Biomedical subjects

W Teder

Publications and source records attributed to W Teder.

9 recordsLinked to original sources

PubMed1997

Magnetoencephalographic recording of steady-state visual evoked cortical activity.

Steady-state visual evoked magnetic fields (SSVEFs) were recorded in response to a flickering light source using a 37-channel magnetometer. The SSVEF had a sinusoidal waveform having the same fundamental frequency as the driving stimulus, which was either 6.0 Hz, 11.9 Hz, or 15.2 Hz. SSVEF topographies at each frequency had a dipoloar form over the posterior head that could well-modelled by single equivalent current dipoles. The best-fit dipoles were localized in posterior occipital cortex for the SSVEFs to 6.0 and 11.9 Hz stimuli and in more anterior and ventromedial occipital cortex for the 15.2 Hz SSVEP.

Adult↗

PubMed1994

Event-related potentials demonstrate a narrow focus of auditory spatial attention.

The distribution of spatial attention across neighbouring sound sources was investigated by assessing event-related potentials (ERPs) to tone probes embedded in natural speech during a selective-attention task. Concurrent speech messages were delivered from the middle positions of two groups of three sound sources in free-field in front of the subject, one to the left and the other to the right of the midline. In each group, the two extreme neighbour loudspeakers were positioned very closely to the middle ones. Brief tone pips were delivered from all locations in a random order. ERPs elicited by the tone probes used to probe the extent of spatial attention showed its narrow focus, one comparable to that suggested by behavioural studies.

Acoustic Stimulation↗

PubMed1994

Strongly focused attention and auditory event-related potentials.

Effects of selective attention on the auditory event-related potential were studied by delivering two tones in a rapid, randomized sequence. One of the tones was designated as relevant and the other as irrelevant, the subject's task being to discriminate occasional softer tones within the relevant tones. Relevant and irrelevant tones differed from each other either in location (left vs. right ear) or pitch (300 vs. 6000 Hz). In both conditions, relevant tones elicited a larger N1 deflection (peak latency about 120 ms) than did irrelevant tones. In contrast to the exogenous N1 elicited by unattended tones, the scalp distribution of this attentional "N1 effect" did not depend on the stimulated ear and, further, its amplitude was not affected by the frequency of attended tones. These results suggest that the present attention effect was caused, at least mainly, by an endogenous processing negativity rather than by an enhancement of exogenous N1 components.

Adult↗

PubMed1993

Selection of speech messages in free-field listening.

Event-related brain potentials (ERPs) elicited by initial consonants of words in a spoken message were recorded from 10 human subjects. In an ecologically valid free-field situation, brain responses to speech were recorded for the first time without using artificial probe stimuli as ERP trigger signals. In an analogy to a 'Cocktail-Party' situation in its most elementary form, two concurrent stories were delivered via separate left and right loudspeakers. The subject's task was to selectively attend to a designated message while ignoring the other. Results show a very early attention effect for a speech message commencing at about 40 ms from stimulus onset. This early effect appears to be based on tonic facilitation of the attended message and contextual cues.

Cues↗

PubMed1993

Memory prerequisites of mismatch negativity in the auditory event-related potential (ERP).

The mismatch negativity (MMN) is a component of the auditory event-related brain potential that occurs in response to infrequent changes in the physical properties of homogeneous series of sounds, even when subjects are instructed to ignore the auditory channel of stimulation. It has been proposed (e.g., Näätänen, 1990) that the MMN is generated by an automatic process in which a difference between the deviant sound and the previous, standard sound is detected by the brain. However, it is unclear how the form of memory involved is related to the rest of the memory system. The present study indicates that, for an MMN to be elicited in response to a change in tone frequency, the representation of the standard tone must be both (a) well-established as a standard in memory, and (b) in a currently active state. The relation between physiological and psychological aspects of memory representation is discussed.

Acoustic Stimulation↗

PubMed1993

Interstimulus interval and the selective-attention effect on auditory ERPs: "N1 enhancement" versus processing negativity.

The attention effect on the auditory event-related potential (ERP) in dichotic conditions was studied as a function of the interstimulus interval (ISI). Subjects attended to stimuli delivered to a designated ear and responded to infrequent pitch deviants in this input. The mean ISI was either 80, 160, 480, or 800 ms. Negative difference waves (Nds) were computed by subtracting ERPs to unattended standards from ERPs to the same stimuli when attended. The exogenous N1, as estimated from unattended standard ERPs, was larger contralaterally to the stimulus and inverted in polarity at mastoids. With decreasing ISIs, N1 diminished in amplitude much faster than did the Nd. In addition, N1 latency remained stable, whereas Nd peaked markedly earlier with shorter ISIs, almost perfectly coinciding with the exogenous N1. However, this temporal coincidence found in grand averages proved to be illusory in single subjects. The early Nd showed no contralateral asymmetry at its peak, but asymmetry was apparent during the ascending slope. These lateral asymmetries resembled those of the exogenous N1 but occurred later. The early Nd peak was, at least mainly, caused by an endogenous attention effect, the processing negativity (PN), even with very short ISIs, but an effect on the exogenous N1 could not be excluded.

Adult↗

PubMed1992

Auditory attention and selective input modulation: a topographical ERP study.

Event-related potentials (ERPs) were recorded in subjects receiving tones (left ear 300 Hz, right ear 6000 Hz) at a rapid rate and trying to detect occasional higher-pitched stimuli in a designated ear. ERPs to attended stimuli showed enhanced negative amplitudes whose topographical distribution differed from that of the exogeneous N1 component. Moreover, the latter was considerably larger for low than high tones, whereas the attention effect had similar amplitudes for the two tones. Consequently, the attention effect, even when perfectly coinciding in time with N1, does not seem to be caused by modulation of the exogeneous N1 but rather by a separate process activated by attention. This suggests that attention does not modulate initial stimulus representations in audition.

Acoustic Stimulation↗

PubMed1991

Attention effects on the auditory event-related potential.

Studies on selective-attention effects on the auditory event-related brain potential (ERP) are reviewed. Brainstem components of the ERP have not been shown to be sensitive to attention. On the other hand, attention effects in the middle-latency range (12-50 ms from stimulus onset) appear to occur under some conditions but it is not clear whether these effects are exogenous or endogenous. The predominant attention effect on the auditory ERP is the processing negativity, a slow endogenous negativity which often commences well before the exogenous (supratemporal) N1 component peaks (at about 100 ms post-stimulus), therefore giving the impression that this exogenous component is attention-sensitive. It is not yet settled, however, whether even these exogenous processes under some conditions might be modulated by selective attention.

Acoustic Stimulation↗

PubMedDate not supplied

Reliability of life event assessments: test-retest reliability and fall-off effects of the Munich Interview for the Assessment of Life Events and Conditions.

This paper presents the findings of two independent studies which examined the test-retest reliability and the fall-off effects of the Munich Life Event List (MEL). The MEL is a three-step interview procedure for assessing life incidents which focuses on recognition processes rather than free recall. In a reliability study, test-retest coefficients of the MEL, based on a sample of 42 subjects, were quite stable over a 6-week interval. Stability for severe incidents appeared to be higher than for the less severe ones. In the fall-off study, a total rate of 30% fall-off was noted for all incidents reported retrospectively over an 8-year period. A more detailed analysis revealed average monthly fall-off effects of 0.36%. The size of fall-off effects was higher for non-severe and positive incidents than for severe incidents. This was particularly evident for the symptomatic groups. Non-symptomatic males reported a higher overall number of life incidents than females. This was partly due to more frequent reporting of severe incidents. The findings of the fall-off study do not support the common belief that the reliability of life incident report is much worse when the assessment period is extended over a period of several years as compared to the traditional 6-month period.

Adult↗