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Biomedical subjects

D F Jackson

Publications and source records attributed to D F Jackson.

At least 19 recordsLinked to original sources
PubMed1993

Contralateral suppression of non-linear click-evoked otoacoustic emissions.

Click-evoked otoacoustic emissions from nominal 80 dB pSP (peak sound pressure) 80-microseconds pulses presented at 50 pulses per second were collected from the right ears of eleven normal hearing subjects using an ILO88 Otodynamic Analyzer in the non-linear mode. Clicks, pure tones, and narrow bands of noise were then presented to their left ears through insert earphones. The 80-microseconds contralateral clicks ranged in intensity from 80 dB pSP in 5 dB steps down to 60 dB pSP but data on only 10 of the subjects were collected successfully. The pure tones and narrow bands of noise centered at 250, 500, 1000, 2000, and 4000 Hz were also presented through insert phones at 20, 40, 60 and 80 dB HL (Hearing Level) to all 11 subjects. The mean overall 'echo amplitude' without contralateral stimuli was 11 dB SPL and underwent more than 3 dB of overall suppression in response to the noises which were the most effective of the contralateral suppressors. When we analyzed the echo suppression to noise in 2-ms segments, we found consistent contralateral suppression of 3-4 dB concentrated in the time zones after 8 ms. Time shifts of more than 200 microseconds between the control and experimental traces were also observed in the same zones. The clicks were the next most effective suppressors, but showed their amplitude and time effects in somewhat earlier time zones. The tones were the least effective suppressors suggesting that efferent effects we measured in the human system are not strongly tonotopic. Because 'non-linear' mode high intensity clicks were deliberately selected as stimuli to evoke the TEOAE's, the emissions and their suppression can represent neither the 'true' TEOAE nor all of the efferent system's suppression abilities.

Acoustic Stimulation↗
PubMed1993

Does type I afferent neuron dysfunction reveal itself through lack of efferent suppression?

We present here two patients and three control subjects to demonstrate the clinical utility of studying evoked otoacoustic emissions and their contralateral suppression, as an aid to the delineation of afferent neuron dysfunction and possible lack of efferent suppression. The key patients here who fail to show contralateral suppression of their very robust otoacoustic emissions, concomitantly show paradoxically absent auditory brainstem responses (ABRs) and absence of middle ear muscle reflexes despite normal audiograms in the 2 kHz region and normal tympanograms. One of these patients has nearly normal pure tone sensitivity up to 3 kHz. The other has normal sensitivity in the 2 kHz region, but poor sensitivity on either side of that frequency. In addition, the two patients of interest show absent masking level differences and inordinately poor speech discrimination. Three 'foils' are presented: one patient with poor hearing on either side of 2 kHz, one with Bell's Palsy, and the third with bilateral temporal lobe disease. These patients show respectively that (1) isolated normal hearing at 2 kHz, (2) absence of middle ear muscle reflexes and (3) conscious cortical awareness of sound do not contribute directly to this intriguing clinical state. We propose that these patients with absent ABRs suffer from an auditory nervous system dysfunction which disrupts access to the efferent system. This condition also disables whatever systems contribute to the neural synchrony inherent in recording compound far-field action potentials such as the ABR. There are a number of hypotheses to be considered here. One suggests that the key patients are deficient in synchronous activation of Type I afferent fibers to the degree that they cannot activate efferent feedback, or they may be able to use only so-called Type II afferent neurons to support their normal zones of pure tone sensitivity. A less likely consideration focuses on the notion that discharge of primary neurons might be in some way synchronized by an efferent system which in these patients is the primary source of deficit.

Acoustic Impedance Tests↗
PubMed1991

Discrimination of formant transition onset frequency: psychoacoustic cues at short, moderate, and long durations.

Two experiments determined the just noticeable difference (jnd) in onset frequency for speech formant transitions followed by a 1800-Hz steady state. Influences of transition duration (30, 45, 60, and 120 ms), transition-onset region (above or below 1800 Hz), and the rate of transition were examined. An overall improvement in discrimination with duration was observed suggesting better frequency resolution and, consequently, better use of pitch/timbre cues with longer transitions. In addition, falling transitions (with onsets above 1800 Hz) were better discriminated than rising, and changing onset to produce increments in transition rate-of-change in frequency yielded smaller jnd's than changing onset to produce decrements. The shortest transitions displayed additional rate-related effects. This last observation may be due to differences in the degree of dispersion of activity in the cochlea when high-rate transitions are effectively treated as non-time-varying, wideband events. The other results may reflect mechanisms that extract the temporal envelopes of signals: Envelope slope and magnitude differences are proposed to provide discriminative cues that supplement or supplant weaker spectrally based pitch/timbre cues for transitions in the short-to-moderate duration range. It is speculated that these cues may also support some speech perceptual decisions.

Attention↗
PubMed1987

Effects of radioactive decay and their implications on in vivo metabolic imaging.

In the context of medical radionuclide imaging, possible consequences of molecular disruption that is due to radioactive decay and of the positron range are discussed. Radioactive decay may cause extensive disruption to the labeled molecule particularly if the transformation involves the creation of an inner shell vacancy. The movement of a positron away from the site of emission implies that the positron will annihilate in a region not disrupted by the decay. Neglect of the photon angular correlation disregards information on the physical and chemical state of the sample.

Humans↗
PubMed1986

Tissue analysis by dual-energy computed tomography.

A straightforward method of tissue analysis from dual-energy computed tomography (CT) is presented which does not rely on previous inaccurate or incorrect formulations of the X-ray attenuation coefficient. The attenuation coefficients of tissue and bone were represented by a mixture of two reference materials. For convenience, water and calcium chloride were chosen. After careful calibration of the CT scanner, a dual-energy CT scan yields the water and calcium chloride in units of kg/kg multiplied by the specific gravity of the tissue. For an error of +/- 2 HU on dual-energy scans at 140 kVp and 87 kVp on an EMI CT5005 general-purpose scanner, the error on the calcium chloride coefficients is +/- 0.004 kg/kg. Fat concentrations greater than 25% by weight may be detected when the coefficients are averaged over at least 200 pixels. Bone mineral content could be measured with a precision of 0.01 (in units of kg/kg multiplied by specific gravity) for averaging regions of 24 pixels. Iodine concentrations in tissue can be deduced if water and iodine are chosen as the reference materials. Clinical examples are presented to illustrate the technique for scans of both the head and the abdomen.

Abdominal Neoplasms↗
PubMed1981

Small-angle multiple scattering and spatial resolution in charged particle tomography.

The formulae for the RMS scattering angle given by small-angle multiple-scattering theory are discussed and a correction to the standard Rossi formula is derived. Values of the correction factor are calculated for protons, alpha-particles and heavy ions; these results show that the correction is important for protons and alpha-particles but negligible for heavy ions with mass number 12-40. The values of the RMS scattering angle and the RMS lateral displacement are calculated for a proton beam passing through water. For protons the correction for energy loss in thick targets is even more important.

Alpha Particles↗