PubMed Health⌕ Search

Biomedical subjects

K Grune

Publications and source records attributed to K Grune.

8 recordsLinked to original sources
PubMed2000

Updating of working memory in a running memory task: an event-related potential study.

The aim of the study was to identify central executive activity in the event-related potential (ERP) in the time and space domain. Lists of three to eight consonants were presented sequentially. After each list the ordered recall of the three most recent items was required. In this running memory task the updating of working memory contents from the fourth letter on may be understood as a control process. ERPs elicited from each consonant presented in the lists were subtracted from those of a control condition that was also applied to the participants. The difference waveforms showed fronto-central distributed positivities, probably indicating the activity of a postulated central executive. This finding confirms those of neuroimaging studies that localize executive activity to prefrontal brain areas.

Adult↗
PubMed1997

[Effect of preload of working memory on components of evoked potentials during encoding of sequentially presented letter sequences].

In recent experiments with a pseudo-random sequence of 7 consonants to recall after trial (stimulus onset asynchrony 1000 ms) a reverse relationship between P300 amplitude of the event-related potential (ERP) and letter presentation position was shown (Grune et al., 1996). It was assumed that this relationship reflects competition between encoding and retention processes in this time regime. In order to find evidence for the resource competition hypothesis in working memory a 4 x 4 grid containing 4 digits preceded a sequence of 6 consonants. In the first block subjects were instructed to ignore the grid, in two remaining blocks they were asked to remember the digits or their position in the grid and to recognize them after the letter recall. In the ignore condition the expected effect of P300 decrease with letter position was found, especially at posterior electrode sites. When subjects had to process the preceding digit grid there was no position effect of P300 caused by small P300 amplitudes in the ERPs that were elicited by the first letters of the sequence. This effect was not specific to the modality of the interfering with the letter task information from the digit grid. We conclude that the grid information occupies working memory resources that are not available for the event-related processing of consonants to recall.

Adult↗
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↗
PubMedDate not supplied

Information processing in working memory and event-related brain potentials.

Information processing in working memory was investigated in a paradigm with a pseudo-random sequence of visually presented consonants. The subjects' task was to memorize seven sequentially presented letters per trial and to recall the sequence (MEMORY task). Even-related potentials (ERPs) were selectively averaged for each of the seven positions of consonant presentation within a trial. The later a consonant was presented within a trial the smaller the P300 amplitude elicited by the consonant. The number of recall errors increased, however, from first to last presentation position. In a control task identical to the MEMORY condition consonant were presented. To limit the working memory load to one element, subjects had to count the number of letters within trials showing a specific physical criteria. P300 amplitude did not depend on presentation position. P300 was shown to covary with the amount of processing resources available for a task. We assume that increasing working memory load consumes processing resources that are not available for the processing of the incoming stimuli presented later in the trial.

Adult↗