Improving rowing performance by adjusting oar blade size and angle

The principal aim of the work presented here is to investigate and demonstrate that a forward tilted rowing blade would result in a more efficient and effective motion of the blade through the water that would result in a higher boat speed when an equal input power is provided. A 1:5 scaled rowing boat is used to determine the performance of rowing blades with different sizes and blade angles. This is used to validate the results of a previous study where the optimal blade angle of 15o with respect to the oar shaft was determined ( 1). The input power and speed of the rowing boat can be compared between original and modified oar blades. Measurements in a towing tank demonstrate that a modified rowing blade result in faster rowing by 0.4% at the same input power. Maintaining the same stroke rate, the improvement of the blade efficiency is compensated by using a 4–6% increased blade area to yield the same input power.

The influence of contrast agent injection on physiological flow in the circle of Willis

X-ray videodensitometry allows in vivo flow measurements from gradients in contrast agent concentration. However, the injection of contrast agent alters the flow to be measured. Here, the temporal, spatial, and inter-patient variability of the response to injection are examined. To this purpose, an injection is prescribed in the internal carotid in a 1D wave propagation model of the arterial circulation. Although the resulting effect of injection is constant over a cardiac cycle, the response does vary with the location within the cerebral circulation and the geometry of the circle of Willis. At the injection site, the injection partly suppresses the incoming blood flow, such that the distal flow is increased by approximately 10%. This corresponds to approximately 20% of the injection rate added to the blood flow during injection, depending on the vascular geometry. In the communicating arteries, the flow direction is reversed during injection. Since the measured flow is not equal to the physiological blood flow, the effect of injection should be taken into account when deriving the flow from travelling contrast agent.

Decision making performance in obsessive compulsive disorder

BACKGROUND

Neuro-imaging studies in OCD report the orbitofrontal cortex to be functionally abnormal. As these areas are presumed to be involved in decision making, studying this behavior in OCD may provide further insight into the cognitive deficits accompanying the disorder.

METHODS

Performance of 27 drug-free OCD patients and 26 healthy volunteers was compared on the decision making task of Bechara et al. [Cognition, 50 (1994) 7-15].

RESULTS

OCD patients and volunteers displayed comparable decision-making behavior. Within OCD patients, risk taking was independently related to both anxiety and OCD severity.

LIMITATIONS

Results must be regarded as preliminary, due to the limited number of OCD patients included and the lack of a clinical control group.

CONCLUSIONS

Although VMpfc function is not generally impaired, it seems to be involved in OCD; possibly in another way than could be measured with this task.

CLINICAL RELEVANCE

Clarification of cognitive distortions underlying OCD may guide development of new strategies for cognitive-behavioral therapy.

Selective attention to a facial feature with and without facial context: an ERP-study

The present experiment addressed the question whether selectively attending to a facial feature (mouth shape) would benefit from the presence of a correct facial context. Subjects attended selectively to one of two possible mouth shapes belonging to photographs of a face with a happy or sad expression, respectively. These mouths were presented randomly either in isolation, embedded in the original photos, or in an exchanged facial context. The ERP effect of attending mouth shape was a lateral posterior negativity, anterior positivity with an onset latency of 160-200 ms; this effect was completely unaffected by the type of facial context. When the mouth shape and the facial context conflicted, this resulted in a medial parieto-occipital positivity with an onset latency of 180 ms, independent of the relevance of the mouth shape. Finally, there was a late (onset at approx. 400 ms) expression (happy vs. sad) effect, which was strongly lateralized to the right posterior hemisphere and was most prominent for attended stimuli in the correct facial context. For the isolated mouth stimuli, a similarly distributed expression effect was observed at an earlier latency range (180-240 ms). These data suggest the existence of separate, independent and neuroanatomically segregated processors engaged in the selective processing of facial features and the detection of contextual congruence and emotional expression of face stimuli. The data do not support that early selective attention processes benefit from top-down constraints provided by the correct facial context.

Working memory processes show different degrees of lateralization: evidence from event-related potentials

This study aimed to identify different processes in working memory, using event-related potentials (ERPs) and response times. Abstract polygons were presented for memorization and subsequent recall in a delayed matching-to-sample paradigm. Two polygons were presented bilaterally for memorization and a cue indicated whether one (and if so, which one of the two) or both polygons had to be memorized. A subsequent test figure was presented unilaterally to the left or right visual field and had to be compared with the memorized figure(s). ERP results suggested that memorization takes place in a visual buffer in contralateral posterior brain areas, whereas identification of the test stimulus as a target appears to be mainly a left hemispheric process. Increased response times were found for nontarget test stimuli as compared to targets, and for target test stimuli that were presented contralaterally with respect to the location of the memorized stimulus. In addition, response times were slower when two figures were memorized than when only one was memorized.

Working memory constraints on syntactic processing: an electrophysiological investigation

Event-related potentials (ERPs) and reaction times (RTs) were used to study how the processing of sentences with morphosyntactic violations is constrained by working memory (WM) capacity. The available WM capacity was varied by three orthogonal manipulations: (1) syntactic complexity; (2) additional WM load; and (3) verbal WM span. The processing of the morphosyntactic violations was reflected in longer RTs in ungrammatical compared with grammatical sentences, and in an anterior negativity and a centroparietal positivity in the ERPs. While the behavioral grammaticality effect was not influenced by the WM manipulations, the ERP effects were. The amplitude of the anterior negativity was modulated by the combination of complexity and load, and by WM span. The onset of the centroparietal positivity was delayed in the high-load condition, and for the low-span group. ERPs over the course of the sentences showed a frontal negative slow wave under high WM load, largest for the low-span group. The finding that online syntactic processing is related to WM span and to additional WM load does not support the theory that there is a WM capacity specific for syntactic processing.

Visual semantic features are activated during the processing of concrete words: event-related potential evidence for perceptual semantic priming

There has been conflicting evidence to date regarding the existence of non-strategic semantic priming based on semantic similarity, and in particular on visual-perceptual semantic features (e.g., button-coin: words refer to objects with the same global shape). Both event-related potential (ERP) and reaction time (RT) measures were employed to investigate visual-perceptual semantic priming in a word-pair lexical decision task designed to minimise the contribution of conscious strategic processing. While no RT priming effect was observed, a robust priming effect was obtained on the N400 component of the ERP. This result shows that semantic priming, as indexed by the N400 component, can be supported by nonassociative visual-perceptual semantic relations. The data are consistent with perceptual form information being accessed during the processing of concrete words, and provide support for models of semantic representation which incorporate semantic features and form information.

Event-related brain potential and heart rate manifestations of visual selective attention

Twenty-eight volunteers were instructed to attend stimuli presented at one side of the computer screen and to ignore stimuli presented at the other side. Both attended and unattended stimulus series consisted of targets (25%) and nontargets (75%) defined on the basis of stimulus shape. Attended targets required a binary choice based on stimulus color. Selective attention led to the expected increase in both midlatency (N2b) and late (P3) brain potential components. Furthermore, selective attention led to increased anticipatory cardiac slowing preceding the target stimulus and to increased primary bradycardia. Correlational analyses revealed a positive relation between the effects of selective attention on N2b amplitude and primary bradycardia suggestive of cortical involvement in the chronotropic control of heart rate.

Mental fatigue and task control: planning and preparation

The effects of mental fatigue on planning and preparation for future actions were examined, using a task switching paradigm. Fatigue was induced by "time on task," with subjects performing a switch task continuously for 2 hr. Subjects had to alternate between tasks on every second trial, so that a new task set was required on every second trial. Manipulations of response-stimulus intervals (RSIs) were used to examine whether subjects prepared themselves for the task change. Behavioral measurements, event-related potentials (ERPs), and mood questionnaires were used to assess the effects of mental fatigue. Reaction times (RTs) were faster on trials in which no change in task set was required in comparison with switch trials, requiring a new task set. Long RSIs were used efficiently to prepare for the processing of subsequent stimuli. With increasing mental fatigue, preparation processes seemed to become less adequate and the number of errors increased. A clear poststimulus parietal negativity was observed on repetition trials, which reduced with time on task. This attention-related component was less pronounced in switch trials; instead, ERPs elicited in switch trials showed a clear frontal negativity. This negativity was also diminished by time on task. ERP differences between repetition and switch trials became smaller with increasing time on task.

Sentence comprehension and word repetition: a positron emission tomography investigation

Using positron emission tomography, visual presentation of sentences was shown to cause increased regional cerebral blood flow relative to word lists in the left lateral anterior superior and middle temporal gyri, attributable to cognitive processes that occur during sentence comprehension in addition to those carried out during word comprehension. Additional comparisons showed that repeating words (in a different context, when subjects did not attempt to learn the initial lists) led to significant patterns of both increased blood flow (left putamen and right caudate) and decreased blood flow (left posterior temporal lobe). Increases are argued to reflect retrieval of memory traces, whereas decreases reflect diminished necessity for processing of input. A decrease in the left inferior parietal lobe was attributable to other factors.

Cardiac adaptivity to attention-demanding tasks in children with a pervasive developmental disorder not otherwise specified (PDD-NOS)

BACKGROUND

Decreases in heart rate variability (HRV) have been repeatedly demonstrated to be an index of effort allocation to attention-demanding tasks. Children with autistic-type problems in social interaction and in adapting to unfamiliar situations (DSM-IV: PDD-NOS) have been shown to have specific attention deficits. These children were hypothesized to exhibit less cardiac adaptivity to attention-demanding tasks.

METHODS

Two groups of 18 children with PDD-NOS, judged to be hyperactive and nonhyperactive, were compared to 18 healthy children with respect to their performances on a visual attention task and the differences in HRV measured during periods of task performance and periods of rest.

RESULTS

Compared to the control group, both clinical groups were found to have a stronger capacity limitation in processing high loads of information, and to be less capable of maintaining a stable task performance throughout the whole task. Both clinical groups showed significantly less decreases in HRV during the periods of task performance. The magnitude of rest-task differences in HRV was found to correlate significantly with a behavioral measure of resistance to unexpected changes in daily routines.

CONCLUSIONS

Children with PDD-NOS are significantly less flexible in their autonomic adaptation to attention-demanding tasks. The findings are interpreted as reflecting a deficiency in the functional organization of those neural pathways that provide cortical control of the visceral efferents.

An event-related brain potential correlate of visual short-term memory

Event-related potentials (ERPs) were recorded as 12 subjects performed a delayed matching to sample task. We presented two bilateral abstract shapes and cued spatially which had to be memorized for a subsequent matching task: left, right or both. During memorization a posterior slow negative ERP wave developed over the hemisphere contralateral to the memorized shape. This effect was similar in high and low memory load trials while the memory figures were visible (for 1000 ms). As the figures disappeared (for 1500 ms), the effect persisted only in the low memory load conditions. We suggest that the contralateral negativity reflects a visual short-term memory process and that capacity limitation in the high memory load condition causes this process to collapse.

ERP effects of spatial attention and display search with unilateral and bilateral stimulus displays

Two experiments were performed in which the effects of selective spatial attention on the ERPs elicited by unilateral and bilateral stimulus arrays were compared. In Experiment 1, subjects received a series of grating patterns. In the unilateral condition these gratings were presented one at a time, randomly to the right or left of fixation. In the bilateral condition, gratings were presented in pairs, one to each side of fixation. In the unilateral condition standard ERP effects of visual spatial attention were observed. However, in the bilateral condition we failed to observe an attention related posterior contralateral positivity (overlapping the P1 and N1 components, latency interval about 100-250 ms), as reported in several previous studies. In Experiment 2, we investigated whether attention related ERP lateralizations are affected by the task requirement to search among multiple objects in the visual field. We employed a task paradigm identical to that used by Luck et al. (Luck, S.J., Heinze, H.J., Mangun, G.R., Hillyard, S.A., 1990. Visual event-related potentials index focused attention within bilateral stimulus arrays. II. Functional dissociation of P1 and N1 components. Electroencephalogr. Clin. Neurophysiol. 75, 528-542). Four letters were presented to a visual hemifield, simultaneously to both the attended and unattended hemifields in the bilateral conditions, and to one hemifield only in the unilateral conditions. In a focused attention condition, subjects searched for a target letter at a fixed position, whereas they searched for the target letter among all four letters in the divided attention condition (as in the experiment of Luck et al., 1990). In the bilateral focused attention condition, only the contralateral P1 was enhanced. In the bilateral divided attention condition a prolonged posterior positivity was observed over the hemisphere contralateral to the attended hemifield, comparable to the results of Luck et al. (1990). A comparison of the ERPs elicited in the focused and divided attention conditions revealed a prolonged 'search related negativity'. We discuss possible interactions between this negativity and attention related lateralizations. The display search negativity consisted of two phases, one phase comprised a midline occipital negativity, developing first over the ipsilateral scalp, while the second phase involved two symmetrical occipitotemporal negativities, strongly resembling the N1 in their topography. The display search effect could be modelled with a dipole in a medial occipital (possibly striate) region and two symmetrical dipoles in occipitotemporal brain areas. We hypothesize that this effect reflects a process of rechecking the decaying information of iconic memory in the occipitotemporal object recognition pathway.

Covariation of Phasic Cardiovascular and Cortical Responses

Abstract Effects of maintaining an alert state on event-related brain potentials (ERPs) and evoked cardiovascular responses were examined in an auditory detection task. Subjects were instructed to detect a possible difference in frequency between two successively presented tones in 5 s periods. Two types of trials were compared. In the first no tones were presented and subjects had to maintain an alert state for the full five seconds (uninterrupted trials). In the second type the alert state was interrupted by the presentation of visual stimuli which were presented in the second half of the 5 s period (interrupted trials). Both types of trial elicited ERPs with a negative shift consisting of a frontal and a parietal part. Uninterrupted trials elicited a stronger and longer lasting negative shift. This difference was maximal at parietal sites. The stronger negative shift was accompanied by a stronger deceleration in the heart rate response, which started at about the same time as the cortical effect but lasted somewhat longer. Furthermore, uninterrupted trials evoked a stronger decrease in the blood pressure response. This effect showed the expected delay when compared to the effect on heart rate (HR). The cardiovascular data confirmed the hypotheses concerning effects of maintaining an alert state, but the cortical data partly contradicted them. Altogether, the current findings do not contradict an active network involved in alertness, but they do not confirm the expected stronger involvement of the right hemisphere and involvement of prefrontal areas in this function.

Priming and aging: an electrophysiological investigation of N400 and recall

Twenty young (20.5 years) and 20 middle-aged academics (57.2 years) performed a priming-recall task which was presented in three blocks. In each block, participants read 40 word pairs after which a recall task had to be carried out. Half of the word pairs were highly associated while the others were low associated. Targets showed the N400 of the middle-aged group to be both delayed and smaller in amplitude for low-associated items. N400 of primes, however, showed no age-related latency difference but was smaller for the middle-aged group due to a positive shift. It is argued that this shift possibly indicates age differences in semantic activation or buildup of context. A reanalysis showed individual differences in word pair processing to depend on recall performance. In general, high recallers were found to show a much larger differentiation between low- and high-associated targets. This resulted from a much larger N400 component elicited by low-associated targets and a more positive ERP in the N400-region for the high-associated targets. It is suggested that the middle-aged subjects activated the expected target word to a level at least equivalent to the younger subjects, but that the activated network itself was larger/less selective particularly in subjects showing a low recall.

Localizing components of a complex task: sentence processing and working memory

Three areas of the left hemisphere play different roles in sentence comprehension. An area of posterior middle and superior temporal gyrus shows activation correlated with the structural complexity of a sentence, suggesting that this area supports processing of sentence structure. The lateral anterior temporal gyrus is more activated bilaterally by all sentence conditions than by word lists; thus the function of the area probably does not directly support processing of structure but rather processing of words specific to a sentence context. Left inferior frontal cortex also shows activation related to sentence complexity but is also more activated in word list processing than in simple sentences; this region may thus support a form of verbal working memory which maintains sentence structural information as well as lexical items.

Influence of respiratory activity on the cardiac response pattern to mental effort

A group of 32 healthy adult volunteers completed three blocks of a reaction time task that varied in the degree of controlled processing load. A rest period preceded each of the task blocks. The task blocks were presented in the order of either increasing or decreasing cognitive load. For each of the six periods, mean values and spectral measures of heart rate and respiration variability were calculated. The spectral measures were obtained for three different frequency bands. Differences between the cardiac measures of the task and preceding rest periods were compared with respect to differences in task load and the order of task presentation. All comparisons were carried out while adjusting for respiratory variability in the corresponding frequency band. The frequency band in which task load-related changes in heart rate variability became manifest appeared to be dependent on the individual's breathing pattern.

Color selection and location selection in ERPs: differences, similarities and 'neural specificity'

It was hypothesized that color selection consists of two stages. The first stage represents a feature specific selection in neural populations specialized in processing color. The second stage constitutes feature non-specific selections, related to executive attentional processes and/or motor processes. This hypothesis was tested by investigating the effects of selectively attending to a specific color, location, or conjunction of location and color on the ERPs elicited by briefly flashed gratings. The gratings differed on three dimensions: color (red or blue), location in the visual field (4.4 degrees to the left or right of fixation) and form (target or non-target). Subjects had to respond to the presentation of target gratings in the attended category. Color selection was reflected in an enhanced parietal positivity in the 150-190 ms interval. Source analyses suggested that this color selection positivity might be generated in the basal occipital cortex, possibly human V4, an area of the brain specialized in color processing. The effect was separated from the P1 spatial attention effect both in topography and sources. Color selection was also reflected in a contralateral occipitotemporal negativity, which resembled the N1 spatial attention effect both in timing and topography. And finally, color selection was reflected in an N2b component. This N2b was similar in timing, topography and sources to the N2b's elicited by location selection and conjunction selection. We suggested that the N2b reflects feature non-specific selection processes, elicited by a range of attended stimuli, and possibly reflects activity in the anterior cingulate cortex. The NP80 was unaffected by attention to color and/or location and localized in striate cortex.

When syntax meets semantics

Three experiments concerning the processing of syntactic and semantic violations were conducted. Event-related potentials (ERPs) showed that semantic violations elicited an N400 response, whereas syntactic violations elicited two early negativities (150 and 350 ms) and a P600 response. No interaction between the semantic and early syntactic ERP effects was found. Sentence complexity and violation probability (25% vs. 75%) affected only the P600 and not the early negativities. The probability effect was taken as evidence that the P600 resembles the P3b. The temporal order of word processing in a sentence as suggested by the data was such that a more automatic syntactic analysis was performed (earlier syntactic-related negativities) in parallel with a semantic analysis (N400), after which a syntactic reanalysis was performed (P600). A reanalysis interpretation of the P600 could explain why the extent of the reanalysis differed with syntactic complexity and probability of ungrammaticality.

Evoked heart rate and blood pressure in an S1-S2 paradigm

Phasic changes in heart rate (HR) and blood pressure (BP) in an S1-S2 paradigm were studied in three experiments. In each experiment, a memory search task was performed at S1. The outcome of this task indicated whether a fast or a delayed response had to be given after S2. Besides this response instruction, there were two other task manipulations: in one experiment the memory load at S1 was varied, whereas in each experiment a different kind of performance feedback was given. Both HR and BP showed a triphasic pattern, consisting of an initial decrease, followed by an increase and another decrease. The BP patterns were quite consistent, and delayed a few seconds relative to the HR pattern. The memory load manipulation at S1 showed that the changes early in the S1-S2 interval (initial decrease and subsequent increase) reflect the processing of S1. The effects of response instruction showed that the second HR deceleration, and the subsequent BP decrease, reflect the preparation of the motor response. In Experiment 2 the level of the evoked HR and BP pattern was shifted as a function of the type of reward (a bonus or noise).

An ERP study of visual spatial attention and letter target detection for isoluminant and nonisoluminant stimuli

The event-related potential (ERP) effects of visual spatial attention and letter target detection for stimuli presented against a (nonisoluminant) dark background or against an isoluminant grey background were investigated. The goal was to study how the perceptual variable of luminance would influence early ERP reflections of selective attention. Such effects could further substantiate the claim that selective attention operates at the level of early perceptual processing and could provide evidence regarding the role of different visual routes in selective attention. Isoluminance increased the peak latency of the early ERP deflections (NP80, P1, and N1) by 40-50 ms. The ERP effects of spatial attention, consisting of P1 and N1 amplitude enhancements, were similarly delayed by isoluminance, supporting the idea that early selective processing is strongly dependent on bottom-up perceptual processing. P300 latency and reaction time were delayed by 70-75 ms, the additional delay probably reflecting that isoluminance affected decision processes in addition to perceptual processes. Isoluminance left the scalp topographies of the early ERP deflections largely unaffected, although a slight shift of the N1 topography in the isoluminant condition toward more inferior lateral posterior regions of the scalp could have reflected an increased contribution from ventral (occipitotemporal) brain areas. Relative to nontarget letters, targets presented at both attended and unattended spatial positions elicited an early contralaterally dominant lateral occipitotemporal negativity (N2pc). This ERP component is proposed to reflect an early, partly automatic process of template matching, consistent with indications from spatiotemporal dipole modelling that the N2pc was generated in inferior occipitotemporal brain regions.

Heart rate variability in patients with atrial fibrillation is related to vagal tone

BACKGROUND

Analysis of heart rate variability (HRV) has thus far not been applied in patients with atrial fibrillation, probably because of the presumed absence of any form of patterning of the ventricular rhythm, particularly vagally mediated respiratory arrhythmia. However, such patterning is theoretically conceivable given the function of the atrioventricular node in atrial fibrillation and its susceptibility to autonomic influences.

METHODS AND RESULTS

Sixteen patients (mean age, 56+/-4 years) with long-term atrial fibrillation on fixed doses of digoxin or verapamil were studied; 12 healthy men in sinus rhythm were used as control subjects. HRV (standard deviation of RR intervals [SD], coefficient of variance [CV], the root-mean-square of successive difference [RMSSD], and low-frequency [LF] and high-frequency power [HF]) was analyzed during 500 RR intervals at baseline, after administration of propranolol (0.2 mg/kg I.V.), and after subsequent administration of methylatropine (0.02 mg/kg I.V.). HRV at baseline and changes in HRV after methylatropine were then related to vagal tone (vagal cardiac control), quantified as the decrease in mean RR after methylatropine. Baseline HRV was higher in the atrial fibrillation group than in the control group; after propranolol, HRV increased in both groups; after methylatropine, HRV neared zero in the control group, whereas it returned to baseline values in the atrial fibrillation group. SD, RMSSD, LF, and HF at baseline were significantly (P<.05) correlated with vagal tone in the control group but also in the atrial fibrillation group (correlation coefficients of .60, .61, .57, and .64, respectively). Even stronger correlations were observed between changes in these parameters after methylatropine and vagal tone, particularly in the atrial fibrillation group (correlation coefficients of .89, .87, .72, and .90, respectively).

CONCLUSIONS

This study shows that HRV in patients with atrial fibrillation is related to vagal tone.

Covariation of phasic cortical and cardiovascular responses in a detection task

The relationship between cardiovascular and cortical responses was examined in an experiment in which subjects performed a detection task and a simple reference task. The detection task was developed according to Skinner et al., (1987). Cortical activity was examined with event related brain potentials (ERPs). ERPs revealed more cortical activation during detection task blocks. Both tonic and phasic measures of cardiovascular activity were derived. Tonic measures were heart rate (HR), systolic blood pressure (SBP). T-wave amplitude (TWA), respiration linked HR-variability and a measure for baroreflex sensitivity. These measures revealed no important differences between the reference task and detection task blocks. Phasic cardiovascular measures were evoked HR, SBP and TWA. Evoked HR showed a larger deceleration and evoked SBP showed a smaller decrease on detection task blocks. Evoked TWA did not differentiate between both types of task. It is concluded that an adjusted version of the fronto-cortical control hypothesis of Skinner could best account for the data.

A psychophysiological investigation of the selection and the use of partial stimulus information in response choice

Two alternative explanations were examined for why selective response activation sometimes starts before stimulus identification is complete (e.g., J. O. Miller & S. A. Hackley, 1992) and sometimes starts only after stimulus identification is complete (e.g., R. De Jong, M. Wierda, G. Mulder, & L. J. M. Mulder, 1988). Distinct psychophysiological methods related to stimulus identification and response selection provided evidence suggesting that partial stimulus information is identified but is or is not used before the stimulus is identified more fully, depending on task requirements. This result (a) suggests strategic adaptation of task performance, (b) is inconsistent with particular discrete and continuous models of information processing, and (c) shows the existence of a central selection mechanism that can prevent the automatic activation of responses associated with preliminary available stimulus information.

Acute effects of caffeine on selective attention and visual search processes

The influence of a single dose of caffeine was evaluated in focused and divided attention conditions of a visual selective search task in which subjects had to perform controlled search processes to locate a target item. Search processes were manipulated by varying display load. A dose of 3 mg/kg body weight caffeine or lactose, dissolved in a cup of decaffeinated coffee, was administered double blindly and deceptively to overnight abstinent coffee drinkers. Behavioral measures were supplemented by event-related potentials (ERPs). Subjects reacted faster in the caffeine condition. The P3b peak latency decreased after caffeine in the low display load condition and in the focused attention condition, indicating that the effects of caffeine are dependent on the number of relevant display items, not on the total number of display items presented. Search processes, as reflected in a negative ERP deflection, were not affected by caffeine.

Focussing on aging: an electrophysiological exploration of spatial and attentional processing during reading

Three types of selective attention tasks were presented to 24 young (20.5 years) and 24 middle-aged (57.5 years) participants. The major aim of the experiment was to explore three different aspects of selective attention, namely a pre-attentive level (i.e. auditory passive oddball task), an attentive level using spatial attention in a memory search task (i.e. selective search task) and an attentive level using a spatial cue to select a word in a reading-like situation (i.e. selective language task). The data showed that the mismatch negativity was not affected by aging although the ERPs indicated that the younger participants were paying more attention to the tones than the middle-aged. The selective search task data showed that spatial selective attention is only mildly affected by aging. The ERP-data seemed to indicate that irrelevant stimuli had a smaller impact in the middle-aged. The selective language data showed a look-a-like effect of flanker words for both age groups although the effect in the middle-aged was delayed by 30 ms and smaller. It was theorized that flankers might have smaller impact in the middle-aged. N400 was found to be smaller and delayed (90 ms) in the middle-aged participants. The overall conclusion on the basis of the three experiments is that the selectivity of processing was preserved or even enhanced in our particular group of middle-aged participants.

A psychophysiological investigation of the selection and the use of partial stimulus information in response choice

Two alternative explanations were examined for why selective response activation sometimes starts before stimulus identification is complete (e.g., J. O. Miller & S. A. Hackley, 1992) and sometimes starts only after stimulus identification is complete (e.g., R. De Jong, M. Wierda, G. Mulder, & L. J. M. Mulder, 1988). Distinct psychophysiological methods related to stimulus identification and response selection provided evidence suggesting that partial stimulus information is identified but is or is not used before the stimulus is identified more fully, depending on task requirements. This result (a) suggests strategic adaptation of task performance, (b) is inconsistent with particular discrete and continuous models of information processing, and (c) shows the existence of a central selection mechanism that can prevent the automatic activation of responses associated with preliminary available stimulus information.

Cultured skin as a 'smart material' for healing wounds: experience in venous ulcers

The healing of chronic wounds is a difficult and varied problem. The engineering of a cultured skin tissue offers an adaptive therapy for chronic wounds. Our hypothesis has been that living tissue can act as a 'smart material' to heal wounds. We have examined the healing characteristics of a bilayered cultured skin equivalent (Graftskin) in a controlled study and present clinical data from interim analyses for 233 patients over 6 months of treatment. All venous ulcer patients will be followed for up to 1 year. We report on three basic scenarios of healing: (i) promotion of healing by secondary intention, (ii) persistent biological wound closure with stimulation of underlying healing, and (iii) healing by frank graft take of the cultured material with remodelling of the tissue over time. Our results indicate that the cultured skin equivalent is responsive to individual wound conditions and thus acts as a 'smart material' in the chronic wound.

Evaluation of importance of central effects of atenolol and metoprolol measured by heart rate variability during mental performance tasks, physical exercise, and daily life in stable postinfarct patients

BACKGROUND

Physical exercise and mental work cause alterations in cardiac autonomic control. beta-Blockers protect the heart against stress, and this effect may be in part centrally mediated. In this context, the lipophilicity of the drug would be clinically relevant.

METHODS AND RESULTS

Thirty postinfarct patients were randomized to receive 100 mg atenolol or 200 mg metoprolol CR in a double-blind, crossover manner, each for a 6-week period. Heart rate (HR) variability was used to study autonomic effects during mental and physical stress and to study circadian variations. Mean 24-hour HR decreased from 77 +/- 7 to 60 +/- 6 beats per minute after atenolol and to 62 +/- 6 beats per minute after metoprolol (P = .046). At baseline, mental performance tasks did not affect HR, but decreased HR variability (SDNN index from 51 +/- 26 to 30 +/- 13 milliseconds [ms], P < .001; high-frequency power from 130 +/- 143 to 110 +/- 125 ms2, P = .046; and low-frequency power from 538 +/- 447 to 290 +/- 275 ms2, P < .001). Both beta-blockers decreased HR during mental performance tasks (P < .001) and increased SDNN index and high-frequency power. Before treatment, bicycle exercise decreased HR variability; root-mean-square of successive difference decreased from 21 +/- 8 to 15 +/- 10 ms (P = .004). beta-Blockade could not prevent this decrease. No differences between atenolol and metoprolol were observed for absolute high- and low-frequency power or after adjustment for HR. Vagal blockade with methylatropine during chronic beta-blocker treatment nearly abolished all components of spectral power. HR was found to be the parameter most strongly affected by beta-blockade but not by an influence on vagal tone. No differences were found between atenolol and metoprolol.

CONCLUSIONS

In stable postinfarct patients, chronic treatment with metoprolol and atenolol attenuates the reduction in HR variability induced by mental performance tasks, but the effects during exercise are limited. beta-Blockers do not appear to increase vagal tone in this stable patient group. The point of action in these patients is mainly a reduction in HR, probably due to a reduction in stress-induced sympathetic activation. Clinically significant differences between atenolol and metoprolol were absent, indicating that the degree of lipophilicity does not distinguish among the beta-blockers what their salutary effects are on HR variability during the specific challenges used.

The availability versus the use of partial information: multiple levels of selective processing between perception and action

Temporal overlap of cognitive processes occurs when partial information about a stimulus activates associated responses before the stimulus has been fully identified. Recent evidence obtained with psychophysiological measures suggests that such overlap sometimes does, and sometimes does not occur. In this contribution, we argue that in order to understand why, we have to distinguish between selection of partial information for perception and selection of partial information for control over activation of responses. We discuss several mechanisms and factors that may modulate the temporal overlap of mental processes because they selectively influence the perceptual availability or the use of partial information.

The role of neuroimaging in the discovery of processing stages. A review

In this contribution we show how neuroimaging methods can augment behavioural methods to discover processing stages. Event Related Brain Potentials (ERPs), Brain Electrical Source Analysis (BESA) and regional changes in cerebral blood flow (rCBF) do not necessarily require behavioural responses. With the aid of rCBF we are able to discover several cortical and subcortical brain systems (processors) active in selective attention and memory search tasks. BESA describes cortical activity with high temporal resolution in terms of a limited number of neural generators within these brain systems. The combination of behavioural methods and neuroimaging provides a picture of the functional architecture of the brain. The review is organized around three processors: the Visual, Cognitive and Manual Motor Processors.

Aging, caffeine, and information processing: an event-related potential analysis

Structural and energetic processes in information processing were studied in young and elderly subjects. A visually focussed selective search task was used, in which subjects had to select relevant information, followed by controlled memory search processes to locate a target item. Caffeine was used to manipulate the energetic state of the subjects. During task performance event-related potentials (ERPs) and reaction time (RT) were recorded. Subjects were 15 young and 15 elderly healthy, non-smoking, moderate caffeine consumers (250-600 mg/day). Before the experimental sessions they abstained from caffeine for > or = 12 h. In the experiment subjects received 250 mg caffeine or placebo dissolved in decaffeinated coffee. RT data seem to indicate that aging effects are at least partly due to a shift in the speed-accuracy trade-off. ERP results provide evidence for decreased levels of energy resources in the elderly. The identification of relevant information and stimulus evaluation processes were delayed in the elderly, suggesting an additional effect of aging on structural processes. Caffeine improved performance and increased the amplitude of the N1, N2b, and P3b, in both young and old subjects. These results suggest that caffeine makes more energy resources available for task performance. The effects of aging on P3b latency were counteracted by caffeine. Other caffeine effects did not differ significantly between young and elderly subjects.

The effectiveness of dry bed training for nocturnal enuresis in adults: a 3, 5, 6 years follow-up

Nine enuretic adults who had been successfully treated by a minimal contact Dry Bed Training (DBT) were followed-up after 3, 5, and 6 years. During the follow-up period there has been substantial relapse: 5 out of 9 remaining continent throughout the whole period but 4 relapsing. However after 6 yr eight of them were continent: be it after pharmacological therapy (n = 1), after a booster training (n = 1). As most of the Ss were primary enuretics it is concluded that minimal intervention DBT is a significant contribution to the cure of nocturnal enuresis in adults.

Language, memory, and aging: an electrophysiological exploration of the N400 during reading of memory-demanding sentences

Twenty-four young and 24 middle-aged academics carried out a language recognition task in which sentences were presented that made either a high or a low demand on working memory (WM). The sentences ended either normally (i.e., congruent) or with an incongruous word. Middle-aged subjects had smaller WM scores, a marginally slowed down recognition performance, and a smaller and delayed N400 component. The event-related potential (ERP) difference between congruent and incongruent endings was smaller in the high-load condition for younger subjects and totally disappeared for the middle-aged subjects. ERPs for all subjects showed a WM-related positivity in the middle of the sentence and a WM-related negativity at the sentence ending. These shifts could be associated with either storage and retrieval processes or with clause wrap-up processes. Most ERP-effects were dependent on WM capacity. Age differences in sentence processing are not simply explained by age itself but depend to a large extent on individual memory capacity.

Influence of caffeine on selective attention in well-rested and fatigued subjects

Effects of caffeine were studied in a visual focused selective search task in well-rested and fatigued subjects. A dose of 200 + 50 mg caffeine or placebo, dissolved in decaffeinated coffee, was administered in a double-blind and deceptive fashion. The task was to detect a target letter on one diagonal of a visual display designated as relevant and ignore stimuli presented on the irrelevant diagonal. Behavioral measures were supplemented by event-related potential (ERP) measures. Subjects reacted faster in the caffeine condition. Caffeine enhanced the N1 and the N2b components. Selection of relevant information apparently was more adequate in this condition. Search negativity was not affected by caffeine. Caffeine effects on the P3 elicited by target letters were more pronounced in the fatigued than in the well-rested subjects, indicating that the effects of caffeine are dependent on the state of the subject. The results suggest that caffeine has specific rather than general effects on information processing.

Focusing on the N400: an exploration of selective attention during reading

In a series of two experiments, subjects read sentences wherein words were flanked in the lower visual field by irrelevant words (i.e., flankers). The visual angle between the words in the sentence and the flanker words was manipulated (i.e., 0.57 degrees, 0.97 degrees, 1.37 degrees). Sentence endings were either congruent or incongruent; incongruent endings elicited a large N400 component. Flanker effects were observed for sentence final words on electrophysiological measures during the reading task and on subsequent recognition memory performance for sentence final and new words. For both measures, the flanker effect interacted with the congruency of the sentence ending as well as the visual angle between the sentence final word and its flanker. The largest and earliest flanker effects were observed for congruent endings at the smallest visual angle (0.57 degrees); congruent endings and flankers in intermediate visual angle (0.97 degrees) conditions displayed a similar flanker-related negativity but with a longer onset latency (490 vs. 280 ms). Congruent endings and their flankers in the largest visual angle (1.57 degrees) conditions revealed no flanker effect.

Visual spatial attention to stimuli presented on the vertical and horizontal meridian: an ERP study

In the first experiment, 48 subjects carried out a visual spatial attention task. Stimuli were presented at the vertical meridian, either above or below a fixation dot, and the subjects were instructed to attend to one of these stimulus positions and ignore the other position. In three different conditions, the distances between stimulus positions and fixation were 0.5 degrees, 0.9 degrees, and 1.3 degrees. Subjects searched for the presence of prememorized target letters at the attended location: memory load was one or four items in different conditions. The P1/N1 enhancement typically found on the horizontal dimension was not observed on the vertical dimension. Instead, a positive shift of the attended compared with the unattended stimuli was found, which was most prominent at anterior electrodes. This positivity showed effects of the distance manipulation. The N2b-P3a effects of attention and the effect of memory load (search negativity) normally present in this kind of selective search task were also found. Reaction times were faster when attention was directed above fixation than when it was directed below fixation. The event-related potential data suggested that this difference could be attributed to a more efficient neglecting of irrelevant stimuli presented below fixation. In Experiment 2, we examined whether the absence of the P1/N1 enhancement as the result of spatial attention in Experiment 1 could be attributed to (a) the presentation of stimuli along the vertical meridian instead of along the horizontal meridian, (b) the use of midline electrodes instead of lateralized electrodes, and (c) the relatively small spatial separation between the relevant and irrelevant stimuli. Twelve subjects searched for the presence of a single target letter at an attended position in three different conditions. In two of the conditions the letters were presented to the left or right of fixation. The distance between fixation and the stimulus positions was 1.3 degrees in one of these conditions and 3 degrees in the other condition. In the third condition, the stimuli were presented at 3 degrees above or below fixation. In all three conditions effects similar to those in Experiment 1 were observed. In addition, in all three conditions an enhancement of the P1 and N1 components was found at two lateral occipitotemporal electrodes.

Effects of lorazepam on cardiac vagal tone during rest and mental stress: assessment by means of spectral analysis

Dose-dependent effects of intravenously administered lorazepam on haemodynamic fluctuations were studied by means of spectral analysis, in order to elucidate sympathetic and parasympathetic components in cardiovascular control during situations of rest and mental stress after benzodiazepine administration. In a double-blind randomized cross-over study, nine male volunteers participated in two sessions: a placebo and lorazepam session. During these sessions, the subjects repeatedly performed a 10-min version of the Stroop Color Word Test (CWT), with 10 min of rest between the CWTs. Lorazepam was administered before each rest period in increasing doses of 0.0, 0.06, 0.13, 0.25 and 0.5 mg (total cumulative dose: 0.94 mg). During the placebo session the subjects received five placebo injections. For five of the nine subjects the lorazepam session was their first session. Heat rate (HR), blood pressure (BP) and respiration were recorded continuously. Power spectra were calculated per 2.5-min periods for HR, systolic (SBP) and diastolic BP (DBP). Spectral density was assessed for three frequency bands: low (LFB: 0.02-0.06 Hz), mid (MFB: 0.07-0.14 Hz) and high (HFB: 0.15-0.40 Hz). During the consecutive periods of rest, lorazepam induced a dose-dependent decrease in HR, and a dose-dependent increase in LFB, MFB and HFB power of HR, but lorazepam had no effect on BP. The effects were significant after 0.44 mg lorazepam for HR and HFB power, and after 0.94 mg lorazepam for the HR fluctuations in the LFB and MFB. Lorazepam did not influence the cardiovascular responses to the CWT.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

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.

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.

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.