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Biomedical subjects

A J Kellett

Publications and source records attributed to A J Kellett.

5 recordsLinked to original sources
PubMed1990

Human evoked potentials to shifts in the lateralization of a noise.

A continuous noise was generated by running a sequence of random numbers through a digital-analog converter and connecting the output through an amplifier and filter to an earphone. Two channels were programmed to generate identical noise stimuli with one channel delayed relative to the other. When these stimuli were presented through earphones, the subject lateralized the noise to the side receiving the leading stimulus. Changes in the relative timing of the two stimuli caused the noise to shift its lateralization. Since these shifts occurred without any detectable change in the ongoing monaural noise, any potentials they evoked were specifically related to binaural interaction. The response recorded from the vertex contained a positive-negative-positive complex with peak latencies of 75, 136 and 220 ms. This response was similar to that evoked by the onset of a monaural stimulus although it was slightly smaller and significantly later. Despite several attempts, we were unable to record any definite earlier evoked potentials.

Adolescent↗
PubMed1987

Potentials evoked by the sinusoidal modulation of the amplitude or frequency of a tone.

Steady state responses to the sinusoidal modulation of the amplitude or frequency of a tone were recorded from the human scalp. For both amplitude modulation (AM) and frequency modulation (FM), the responses were most consistent at modulation frequencies between 30 and 50 Hz. However, reliable responses could also be recorded at lower frequencies, particularly at 2-5 Hz for AM and at 3-7 Hz for FM. With increasing modulation depth at 40 Hz, both the AM and FM response increased in amplitude, but the AM response tended to saturate at large modulation depths. Neither response showed any significant change in phase with changes in modulation depth. Both responses increased in amplitude and decreased in phase delay with increasing intensity of the carrier tone, the FM response showing some saturation of amplitude at high intensities. Both responses could be recorded at modulation depths close to the subjective threshold for detecting the modulation and at intensities close to the subjective threshold for hearing the stimulus. The responses were variable but did not consistently adapt over periods of 10 min. The 40-Hz AM and FM responses appear to originate in the same generator, this generator being activated by separate auditory systems that detect changes in either amplitude or frequency.

Acoustic Stimulation↗
PubMedDate not supplied

Human auditory evoked potentials recorded using maximum length sequences.

A maximum length sequence (MLS) is a specially constructed pseudorandom binary sequence that can be used to control the presentation of sensory stimuli. The evoked potentials to such a sequence of stimuli can be analyzed to give the response to one stimulus in the sequence. This procedure allows auditory evoked potentials to be recorded at stimulus rates that would cause a confusing overlap of responses with regular averaging. The MLS technique can be used with auditory evoked potentials at all latencies although it is most effective for the brain-stem and middle-latency responses. By demonstrating different refractory periods for different parts of the response, the technique may help delineate the component structure of the evoked potential. As well, an MLS analysis can disentangle the auditory brain-stem response from overlapping middle-latency responses during evoked potential audiometry.

Adolescent↗
PubMedDate not supplied

On trial: nursing.

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Family Planning Services↗