PubMed Health⌕ Search

Biomedical subjects

H Hagendorf

Publications and source records attributed to H Hagendorf.

6 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↗
PubMed1996

Coordination in visual working memory.

Coordination of mental procedures is considered in terms of control processes (Baddeley, 1989) in visual working memory and appears to be a separable aspect of the demand imposed by cascaded serial processes (Carlson & Lundy, 1992). The main task required subjects to indicate whether symbolically suggested rotations and reflections correctly describe the difference between matrix patterns of filled-in squares within a 3 x 3 grid or between line drawings. Experiments were carried out to show that coordination is a separable component in this transformation task. A marker for coordination is the difference between the time taken to execute two transformations as a whole and the sum of the component transformations in isolation. The separate coordination demand was found in an experiment with matrix patterns mentioned, in an experiment with letter-like line drawings, and also in an experiment that forced subjects to maintain whole-pattern representations. A last experiment checked whether coordination is carried out by an autonomous control unit. There was a self-paced control of serial presentation of transformation symbols instead of a simultaneous presentation of those symbols. This additional external triggering resulted in a substantial decrease in the demand for coordination. Coordination of mental procedures and temporary representations is a fundamental constraint on the use of working-memory processes.

Adult↗
PubMed1995

[Coordination processes in visual working memory].

Starting with a discussion on the coordination problem from different points of view within cognition the question is raised whether there is a dissociation of coordination demand of a task and the mental load for executing mental procedures. Three investigations are carried out with the paradigm of sequential mental transformations of patterns. Results of the first experiment show that coordination really requires additional mental effort beside the time necessary for mental transformation. In a further study the transfer of a coordination mechanism is proved. The influence of segmented information presentation demonstrates that amount of coordination is related to the stability and clarity of mental representations. Plans for further experiments are presented. The results are related to the current literature on working memory research.

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↗