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Biomedical subjects

R Galambos

Publications and source records attributed to R Galambos.

At least 55 records · Page 3Linked to original sources
PubMed1977

Brain stem auditory evoked responses in children.

Evaluation of the peripheral auditory system was attempted in 81 infants and children using an electrophysiological response, the brain stem auditory evoked response (BER). These measurements, which were successfully made in all cases, were supplemented with impedance measures in some subjects. Results were compared with previous and follow-up audiograms whenever possible. The BER test proved to be a highly reliable diagnostic tool when used in assessing "difficult-to-test" patients. It also identified new patients with peripheral auditory abnormality who subsequently received confirming conventional audiological tests. The BER test results correlated well with the impedance measurements, but some rare instances of important discrepancies require further study.

Acoustic Stimulation↗
PubMed1976

Selective attention and the auditory vertex potential. I. Effects of stimulus delivery rate.

In a selective attention task, twelve subjects received random sequences of 800 and 1500 c/sec tone pips in their right and left ears, respectively. They were instructed to attend to one channel (ear) of tones, to ignore the other, and to press a button whenever occasional "targets", tones of a slightly higher pitch, were detected in the attended ear. In separate experimental conditions the randomized interstimulus intervals (ISIs) were "short" (averaging 350 msec), "medium" (960 mes) and "long" (1920 msec). The N1 component of the auditory evoked potential (latency 80--130 msec) was found to be enlarged to all stimuli in an attended channel (both targets and non-targets) but only in the short ISI condition. Thus, a high "information load" appears to be a prerequisite for producing channel-selective enhancement of the N1 wave; this high load condition was also associated with the most accurate target detectability scores (d'). The pattern of attention-related effects on N1 was dissociated from the pattern displayed by the subsequent P3 wave (300--450 msec), substantiating the view that the two waves are related to different modes of selective attention.

Adult↗
PubMed1976

Selective attention and the auditory vertex potential. Effects of signal intensity and masking noise.

A randomized sequence of tone burst was delivered to subjects at short inter-stimulus intervals (mean ISI of 333 msec), with the tones originating from one to three spatially and frequency-specific channels. The subject's task was to count the tones in one of the three channels at a time, ignoring the other two, and press a button after each tenth tone. In different conditions, tones were given at high (60 dB SL) and low (20 dB SL) intensities and with or without a background white noise to mask the tones. The N1 component of the auditory vertex potential was found to be larger in response to attended-channel tones than in relation to unattended tones. This selective enhancement of N1 was minimal for loud tones presented without noise and increased markedly for the lower tone intensity and in noise-added conditions. The selectivity of attention was measured physiologically in this multichannel listening task was thus greater when tones were faint and/or different to detect.

Adult↗
PubMed1975

Stimulus novelty, task relevance and the visual evoked potential in man.

Visual evoked potentials (VEPs) were recorded from normal adult subjects performing in a visual discrimination task. Subjects counted the number of presentations of the numeral 4 which was interposed rarely and randomly within a sequence of tachistoscopically flashed background stimuli (numeral 2s). Intrusive, task-irrelevant (not counted) stimuli were also interspersed rarely and randomly in the sequence of 2s; these stimuli were of two types: simples, which were easily recognizable (e.g., geometric figures), and novels, which were completely unrecognizable (i.e., complex, colorful patterns). It was found that the simples and the counted 4s evoked posteriorly distributed P3 waves (latency 380-430 msec) while the irrelevant novels evoked large, frontally distributed P3 waves (latency 360-380 msec). These large, frontal P3 waves to novels were also found to be preceded by large N2 waves (latency 278 msec). These findings indicate that "the P3" wave is not a unitary phenomenon but should be considered in terms of a family of waves, differing in their brain generators and in their psychological correlates. These late positive components are discussed in terms of task-relevance, recognition and Pavlov's "what is it" response.

Attention↗
PubMed1975

On hemispheric differences in evoked potentials to speech stimuli.

Eight subjects listened to lists of speech sounds (pa or ba) or pure tones (250 or 600 c/sec). Within each list one of the sounds (the "frequent") occurred more often than the other (the "target") in a ratio of approximately 4:1. Subjects were required to count the targets in each list; concurrently, evoked responses to both targets and frequents were being separately averaged from electrodes at vertex at symmetrical left and right parietal locations. The evoked responses show the expected sequence of deflections at all three electrode sites, including large P3 waves (about 350 msec latency) to the target stimuli. However, the left and right hemispheric responses to speech or tones, either frequent or target, were strikingly similar, both to the eye and by statistical tests intended to reveal differences between them.

Auditory Perception↗
PubMed1975

Brain stem auditory-evoked responses in premature infants.

Brain stem auditory-evoked responses were recorded in 24 infants ranging in age from six-weeks premature to term. At a given age, the latency of the response increased with decreasing stimulus intensity. Further, as age increased, there was a systematic decrease in latency of the response at each sound intensity level. The response was shown not to be fatigue or sleep stage. It may, therefore, be of use for evaluating auditory function in high-risk newborn infants.

Acoustic Stimulation↗
PubMed1975

Cochlear microphonics generated by microwave pulses.

Oscillations at 50 kHz have been recorded from the round window of guinea pigs during irradiation by 918-MHz pulsed microwaves. The oscillations promptly follow the stimulas, outlast it by about 200 musec and measure to 50 muV in amplitude. They precede the auditory nerve's response and disappear with death. They are interpreted to be a cochlear microphonic and hence to demonstrate that the microwave auditory effect, in the guinea pig at least, is accompanied by a mechanical disturbance of the hari cells of the cochlea.

Animals↗
PubMed1971

Human auditory attention: a central or peripheral process?

The click-evoked electrical responses of the human cochlear nerve were recorded from the external ear canal concurrently with the cortical evoked potentials from the scalp. Paying attention to the clicks during a discrimination task resulted in a highly significant enhancement of the cortical response but no change in the cochlear nerve response. Hence no evidence was obtained for the operation of a peripheral gating mechanism during attention in man.

Action Potentials↗