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G Mulder

Publications and source records attributed to G Mulder.

At least 37 records · Page 2Linked to original sources
PubMed1993

Topography and source analysis of brain activity associated with selective spatial attention and memory search.

We investigated the topographical aspects of the ERP reflections of visual spatial attention and memory search. Spatial attention was found to enhance the amplitudes of the P1 and N1 deflections. The brain activity in the P1-N1 latency range could be modeled with a single moving equivalent dipole, or alternatively with two stationary dipoles in a spatio-temporal dipole model. The dipoles were located in mesial and lateral posterior brain regions. Similar dipole solutions were obtained for ERPs to attended and unattended stimuli. Increasing the memory search requirements of the task resulted in an increase of late negativity, which was topographically distinguishable from the P3 component.

Attention↗
PubMed1993

Fibrin cuff lysis in chronic venous ulcers treated with a hydrocolloid dressing.

BACKGROUND: Pericapillary fibrin cuffs (PFC) are a recognized part of the pathology of venous stasis ulcers. A hydrocolloid dressing capable of lysing wound surface fibrin was tested in venous ulcers for its capacity to lyse pericapillary fibrin below the wound surface. METHODS: Tissue biopsies from the rims of 19 venous ulcers were evaluated for thickness of shallow and deep dermal PFCs before and after treatment with DuoDERM covered by Unna's boot and a compression bandage (DD+UB; n = 9) versus the same treatment without the hydrocolloid dressing (UB; n = 10). Frozen sections of all biopsies were stained with an immunofluorescent antibody to fibrin for rating of PFC thickness. Separate sections were stained with hematoxylin and eosin to assess capillary frequency, histopathology, and inflammation. All ratings and pathology assessments were performed blinded to treatment conditions. RESULTS: Both deep and shallow PFCs were reduced in 89% of ulcers treated with DD+UB versus 40% of ulcers treated with UB (alpha < 0.04). No other significant differences in inflammation, histopathology, or capillary frequency were observed. CONCLUSIONS: Treatment with DD+UB reduced PCFs in twice the number of ulcers than UB alone in 1 week. This is the first scientific documentation that a topical wound dressing could reduce the pathophysiology associated with venous ulcers, beyond the known beneficial effect of graduated compression. Not all hydrocolloid dressing are fibrinolytic, so this effect may not generalize to other dressings.

Bandages↗
PubMed1992

A psychophysiological study of the use of partial information in stimulus-response translation.

Ss performed a hybrid go/no-go reaction task in which colored letters were assigned in various ways to 4 finger responses, 2 on each hand. In addition to reaction time, psychophysiological measures were used to assess the duration of stimulus identification and the onset of central and peripheral motor activity. The results suggest that response selection can begin on the basis of 1 stimulus dimension (e.g., color), while the other dimension (e.g., letter form) has not yet been identified. Other results are discussed with regard to "selection for action" (Allport, 1987) and the importance of stimulus-response translation strategies in the use of partial information.

Adult↗
PubMed1992

An electrophysiological study of semantic processing in young and middle-aged academics.

This study explored age differences in the N400 component, described by Kutas and Hillyard as an index of semantic expectancy. A group of young students and a group of middle-aged academics read a number of congruent and incongruent sentences followed by a recognition task. Age differences were found in both accuracy and speed in the recognition task. The N400 elicited in the reading task was both delayed in latency and reduced in amplitude in the older group. These aging effects could not be attributed to early stimulus input processes because the N1 did not differ between the age groups. A re-averaging of the event-related potentials during reading as a function of subsequent recognition showed a small memory-related positivity for the younger group and a large memory-related positivity for the older group, suggesting a difference in the encoding strategies of the two groups. To check the generalizability of the results of this particular age group, a further task (a memory scanning task) was carried out. The results, a delayed P3b and an increased reaction time, matched those found in the literature.

Adult↗
PubMed1991

Psychophysiological evidence for continuous information transmission between visual search and response processes.

This study was designed to test whether information transmission between the perceptual and motor levels occurs continuously or in discrete steps. Ss performed visual search across nontargets that shared visual features with one of two possible targets, each assigned to a different response. In addition to reaction time, psychophysiological measures were used to assess the duration of target search and the onset of central and peripheral motor activity. Nontargets sharing features with a target selectively activated the response associated with that target, even when it was not present in the display. This suggests that information transmission to the motor level can consist of fine-grained visual information and that visual search and response selection occur in parallel.

Adult↗
PubMed1991

On the usefulness of finger blood-pressure measurements for studies on mental workload.

Two experiments were conducted to explore the usefulness of the Penaz method for non-invasive, continuous finger blood pressure measurements during mental stress testing. In the first study, blood pressure was measured with the Penaz method, in the second it was measured intra-arterially. Two different subject groups were used. In both experiments the same mental task, a memory search and counting task, was used. Experimental effects, consisting of rest-task differences in heart rate and blood pressure, its (spectral) variability and the coherence between fluctuations in the two signals (e.g. baroreflex sensitivity) are compared for the two measuring methods. Experimental effects on mean pressure values, spectral variability measures and baroreflex sensitivity are similar for the two types of measurement. Effects on mean pressure are smaller in the finger pressure indices. It is concluded that the Penaz instrument can provide us with a useful method for studying cardiovascular reactivity in mental stress research.

Adolescent↗
PubMed1990

Selective response activation can begin before stimulus recognition is complete: a psychophysiological and error analysis of continuous flow.

In discussions of process models of human information processing, the continuous flow conception (Eriksen and Schultz 1979) plays a prominent role. A central prediction of this conception is that any information in a display associated with a response activates that response as soon as it becomes available in the perceptual system. If it concerns the correct response channel, then response facilitation occurs. If it concerns the incorrect response channel, then response competition occurs. To assess these mechanisms more directly, we used psychophysiological measures as well as reaction time (RT). We used the latency of the P3 component of the event related brain potential (ERP) as an index of stimulus evaluation duration, the onset of lateralized motor activity derived from the ERP as an index of selective central motor activation, and the onset of electromyographic activity as an index of the start of peripheral motor activation. Subjects were required to respond to target letters that were either flanked by letters that signalled the opposite response (incompatible arrays), by the target itself (compatible arrays), by letters not associated with a response (neutral arrays), or by no other letters (targets alone). Our results replicated the basic findings obtained in this paradigm. RTs to targets alone did not differ from RTs to compatible arrays. The latter were faster than RTs to neutral arrays, which were faster than RTs to incompatible arrays. P3 latencies were longer on incompatible than on neutral trials, and longer on compatible than on target alone trials. Incorrect central response activation on incompatible trials and correct central response activation on compatible trials, both began earlier than on target alone trials. Peripheral responding on both trial types, however, began later than on target alone trials. More incompatible but less compatible trials than neutral ones exhibited incorrect peripheral response activation. Peripheral response execution was faster and more accurate on compatible than on target alone trials, while it was slower and less accurate on incompatible than on neutral trials. These results indicate, that the flankers activated their associated response channel while display evaluation was still going on, and that response facilitation and competition occurred. After applying criteria proposed by Miller (1988), it was concluded that the set of stimulus recognition processes and the set of response activation processes cannot be regarded as independent stages of processing.

Adult↗
PubMed1990

The effectiveness of Dry Bed Training for nocturnal enuresis in adults.

Nine enuretic adults were successfully treated by the Dry Bed Training in a fairly short time (means = 15 weeks) including the retraining period for 3 Ss who relapsed after the therapy. There were no differences between primary and secondary (nocturnal) enuretics. The few relapses were neutralized by a short retraining. The study shows that this minimal intervention treatment is effective and efficient.

Adult↗
PubMed1989

An electrophysiological investigation of the spatial distribution of attention to colored stimuli in focused and divided attention conditions.

In the present experiment ERPs were recorded to colored stimulus bars (red or blue) which were randomly presented at one out of eight different spatial locations on a visual display. The locations were situated on a hemi-circle around the fixation point, with four locations lying in each visual half-field. The subjects were instructed to attend to one stimulus location (the most peripheral left or right location: the relevant location) in a focused attention condition and to all four locations within the same visual half-field in a divided attention condition, and were instructed to respond to stimulus bars in one color presented at the relevant location(s). In the focused attention condition, spatial attention resulted in early positivity in the P1 latency range (ca. 100-175 ms), followed by a prolonged negativity in the N1, P2, and N2 latency range (ca. 175-350 ms). These effects generalized to locations in the same visual half-field as the relevant location. The effect of attending and responding to the target color consisted of a number of different effects. An early anterior positivity, occipital negativity was observed for the relevant location and for locations in the same visual half-field as the relevant location, but not for the locations in the opposite visual field. A later central negativity (N2b) appeared to be confined to the relevant location and one location adjacent to it. Finally, a late parietal positivity (P3b) was exclusively evoked by target stimuli at the relevant location. In the divided attention condition, the ERPs evoked by stimuli presented at each of the four locations within the relevant visual half-field showed increased early positivity (enhancing P1 amplitude) as compared to the ERPs to stimuli in the opposite (irrelevant) visual half-field. The early color selection effect was also found to all stimuli within the relevant half-field, but the N2b component was evoked both by stimuli within the relevant half-field and by stimuli at the location in the irrelevant half-field closest to the midline. The P3b was present to target stimuli at the three most lateral positions within the relevant half-field but it was absent to the relevant location closest to the midline. The data suggested that the attentional spotlight encompassed at least approximately 2 degrees in the focused attention condition, and an efficient selection by visual half-field in the divided attention situation.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1989

Event-related potentials during memory search and selective attention to letter size and conjunctions of letter size and color.

The analysis of event-related potentials was used in two experiments to investigate the structure of information processing in a task in which subjects selectively attended to letter size (Experiment 1) or a conjunction of letter size and color (Experiment 2) and searched for target letters within the attended stimulus category. The event-related potentials showed that selective attention to letter size resulted in the enhancement of a central N2b component (onset about 200 ms), which was assumed to reflect feature nonspecific orienting of attention. When attention was directed to conjunctions of letter size and color an earlier effect was found (onset about 150 ms) consisting of positivity at the anterior electrodes and negativity at OZ. This earlier effect was assumed to reflect feature-specific selective processing. Although the early effect showed a hierarchical pattern of results, in which the effect of attending to size was contingent on the relevance of the color attribute, the N2b showed a more independent pattern of results, in which the relevance of either the color or the size attribute resulted in an enhancement of this component, independent of the relevance of the other attribute. An increase in the duration of the memory search process resulted in a prolonged negativity with an onset of about 200 ms which was maximal at CZ. In both experiments the initial phase of this negativity was also found in the event-related potentials to the unattended stimulus categories, suggesting that the search process was initiated nonselectively and terminated after the selection cues were identified. Detection of attended target letters resulted in a parietal P3b component. In both experiments there was an earlier effect discriminating targets and nontargets in the range 200-300 ms.

Adult↗
PubMed1989

Brain potentials during selective attention, memory search, and mental rotation.

Event-related potentials were measured in a task that combined the classic selective attention paradigm with memory search and mental rotation paradigms. Subjects were required to attend to stimulus letters in one color and to ignore stimuli in a different color. Within the attended category subjects searched for target letters from a prememorized set (the memory set) and indicated whether they were presented normally or in mirror-image. Letters in all stimulus categories were presented randomly in either their upright position or rotated over 60 degrees, 120 degrees, or 180 degrees. The event-related potentials showed that the earliest effect of attending to color was a positivity at the anterior electrodes and a negativity at Oz (onset about 150 ms), followed by the enhancement of a central N2 component (N2b, onset about 220 ms). The early effect is thought to reflect selective processing of elementary stimulus features, the later N2b the covert orienting of attention. A later, prolonged central negativity elicited by attended stimuli covaried with the duration of the memory search process. Target detection resulted in a parietal P3b component, and also in an earlier negativity (in the range approximately 200-300 ms) to both attended and unattended targets, suggesting an early preattentive target classification. There were two effects of the rotation of stimuli. First there was an early occipital effect (about 200-300 ms), irrespective of attention and stimulus categories. It was argued that this effect reflected the preattentive identification of the orientation of the stimulus letters. A later (onset about 350-400 ms) parietal effect consisted of an increase in negativity as a function of the angle over which letters were rotated. This prolonged negativity had a later onset latency than the search-related negativity, and was restricted to the event-related potentials to target letters in the attended input channel. It was suggested that this component is the manifestation of a mental rotation process. It was argued that rotation-related negativity and memory search-related activity reflect operations in distinct working memory subsystems.

Adult↗
PubMed1989

Attention to color: an analysis of selection, controlled search, and motor activation, using event-related potentials.

In this study the organization of information processing in a selective search task was examined by analyzing event-related potentials. This task consisted of searching for target letters in a relevant (attended) color. The ERPs revealed two different effects of attention: an early occipital negativity (+/- 150 ms) reflecting feature-specific attention, and a later, central N2b component (+/- 240 ms) reflecting covert orienting of attention. A later, prolonged negativity (search-related negativity) (+/- 300 ms), maximal at Cz, was related to controlled search to letters in the attended color. Detection of relevant targets resulted in a parietal P3b component. Depending on stimulus presentation conditions an earlier response to both attended and unattended targets was found: an N2 component (+/- 250 ms). In these same conditions, C'3-C'4 asymmetries (Corrected Motor Asymmetries--CMA) suggested motor activation at +/- 300 ms, in the same time range as search-related negativity. It was argued that N2 and CMA suggest the existence of a preattentive target detection system, operating in parallel with a slower serial attentive system, as reflected by N2b and search negativity.

Adult↗
PubMed1988

Use of partial stimulus information in response processing.

We examined the reaction time benefit that is obtained when salient features of the stimulus set and response set correspond. Components of the event-related brain potentials were used to measure the timing of stimulus-related and response-related processes in order to determine the locus of this effect. Of particular importance was the development of a new index of selective response preparation, the corrected motor asymmetry (CMA). We found no evidence for the use of preliminary, partial stimulus information in response preparation. These results suggest that the benefit is located primarily in response selection processes and probably reflects a more efficient algorithm for stimulus-response translation. Also, we found trial-to-trial variability in the duration of response selection to be the major determinant of variability in reaction time, whereas the durations of subsequent response-related processes were relatively invariant. Implications of these results for discrete and continuous models of choice reaction performance are discussed.

Adult↗
PubMed1987

Visual search and spatial attention: ERPs in focussed and divided attention conditions.

ERPs and performance were measured in divided and focussed attention visual search tasks. In focussed attention tasks, to-be-attended and to-be-ignored letters were presented simultaneously. We varied display load, mapping conditions and display size. RT, P3b-latency and negativity in the ERP associated with controlled search all increased with display load. Each of these measures showed selectivity of controlled search, in that they decreased with focussing of attention. An occipital N230, on the other hand, was not sensitive to focussing of attention, but was primarily affected by display load. ERPs to both attended and unattended targets in focussed attention conditions showed and N2 compared to nontargets, suggesting that both automatic and controlled letter classifications are possible. These effects were not affected by display size. Consistent mapping resulted in shorter RT and P3b-latency in divided attention conditions, compared to varied mapping conditions, but had no effect in focussed attention conditions.

Adolescent↗
PubMed1987

Assessment of baroreceptor reflex sensitivity by means of spectral analysis.

A method of determining baroreceptor reflex sensitivity is proposed that is based on spectral analysis of systolic pressure values and RR interval times, namely, the modulus (or gain) in the mid frequency band (0.07-0.14 Hz) between these two signals. Results using this method were highly correlated (0.94; n = 8) with results of the phenylephrine method. In addition, compared with the values for the preceding rest period, the modulus decreased during mental challenge, as might be expected from the literature.

Adult↗