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Biomedical subjects

P Ullsperger

Publications and source records attributed to P Ullsperger.

At least 19 recordsLinked to original sources
PubMed2001

Auditory probe sensitivity to mental workload changes - an event-related potential study.

The goal of this study was to explore the utility of parameters of ERPs for assessment of mental workload during performance of complex tasks. In addition to a baseline auditory oddball task, 15 healthy adult volunteers performed gauge monitoring (Gauge) and mental arithmetic (Math) separately and together. Throughout the task performance three types of auditory stimuli were presented as probes, i.e. 80% 1000 Hz tones, 10% 2000 Hz tones and 10% novel sounds. The ERP components N1 and P3 were analysed, which are assumed to reflect perceptive and central processing resources. The results interpreted in the framework of capacity theory indicate high demand on processing resources already during separate performance of both tasks Gauge or Math. During simultaneous performance the workload on average exceeded the limits of processing capacity: the performance data impaired significantly. The ERP measures N1 and P3 were confirmed in their sensitivity and diagnosticity. By using novel sounds as probes with involuntary attention-capturing properties, one might overcome a problem of the irrelevant probe technique, i.e. whether the operator spends his spare capacity for processing of the irrelevant probes.

Acoustic Stimulation↗
PubMed2000

Event-related potentials in a self-paced novelty oddball task.

The event-related potentials (ERPs) to the stimuli triggered by a participant's self-paced key press were compared with the ERPs to the same stimuli presented at an external pace. Fourteen participants responded to 2000 Hz target tones interspersed among 1000 Hz standard tones and various unique novel sounds. The amplitudes of the P3s elicited by target and novel stimuli were larger in the self-triggered condition than in the machine-triggered condition in which the stimuli were presented automatically with the same intervals as in the self-triggered condition. The effect was prominent at fronto-central scalp sites. When the timing of stimulus is unequivocal, a neural activity related to stimulus evaluation may increase and manifest itself as a large late positive ERP component.

Acoustic Stimulation↗
PubMed2000

Microwaves emitted by cellular telephones affect human slow brain potentials.

The influence of electromagnetic fields (EMF) emitted by cellular telephones on preparatory slow brain potentials (SP) was studied in two experiments, about 6 months apart. In the first experiment, a significant decrease of SP was found during exposure to EMF in a complex visual monitoring task (VMT). This effect was replicated in the second experiment. In addition to the VMT, EMF effects on SP were analysed in two further, less demanding tasks: in a simple finger movement task to elicit a Bereitschaftspotential (BP) and in a two-stimulus task to elicit a contingent negative variation (CNV). In comparison to the VMT, no significant main EMF effects were found in BP and CNV tasks. The results accounted for a selective EMF effect on particular aspects of human information processing, but did not indicate any influence on human performance, well-being and health.

Adult↗
PubMed1999

EEG power changes during a multiple level memory retention task.

EEG changes related to the amount of information held in memory during a 4-s retention period were studied. The predictability of the amount of information held in memory was varied. In the weighted condition, 60% of the trials contained only one item and the remaining 40% of the trials were evenly distributed between trials containing 3, 5, 7, or 8 items. In the random condition, the levels were equally represented and randomly presented. In the blocked condition the levels were equally represented but presented in five blocks containing only items from one of the levels. Initial widespread decreases in alpha band power were followed by increased activity in all three conditions. The more difficult of the five levels produced decreased alpha activity in more localized posterior left hemisphere sites. This suggests two alpha mechanisms, one associated with task engagement and the other related to the cognitive demands regardless of the presentation context. Theta band power increased over frontal scalp, and to a lesser extent over left parietal and temporal areas and bilateral occipital sites, during only the weighted condition. These changes were uniform over the entire retention period. Beta 2 activity was also influenced by the task difficulty and the time course of the retention period in the two conditions. Beta 2 activity resembled both alpha and theta in that in levels 1, 2 and 3 it acted like alpha with increasing power over time at numerous widespread sites while the higher difficulty levels showed higher power at the beginning of the retention period and then decreased.

Adolescent↗
PubMed1999

Slow brain potentials in a visual monitoring task.

The purpose of this study was to analyse slow brain potentials (SPs) during visual monitoring, needed to perform the clock-monitoring task (CMT). This task was successfully applied in behavioural studies, in which attention capabilities were investigated in dependence on individual factors. Clearly pronounced preparatory SPs were observed during the CMT reflecting a high level of preparation and attention, necessary for achieving high performance accuracy. The well-known influence of task repetition on SPs and the relation between SP and behaviour were confirmed. The practicability of the CMT, the clear and easily detectable SP components and the sensitivity of the present approach makes it recommendable for further applications, e.g. for the evaluation of the effects of occupational/environmental exposures on processes of information processing.

Adult↗
PubMed1999

Event-related potential correlates of individual differences in working memory capacity.

The capacity of working memory has been suggested to differ among people and these differences affect performance in a wide variety of cognitive tasks. This study explored electrophysiological correlates of individual differences in working memory capacity by means of event-related potentials. Thirty-four healthy students performed two- and five-choice reaction time tasks. In the two-choice reaction time (2CRT) task, two digits (3 and 7) were presented visually with probabilities of .20 and .80. In the five-choice reaction time (5CRT) task, five digits (3, 4, 5, 6, and 7) were presented equiprobably in a random order. Participants were required to press a button corresponding to each digit with a different finger. Working memory capacity of each participant was assessed by the reading span test originated by M. Daneman and P.A. Carpenter (1980). Participants with high reading span produced larger P300s than did persons with low reading span in the 5CRT task, but the difference was not significant in the 2CRT task. It had been suggested that individual differences in working memory capacity would affect initial stages of information processing as early as 300 ms after stimulus onset.

Adult↗
PubMed1998

Mobile phones modulate response patterns of human brain activity.

Mobile phones emit a pulsed high-frequency electromagnetic field (PEMF) which may penetrate the scalp and the skull. Increasingly, there is an interest in the interaction of this pulsed microwave radiation with the human brain. Our investigations show that these electromagnetic fields alter distinct aspects of the brain's electrical response to acoustic stimuli. More precisely, our results demonstrate that aspects of the induced but not the evoked brain activity during PEMF exposure can be different from those not influenced by PEMF radiation. This effect appears in higher frequency bands when subjects process task-relevant target stimuli but was not present for irrelevant standard stimuli. As the induced brain activity in higher frequency bands has been proposed to be a correlate of coherent high-frequency neuronal activity, PEMF exposure may provide means to systematically alter the pattern fluctuations in neural mass activity.

Acoustic Stimulation↗
PubMed1998

Effects of microwaves emitted by cellular phones on human slow brain potentials.

The influence of electromagnetic fields (EMF) emitted by cellular phones on preparatory slow brain potentials (SP) was studied in two different experimental tasks: In the first, healthy male human subjects had to perform simple self-paced finger movements to elicit a Bereitschaftspotential; in the second, they performed a complex and cognitive demanding visual monitoring task (VMT). Both tasks were performed with and without EMF exposure in counterbalanced order. Whereas subjects' performance did not differ between the EMF exposure conditions, SP parameters were influenced by EMF in the VMT: EMF exposure effected a significant decrease of SPs at central and temporo-parieto-occipital brain regions, but not at the frontal one. In the simple finger movement task, EMF did not affect the Bereitschaftspotential.

Brain↗
PubMed1998

ERP components elicited in response to warning stimuli: the influence of task difficulty.

A series of experiments were conducted to systematically evaluate the relative contributions of task difficulty and stimulus probability to P300 amplitudes. Scalp event-related potentials (ERPs) were recorded and the topographic distributions were evaluated during a multi-level cognitive task with an antecedent warning. In three separate studies, task difficulty (five levels), probability or expectedness (10-60%), and randomness (random or blocked presentation) were manipulated. Response accuracy, subjective ratings, and reference-free averages of the P300 components elicited by the warning stimuli were evaluated. Statistical analysis indicated that significantly larger P300s were associated with the more difficult task warnings except when memory tasks were presented in a blocked design, suggesting that neither task difficulty nor probability alone can account for variations in the P300 in a multi-level task scenario. Results are discussed with regard to adaptation-level theory.

Adolescent↗
PubMed1995

The P300 to novel and target events: a spatiotemporal dipole model analysis.

It has been reported that frontal lobe structures are critical for the generation of P300 activity in the human event-related potential (ERP) evoked by novel events. In this study spatial-temporal dipole model analyses were employed to obtain further evidence on the temporal dynamics and the approximate location of neuronal activity involved in P300 generation for target and novel events. A triple dipole configuration was found to describe the scalp recorded P300 activity for novel and target events with less than 2.5% residual variance. For the novel, but not the target dipole configuration a frontally oriented dipole was obtained whose temporal activity function suggests that the brain areas involved in the processing of novel events are engaged about 70 ms earlier than those relevant for target processing.

Analysis of Variance↗
PubMed1995

Processing of multi-dimensional stimuli: P300 component of the event-related brain potential during mental comparison of compound digits.

This study explored the processing of multi-dimensional stimuli during mental comparisons by means of behavioral and event-related potential (ERP) measures. As multidimensional stimuli served compound digits with separable physical and semantic dimensions, each graduated in size. Fourteen adult volunteers were presented with the digits zero through nine, which were constructed by suitably arranged small digits of the same number set. The subject's task was to decide whether the physically larger digit was numerically larger or smaller than the physically smaller one. Large and small numbers as well as the numerical differences between them appeared, equiprobably, in randomized order. Reaction time (RT), frequency of errors, and ERPs registered from Fz, Cz and Pz (time constant 5.00 s; 30 Hz frequency cut off) were selectively averaged according to three dimensions (i) the numerical differences between simultaneously presented large and small digits, (ii) the 10 physically large digits, and (iii) the 10 physically small digits. As a reflection of the symbolic distance effect, the mean RTs and errors decreased and the P300 amplitude increased with increasing differences between the numbers compared. The P300 amplitude changed in a U-shaped function of the numerical value of the physically large digits. This result is in accordance with the adaptation-level hypothesis and indicates that prior to numerical comparisons the physically large numbers were primarily encoded and arranged into the internal number scale. The fact that the U-shaped amplitude trend was found for the physically large but not for the physically small digits is interpreted as an expression of the advantage of global information. The approach of separation task-relevant stimulus dimensions on the basis of P300 changes is proposed as an informative method for the study of multi-dimensional-stimulus processing in multi-task environments.

Adult↗
PubMed1994

Mental comparison of visually presented two-digit numbers: a P300 study.

Comparison processes were investigated in a multiple-stimulus paradigm with a pseudo-random sequence of visually presented numbers 11 to 20. The subjects' task was to compare each current number with the preceding one and to indicate whether it was larger or smaller. ERPs were selectively averaged for the 10 number stimuli, for three functional conditions according to the information the numbers provide about the ensuing response and for the differences between consecutive numbers. P300 amplitude averaged for each number stimulus showed a U-shaped trend with largest amplitudes for the numbers 11 and 20. It was found that P300 amplitudes change with the amount of information the current number is delivering for the ensuing response. This information delivery is related to the processing in the subsequent trial, as revealed by a negative correlation between P300 in the current trial and RT in the ensuing trial. Reaction times decreased significantly with increasing difference between the current number and the preceding one. This symbolic distance effect was not found for P300 parameters. The dissociation between RT and P300 data provides evidence for the assumption that under the present experimental conditions informational transaction leading to the distance effect occur after the elicitation of P300.

Adult↗
PubMed1994

Event-related potentials indicate information extraction in a comparative judgement task.

Event-related potentials (ERPs) were recorded from normal subjects in a serial paired-comparison task with the spoken digits one to five. For each digit, the subject decided whether it was smaller or larger than the preceding one. We examined to what extent ERP components are associated with the probability information each digit provides with respect to the subsequent response. Shortest reaction time (RT) and highest accuracy was obtained for the two end terms one and five. The N1 and P2 components of the ERP were attenuated for the two end terms. Three late positivities were found: early P3, P3b, and slow wave. P3b increased in amplitude the more information the eliciting digit provided with respect to the response to the subsequent digit. Moreover, a negative correlation was found between the P3b amplitude associated with information extraction and the RTs to the subsequent digit. During comparative judgement, subjects process the relative position of a stimulus within a stimulus set to extract information about the probability of a forthcoming response, and this process is reflected in P3b amplitude.

Adult↗
PubMed1993

Mental comparison: P300 component of the ERP reflects the symbolic distance effect.

The symbolic distance effect was studied in a numerical comparison task by means of behavioural measures and event-related potentials (ERP). Two numbers in the range from 11 to 20 were presented simultaneously and the subjects had to indicate if the right side number was smaller or larger than the left side number. Reaction time, error rate and ERPs were selectively averaged according to the numerical differences between the two numbers. The symbolic distance effect was confirmed: Reaction times and error rates decreased significantly with increasing difference between the two numbers. A significant distance effect was also found for both P300 amplitude and latency. The larger the numerical difference the larger the P300 amplitude and the P300 latency tended to be shorter. This finding suggests that the numerical difference is effective already during stimulus encoding.

Adult↗
PubMed1993

P3 varies with stimulus categorization rather than probability.

We examined the relationship between P3 amplitude elicited by different auditory task stimuli and response-defined categorization requirements. Two experiments were conducted which examined the effects of the categorization of tone pitches (experiment 1) and spoken digits (experiment 2) on P3 amplitude. The categorization requirements were the same in both experiments. Two patterns of results were found in experiment 1: first, when subjects had to categorize an end term within the stimulus scale the largest P3 amplitudes were elicited by this stimulus. Secondly, when all tone pitches had to be categorized separately or when the categorization of the middle tone pitch was required, P3 amplitudes were smallest for the middle tone pitch and increased in amplitude at both ends of the stimulus scale. Different patterns of results were found in experiment 2. When subjects had to categorize 1 out of 5 spoken digits the largest P3 amplitudes were elicited by this digit no matter which position it had on the stimulus scale. In addition, only negligible P3s were found in the condition in which each of the digits had to be categorized separately. It is argued (i) that spoken words yield a higher degree of distinctiveness than tone pitches and (ii) that P3 amplitude is related to the probability of response-defined task categories only to the extent that stimuli can easily be assigned to categories.

Acoustic Stimulation↗
PubMed1993

Event-related brain potential correlates of self-reported hunger and satiety.

Perception of hunger and satiety was examined by means of event-related potential (ERP) recordings. On the basis of Helson's frame-of-reference theory, it was hypothesized that hunger is perceived with reference to an actual adaptation level. ERPs were recorded to adjectives (hungry, thirsty, tired) combined with one of five adverbs (very, almost, somewhat, hardly, not). Subjects indicated whether a particular adverb-adjective combination accurately described their actual feeling of hunger, thirst, or fatigue. They were tested after they had fasted for 16 hr and another time when they were satiated. Area of P300 of the ERP was smallest for adverb-adjective combinations agreeing with the subject's actual state of hunger (i.e., adaptation level), which was almost hungry in fasting subjects and hardly hungry in satiated subjects. These P300 minima were flanked by significantly enhanced (p < 0.001) P300 areas for the immediately adjacent adverbs combined with hungry. P300 areas for adverbs combined with thirsty and tired did not depend on the subject's state of hunger. The data suggest that perception of internal states, such as hunger, refers to an adaptation level that is sensitively indicated by P300 area.

Adult↗