The results are also discussed with respect to the possible advantages of EEG and MEG recordings for a cognitive psychophysiology in comparison to other brain imaging techniques as PET or fMRI.

Brain↗
PubMed1995

Patterns of cerebral activation while mental images are rotated and changed in size.

Event-related brain potentials were recorded while subjects performed either a rotation or a size scaling transformation of a mental image. Images had to be rotated 0 degrees, 60 degrees, or 120 degrees or their size had to be enlarged by factors of 1:1, 1:3, or 1:5. Both tasks were accompanied by pronounced negative slow potentials, which extended over several seconds. The relative maximum of these shifts emerged at central to occipital leads. Over the occipital cortex, the negative potential had a similar amplitude level in all conditions and both tasks. However, at parietal and central areas, the negative slow wave changed in relation to the difficulty of the task. The amplitude increased with increasing rotation demands and if the scaling operation required an exact computation of the coordinates of the image. None of these effects could be attributed to an inverse change of P300.

Adult↗
PubMed1994

Dynamics of activation in long-term memory: the retrieval of verbal, pictorial, spatial, and color information.

Paivio's (1986) dual code theory was tested in 5 experiments with a new paradigm for the FAN effect that enforced genuine memory recall. Subjects had to learn associations between concepts and mediators. The FAN of the concepts in relation to the mediators was varied systematically. Response times (RT) were measured while subjects had to decide whether 2 concepts were linked to each other or not by a common mediator. In Experiment 1 the concepts and mediators were words, whereas in the other experiments the concepts were line drawings. Colors served as mediators in Experiment 2 and spatial locations served as mediators in Experiments 3, 4, and 5. All of the experiments were equivalent with respect to the FAN, the learning procedure, and the retrieval test. In all of the experiments, RT proved to be a linear function of the FAN. These results suggested that the same dynamics hold for all types of information stored in long-term memory.

Adolescent↗
PubMed1993

A psychophysiological analysis of response-channel activation and outcome states in Eriksen's noise-compatibility task.

Eleven subjects were tested with a modified version of Eriksen's noise-compatibility task. Four noise conditions were realized--neutral, compatible, fully incompatible, and partially incompatible context. Target and flanking stimuli had an intrinsic association to either the left- or the right-hand side. As a response subjects pulled, with either their left or their right hand, an ordinary bicycle handbrake from a preload position towards a stop. The EMG from the forearm muscles and the movement trajectory were recorded continuously. Trials were categorized according to the outcome states, i.e., whether a full movement or only a rudimentary EMG activation had occurred in the correct and in the incorrect response channels, respectively, and whether the correct-channel activation was leading or lagging. Incompatible noise delayed information transfer and increased the likelihood of errors, while compatible noise had an opposite effect, i.e., it facilitated transfer and reduced the likelihood of errors. The effect of noise on transfer times was the same for all outcome states. Moreover, in all cases, noise had an effect on transfer times only up to the point of EMG onset, while it left movement-execution times unaffected. These findings are seen as contradictory to a strong continuous flow conception according to which any response-related change in the input channel is continuously and immediately transferred to the response-execution device. At least the final stage of movement control seems to be autonomous and not subject to input control, except for the case that a movement already initiated has to be aborted completely.

Adult↗
PubMed1993

A correction method for DC drift artifacts.

In order to cope with the problem of drift artifacts in ERP research a new off-line correction method is described. It estimates the DC drift from all prestimulus baselines of an experiment. For this end, an amplifier reset is performed at regular intervals and the DC off-set preceding any reset is stored. A regression is calculated between the prestimulus baseline amplitudes of consecutive trials and the time that has passed by. The amplitude trend which can be explained by either a linear or non-linear regression model is then subtracted from all data points. The power of the method is illustrated by two examples. The first shows that detrending increases the signal-to-noise ratio in ANOVA designs. The second shows that amplitude differences of event-related slow potentials, which appeared between the first and the second half of an experiment, could be explained by a non-linear drift component.

Analysis of Variance↗
PubMed1993

Topographic differences of slow event-related brain potentials in blind and sighted adult human subjects during haptic mental rotation.

Twelve blindfolded sighted, nine congenitally blind, and seven adventitiously blind subjects were tested in a haptic mental rotation task while slow event-related brain potentials in the EEG were recorded from 17 scalp locations. The overall topography of the slow wave pattern which prevailed during the task differed for sighted and for blind, but not for congenitally and adventitiously blind subjects. While the tactile stimuli were encoded, the blind showed a pronounced occipital and the sighted a pronounced frontal activation. The task-specific amplitude increment of a negative slow wave which can be understood as a manifestation of the process of mental rotation proper, showed a different topography for sighted and for blind subjects too. It had its maximum over central to parietal cortical areas in both groups, but it extended more towards occipital regions in the blind. In both groups, the effects were very similar to those observed in former studies with visual versions of the mental rotation task, i.e. the slow wave amplitude over central to parietal areas increased monotonously with an increasing angular disparity of the two stimuli to be compared. These results are discussed with respect to the question of whether visual deprivation in the blind can cause a reorganization of cortical representational maps.

Adult↗
PubMed1993

Imagery-perception interaction depends on the shape of the image: a reply to Farah (1989).

Farah (1989) reported that point threshold stimuli are detected better if they appear at spatial locations in the visual field that are covered by an image. By replicating her experiment with 3 instead of the original 2 images, we found that the effect depends on the shape of the mentally projected image. A second experiment with 9 different shapes revealed that the effect is modulated by the compactness and the size of the image--it is enhanced with increasing compactness and attenuated with increasing size. These findings do not unequivocally support the idea that imagery and perception interact because both processes share the same representational medium. Rather, they suggest that imagery can cause a figure-ground segregation in the visual field and that the shape of the figure may determine the amount of attention that is allocated to different sections in the visual field.

Eidetic Imagery↗
PubMed1993

Monitoring retrieval from long-term memory by slow event-related brain potentials.

Slow event-related brain potentials of nine subjects were recorded in an experimentally controlled long-term memory retrieval task (the Fan paradigm) from electrode sites F3, Fz, F4, Cz, P3, Pz, and P4. In all retrieval conditions, a very pronounced DC-like negative potential appeared over the left frontal cortex. This negativity was switched on with the presentation of the probe stimuli and prevailed in some conditions throughout the total recording epoch of 14 s. Particular retrieval conditions became manifest in distinct slow wave effects. The amplitude of a bilaterally distributed frontal negative slow wave increased when a more diversified associative structure had to be searched. The amplitude of another negative slow wave, which peaked bilaterally over parietal areas, was affected by the type of concepts that had to be retrieved. The amplitude was larger with general concepts (category labels) and smaller with specific concepts (category exemplars). These results suggest that distinct strategies are invoked when subjects are required to draw conclusions about different contents stored permanently in an associative network.

Adult↗
PubMed1993

[Research strategies in cognitive psychophysiology].

Two research strategies of cognitive psychophysiology are explained and illustrated by means of examples. In psychophysiological chronometry latencies of distinct events are measured from various biosignals (electroencephalogram, electromyogram, overt responses). These data provide insight into when a hypothetical processing module is activated, how long it is active and how long it takes to transfer information from one module to another. Among others, this approach allows to investigate whether particular processing steps are running in a sequential or a parallel mode. In a second approach event-related brain potentials which accompany well defined steps of information processing are analysed. Their topography provides information about which cortical areas are involved during particular steps of information processing and their amplitude indicates the load which is imposed on these areas. Both research strategies make it possible to study features of the human information processing system before an overt response has been committed. Implications which follow from these methodological approaches for fields of basic and applied research are mentioned (e.g. for cognitive, pharmaco- and neuropsychology).

Arousal↗
PubMed1993

[Haptic mental rotation in patients with congenital blindness, acquired blindness and normal vision persons].

Nineteen congenitally blind subjects (Ss), eleven Ss who went blind later in their life, and 42 control Ss with normal vision were tested in a tactile version of a "mental rotation" task. A specially constructed tactile display was used which enabled a rotation of the alphanumeric symbols in multiples of 60 degrees without any form distortion. Ss had to compare two successively presented symbols regarding whether the second was just a rotated version or also a mirror image of the first. Decision latencies and errors were recorded. Neither of dependent variables reveal any differences between the three groups of subjects. Moreover, the well known linear increase of decision latency as a function of angular disparity could also be observed with the tactile stimuli in all three groups. Both results are consistent with the assumption that mental rotation effects are neither linked to the visual modality nor to a manipulation of visual-analog representations. If the task is solved by so called analog processes then these seem to operate with non-visual spatial representations.

Adult↗
PubMed1991

Toward a functional categorization of slow waves: taking into account past and future events.

Ruchkin, Johnson, Mahaffey, and Sutton (1988) presented evidence for a frontal positive/posterior negative late slow wave (SW) which they found to be functionally related to conceptual load, i.e., the difficulty of mental calculation problems increased both the positive and negative parts of it. In the present study we replicated the paradigm of Ruchkin et al. with some modifications, and we also found that this late SW pattern is actually due to a superimposition of two slow potentials. Our results suggest that one potential (positive at frontopolar scalp) is related to the mental operation of division. However, the other potential (negative over posterior scalp) is not related to the computational task itself but to the expectation of stimuli that follow the task. In addition, we found that memorizing a digit seems to be associated with a positive slow wave over posterior scalp. Altogether, our data suggest that load imposed on working memory is associated with positive slow waves which show a task specific topography--mental division is associated with a pSW at FPZ, remembering with a pSW at PZ/OZ. On the other hand, the state of stimulus and task anticipation is associated with negative slow waves. The latter reach their amplitude maximum over posterior scalp, if visually presented information is anticipated. Our study demonstrates how functionally distinct slow waves can be disentangled by a systematic manipulation of events which either precede or follow the slow wave activity. Moreover, it shows that recording epochs must be of considerable length, if the functional significance of slow waves is the objective of research.

Adult↗
PubMed1991

[Psychophysiologic chronometry: detection of facilitating and inhibiting processes in information processing using electroencephalographic and electromyographic data].

The objective of the present research was to tally the potential usefulness of psychophysiological measures in the systematic analysis of human information processing. Different context conditions were established in two cued choice-reaction time experiments. The context could either facilitate or inhibit the processing of an imperative stimulus. Event-related brain potentials (EEG-ERP) and event-related electromyograms (EMG-ERP) were recorded and from these biosignals latencies and duration times for different aspects of stimulus evaluation and movement execution were derived. The EEG-ERP provided measures for the time of primary stimulus categorization (N2), the time necessary to test actual stimulus information against stimulus expectancies (P3b), and the time necessary to check the decision about the stimulus-response mapping (pSW). From the EMG-ERP, processing times were derived which are related to the initiation of a motor program and to distinct sections of the movement trajectory. Results show that these latency measures react differently to different context manipulations. EEG-ERP measures, for example, reflected differences during stimulus evaluation which were not detectable in response- or EMG-derived movement times. The parallel analysis of EEG-ERPs and EMG-ERPs allowed delineation of processing modules which are responsible for particular context-dependent facilitation and inhibition effects. Moreover, the data revealed substantial overlap of evaluation times and movement times. This finding seems to be more compatible with a parallel processing model than with a strictly sequential model.

Adult↗
PubMed1986

The double-priming paradigm: a tool for analyzing the functional significance of endogenous event-related brain potentials.

A new paradigm to study the functional significance of 'P300' is presented. Its advantages are: The precise definition and manipulation of cognitive operations which are triggered by the very same events as used for ERP extraction; and a systematic control over the probability of events known to affect endogenous event-related potential components (probabilities of single events, event categories, and event sequences). By employing the paradigm in two experiments with visual stimuli, three subcomponents of 'P300' were identified: P3a; P3b; and positive Slow Wave (pSW). Experimental manipulations revealed that P3b is related to the information processing resources required to alter a perceptual set and pSW to the resources required when abstract information permanently stored in memory must be retrieved. The data further revealed that the same-different disparity in response latency for matching letters has at least two ERP correlates: A difference in P3b latency; and a difference in the amplitude of a negative recess between P3a and P3b.

Adult↗
PubMed1986

Flupentixolhydrochloride in low dosages: effects on perceptual and psychomotor performance in emotionally stable and emotionally labile healthy subjects.

Effects of flupentixol on performance were evaluated in a double-blind study with 107 healthy male subjects. Experimental factors were dosage (0, 1, and 2 mg Fluanxol 0.5/day), the trait variable 'neuroticism' (high vs. low score on a questionnaire scale), and time of measurement (before and after 4 days of treatment). Drug effects were measured by means of seven paper-and-pencil tests and eight apparatus tests covering the following cognitive functions: endurance in attention, spacial orientation, flexibility and speed of closure, perceptual speed, response speed, psychomotor coordination, knowledge of traffic rules, and basic motoric tempo. Univariate and multivariate ANOVAs disclosed that flupentixol has detrimental effects on perceptual and psychomotor functions, in particular when administered in a dosage of 2 mg/day. These treatment effects did not interact with the trait variable neuroticism. Nevertheless, there were substantial differences between emotionally stable and emotionally labile subjects in both absolute performance level and change of performance over time.

Adult↗