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Biomedical subjects

D McFadden

Publications and source records attributed to D McFadden.

At least 19 recordsLinked to original sources
PubMed1992

Evidence that adaptation of suppression cannot account for auditory enhancement or enhanced forward masking.

Delaying the onset of a signal relative to the onset of a simultaneous notched masker often improves the ability of listeners to 'hear out' the signal at both threshold and suprathreshold levels. Viemeister & Bacon (J. acoust. Soc. Am., 71, 1502-1507 (1982)) suggested that such auditory enhancement effects could be accounted for if the suppression produced by the masker on the signal frequency adapted, thereby releasing the signal from suppression. In support of their hypothesis, Viemeister & Bacon reported that a masker preceded by an enhancer having no component at the signal frequency produced more forward masking than did the masker by itself. Here evidence is provided from five new experiments showing that adaptation of psychophysical two-tone suppression is inadequate to account either for auditory enhancement effects or for the enhanced forward masking demonstrated by Viemeister & Bacon.

Acoustic Stimulation↗
PubMed1992

Temporal decline of masking and comodulation masking release.

Masking sounds can be continuously present, gated simultaneously with the signal, or gated somewhat prior to the signal. This continuum of relative onset times was explored using waveforms of the sort commonly employed in studies of comodulation masking release (CMR). There was a 50-Hz masker band centered on the 1250-Hz tonal signal, and four 50-Hz flanker bands centered at 850, 1050, 1450, and 1650 Hz. In some conditions, all four flanker bands had the same temporal envelope, and the masker band either had that same envelope (correlated presentations) or a different envelope (uncorrelated presentations). In other conditions, all five bands had different temporal envelopes (all-uncorrelated presentations). The masker band and/or the four flanker bands were either gated nearly simultaneously with the signal (burst conditions) or were gated prior to the signal by a duration that was systematically varied (fringed conditions). The eight listeners could be partitioned into three groups on the basis of their response to these fringing manipulations. Two listeners (the large fringers) showed a gradual improvement in detectability with increasing fringe duration (called a temporal decline of masking), while three others (the small fringers) showed little improvement in detectability. For the remaining three subjects, there was evidence of a "learning" effect that changed them from large fringers to small fringers over a 10-week period of listening. When present, the temporal decline of masking was greater for the correlated than for the uncorrelated comodulation condition; as a consequence, the difference in detectability between them (the comodulation masking release or CMR) increased with fringe duration. By fringing the masker and flanker bands separately and in combination, it was revealed that the temporal declines of masking were primarily attributable to the fringing of the flanker bands. In contrast, large CMRs required long fringes on both the masker and flanker bands. The above results were obtained with 50-ms signals, but generally similar data were obtained with a signal duration of 240 ms. The difficulties raised for experimentalists and theorists by such long-term practice effects are discussed.

Adult↗
PubMed1990

Reductions in overshoot during aspirin use.

The overshoot effect was measured before, during, and after the administration of a moderate dose of aspirin. Prior to the drug, detectability of the 6-ms, 3550-Hz signal was 5-11 dB worse when presented 2 ms after the onset of the 200-ms wideband masking noise than when presented 190 ms after masker onset. Following 4 days of aspirin use, detectability in the long-delay condition was unchanged from the predrug value, but (for four of the five subjects) detectability in the short-delay condition was improved by about 4-8 dB. Thus the overshoot effect was markedly reduced by aspirin because the drug partially counteracted the normally poor detectability for signals presented soon after masker onset. This paradoxical improvement in detectability was accompanied by an aspirin-induced loss in detectability of 5-16 dB for a 200-ms sample of that same signal presented in the quiet. Similar paradoxical effects have previously been obtained by inducing a temporary hearing loss with exposure to intense sound. It is presumed that the same basic mechanisms underlie the parallel outcomes. The so-called cochlear amplifier is discussed in this regard, and also the possibility that the known differences in those primary auditory fibers having high and low spontaneous rates may be involved. A supplementary experiment demonstrated that shifting audibility with either a wideband or a narrow-band background noise does not affect the overshoot effect in the same way as does aspirin or exposure to intense sound, further suggesting that the cochlear amplifier must be altered in order for overshoot to be diminished.

Acoustic Stimulation↗
PubMed1990

Uncertainty about the correlation among temporal envelopes in two comodulation tasks.

The threshold of a 1250-Hz tonal signal was measured in the presence of five noise bands (each 50 Hz wide, centered at 850, 1050, 1250, 1450, and 1650 Hz) under five conditions of uncertainty about the waveform type ("correlated" or "uncorrelated"), and/or the specific waveform sample to be presented. The waveform type was correlated when the temporal envelopes of all of the noise bands were the same, and was uncorrelated when the temporal envelope of the band centered on the signal differed from the common envelope of the other bands. At the low-uncertainty end of the continuum of conditions, the same waveform type was presented throughout an entire block of trials, and, in addition, the same waveform sample was presented on the two observation intervals of a single trial (but changed across trials). At the high-uncertainty end of the continuum, both the waveform type and the waveform sample were chosen at random for every observation interval. Threshold estimates obtained from trials in which both observation intervals contained the same waveform type were not affected by uncertainty about the waveform sample within a trial, nor by uncertainty about the waveform type introduced across trials. Thus the comodulation masking release, or CMR (the difference in the thresholds obtained with the uncorrelated and correlated waveforms), calculated from these types of trials was robust across all of the uncertainty conditions. However, on those trials in which one correlated interval and one uncorrelated interval were paired, threshold estimates were influenced by a bias for listeners to choose the uncorrelated interval as the signal interval, whether or not it actually contained the signal. This bias reveals the importance of recognizing the contribution of the nonsignal interval in experiments involving masker uncertainty. Parallel results were obtained using the comodulation detection difference (CDD) task. In some conditions, marked individual differences were observed.

Adolescent↗
PubMed1990

Temporal decline of masking and comodulation detection differences.

Comodulation detection differences (CDDs) were studied using flanking bands that were either gated simultaneously with the signal band (burst) or gated at varying times prior to signal onset (fringed). Used for these experiments were a signal band centered at 1250 Hz and four flanking bands centered at 450, 850, 1650, and 2050 Hz; all bands were 100 Hz wide. In different conditions, the temporal envelope of the signal band was either the same as (correlated), or different from (uncorrelated), the common envelope of the four flanking bands, or the temporal envelopes of all of the bands were different (all-uncorrelated). For 8 of the 13 listeners, signal detectability improved by as much as 25 dB as the temporal fringe of the flanking bands was increased from 5 to about 700 ms. This temporal decline of masking was similar, but not identical, for the correlated, uncorrelated, and all-uncorrelated conditions. Results of this sort are reminiscent of several related findings that have been attributed to auditory adaptation or enhancement, or to a temporally developing critical-band filter. The other 5 of the 13 listeners were generally more sensitive than the majority, and they showed little or no improvement in detectability as fringe duration was varied. Large individual differences of this sort are not uncommon in the adaptation and comodulation literatures. As signal duration was changed from 50 to 240 ms, temporal integration was less in the correlated condition than in the uncorrelated condition, thereby producing a larger CDD with the longer signal. When the fringe followed the observation interval instead of preceding it, the results were equivocal because detectability improved for the majority of subjects and worsened for the minority. In follow-up experiments, different subsets of these four flanking bands were used. When temporal gaps of varying duration were inserted into the flanking band(s) immediately prior to the observation intervals, it was found that a temporal gap as long as 355 ms was not sufficient to reset the mechanisms underlying the temporal decline of masking.

Adult↗
PubMed1989

Reductions in overshoot following intense sound exposures.

Overshoot refers to the poorer detectability of brief signals presented soon after the onset of a masking noise compared to those presented after longer delays. In the present experiment, brief tonal signals were presented 2 or 190 ms following the onset of a broadband masker that was 200 ms in duration. These two conditions of signal delay were tested before and after a series of exposures to a tone intense enough to induce temporary threshold shift (TTS). The magnitude of the overshoot was reduced after the exposure when a TTS of at least 10 dB was induced, but not when smaller amounts of TTS were induced. The reduction in overshoot was due to a decrease in the masked thresholds with the 2-ms delay; masked thresholds with the 190-ms delay were not different pre- and post-exposure. The implication is that the mechanisms responsible for the normal overshoot effect are temporarily inactivated by the same stimulus manipulations that produce a mild exposure-induced hearing loss. Thus the result is the paradox that exposure to intense sounds can produce a loss of signal detectability in certain stimulus conditions and a simultaneous improvement in detectability in other stimulus conditions.

Acoustic Stimulation↗
PubMed1986

Effect of luminally administered serotonin and substance P on jejunal handling of water and electrolytes.

This study was initiated to evaluate the effect of luminally administered serotonin (5-hydroxytryptamine) and substance P on jejunal handling of water and electrolytes. Five dogs with chronic cannulated jejunal Thiry-Vella loops were studied. The isolated jejunal segments were perfused at 2 ml/min for 2 hours with an isosmotic, isothermic perfusate containing labeled polyethylene glycol for recovery calculation. Fluxes of water and sodium, chloride, and potassium were calculated during 30 minute baseline, 60 minute study, and 30 minute recovery periods. Substance P was administered intraluminally at 25 pg/ml, whereas serotonin was perfused at 600 ng/ml. Neither hormone was absorbed into the portal circulation. Intraluminal serotonin converted absorption to secretion of water from 43 +/- 23 to -105 +/- 25 microliters/min, sodium from 7.3 +/- 3.1 to -15.7 +/- 4.1 microEq/min, chloride from 4.4 +/- 3.4 to -16.4 +/- 3 microEq/min, and potassium from 0.16 +/- 0.20 to -0.86 +/- 0.17 microEq/min. Secretion ceased on cessation of serotonin perfusion. Substance P perfusion induced secretion of chloride (3.6 +/- 1.9 to -9.2 +/- 2.9 microEq/min) but only significantly decreased absorption of water (73 +/- 13 to 13 +/- 21 microliters/min) and sodium (8.1 +/- 1.9 to 0.2 +/- 3.1 microEq/min); in contrast, there was no significant change in jejunal handling of potassium.

Animals↗
PubMed1986

Verapamil reversal of serotonin-induced jejunal secretion of water and electrolytes in awake dogs.

Intestinal handling of water and electrolytes was monitored in 5 conscious dogs with chronic 25-cm Thiry-Vella loops of proximal jejunum using a neutral isosmotic perfusate containing [14C]polyethylene glycol as a recovery marker. Under basal conditions the animals absorbed water, Na+, and Cl-, and there was minimal nonsignificant secretion of K+. Intravenous serotonin infusion (30 micrograms/kg X min) increased circulating hormone levels to 937 +/- 131 ng/ml and induced significant secretion of water (-150 +/- 52 microliter/min), Na+ (-22.8 +/- 8.4 microEq/min), Cl- (-23.5 +/- 6.0 microEq/min), and K+ (-1.79 +/- 0.34 microEq/min). Simultaneous infusion of verapamil, a calcium channel blocker, at 8.3 micrograms/kg X min, reversed the intestinal secretion to absorption of all these parameters (144 +/- 32 microliter/min, 15.1 +/- 5.1 microEq/min, 10.3 +/- 3.0 microEq/min, and 0.12 +/- 0.23 microEq/min, respectively). This was accompanied by a significant improvement in the clinical appearance of the animals, decreased visible agitation, and cessation of defecation. Cessation of verapamil infusion (leaving the serotonin infusion unopposed) resulted in prompt return to the secretory state. Serum electrolytes did not change significantly, with the exception of potassium, which fell from 5.1 +/- 0.2 to 4.1 +/- 0.1 mg/dl. In control experiments (no serotonin), verapamil had an insignificant stimulatory effect on the absorption of water, Na+, and Cl- whereas the effect on K+ was significant (-0.2 +/- 0.2 to +0.4 +/- 0.1 microEq/min; p less than 0.05). These data support the role of calcium in modulating the effects of serotonin, and they suggest a new promising technology for the management of serotonin-induced intestinal secretion such as that seen in the carcinoid syndrome.

Animals↗
PubMed1986

Substance P-induced intestinal secretion of water and electrolytes.

This study was initiated to determine if raised (carcinoid) plasma concentrations of substance P induced jejunal secretion of water and electrolytes. Five dogs had isolated and cannulated 25 cm jejunal segments perfused at 2 ml/min with a neutral, isotonic perfusate. Saline, 1.0 ml, was infused intravenously during basal and recovery periods, while substance P was administered intravenously at 75 ng/kg/min (55 pmol/kg/min) during the four 15 minute experimental periods. Infusion increased plasma SP concentrations from basal (5.8 +/- 1.3 pg/ml) to a mean plateau level of 121.2 +/- 25.2 pg/ml (mean +/- SEM). During SP infusion, intestinal secretion of water, Na+, and Cl- were documented (H2O basal +102 +/- 60 to SP -275 +/- 60; microliter/min; Na+ basal +19.8 +/- 7.2 to SP -23.2 +/- 7.5 microEq/min; Cl- basal 21.7 +/- 7.5 to SP -16.5 +/- 5.6 microEq/min). Under basal conditions, there was minimal secretion of potassium (-0.264 +/- 0.282 microEq/min); during SP infusion, K+ flux was altered to significant secretion (-1.784 +/- 0.271 microEq/min). Serum concentrations of Na and Cl were unchanged during SP infusion, but serum potassium concentrations fell from 4.64 +/- 0.12 to 3.85 +/- 0.40 mEq/l. The data demonstrate that substance P at levels noted in the carcinoid syndrome induces significant jejunal secretion of water and electrolytes in the dog.

Animals↗
PubMed1985

Verapamil inhibition of the intestinal effects of substance P.

The undecapeptide substance P (SP) is contained in enterochromaffin cells and circulates in high concentrations in patients with carcinoid syndrome. We have previously reported that elevated SP levels, simulating those reported in patients with carcinoid syndrome, induce profound changes in intestinal water and electrolyte secretion, motility, and blood flow in a canine model. The purpose of this study was to attempt to block the effects of circulating carcinoid levels of SP on intestinal secretion and motility with the calcium channel blocker verapamil. In five dogs a chronic proximal jejunal Thiry-Vella loop was constructed, and after a 2-week recovery the loops were perfused with an isotonic test solution containing 14C-polyethylene glycol as a volume marker. Motor activity was measured by changes in intraluminal pressure and a motility index was calculated with computer-assisted planimetry and expressed as square millimeters per 5 minutes. After a 30-minute baseline period, SP was infused at 50 ng/kg/min for 90 minutes. SP circulating levels rose from a baseline of 6.2 +/- 1.3 pg/ml to a peak of 93.3 +/- 3.1 pg/ml during this infusion. Thirty minutes after the start of this SP infusion, a simultaneous infusion of verapamil (5.0 micrograms/kg/min) was begun at a separate site. During SP infusion there was a significant secretory response of water (-48 +/- 12 microliters/min), Na+ (-7.7 +/- 2.5 microEq/min), Cl- (-8.8 +/- 2.7 microEq/min) and K+ (-0.57 +/- 0.14 microEq/min), and hypermotility (motility index: 1479 +/- 138 mm2/5 min). When verapamil was added a reversal of secretion to net absorption was observed (water: + 116.9 +/- 15.6 microliter/min; Na+: + 13.8 +/- 2.1 microEq/min; Cl-: + 5.5 +/- 2 microEq/min; K+: + 0.38 +/- 0.9 microEq/min) (p less than 0.05). In addition, there was a reduction in motility (motility index: 853 +/- 92 mm2/5 min; p less than 0.05). These results confirm that SP has profound effects on both intestinal motility and secretion and that calcium channel blockade reduces these effects significantly.

Animals↗
PubMed1978

Binaural detection at high frequencies with time-delayed waveforms.

Recent research has demonstrated that the binaural system can utilize ongoing interaural time differences for lateralization at high frequencies as well as at low frequencies. The requirement is that the signal be complex so that the time difference appears as a delay in the envelope of the waveform at one ear. Reported here are several masking experiments that examine detection performance with time-delayed signals or maskers. In the first experiment, the signal was a 50-Hz band of noise centered at 4000 Hz that was time delayed by different amounts on different blocks of trials; the masker was similar band of noise, presented diotically. Large masking-level differences (MLDs) were obtained for some values of time delay, but the MLDs did not increase monotonically within time delay as they should were envelope time delay the basis for detection performance. Subsequent experiments in which the masker was time delayed and the signal was a diotic, high-frequency tone, revealed that detectability follows the autocorrelation function, and that MLDs as large as 24 dB can be obtained at 4000 Hz at time delays corresponding to negative values in the autocorrelation function. Examination of the signal-plus masker waveforms in these conditions reveals that ongoing interaural differences in level and cycle-by-cycle time exist in those conditions that yield MLDs. Since the time differences are small by usual standards, the basis for detection performance in these conditions appears to be the ongoing interaural level differences. In a final experiment, lateralization performance was measured for a time-delayed, complex waveform in the presence of maskers of various intensities. The results show that subjects are able to extract information about the time delay in the envelope even when the signal is added to a masker of equal intensity or greater. Thus, at the small signal-to-noise ratios used in our detection experiments, extraction of envelope time information was impossible, but also unnecessary, for detection was accomplished on the basis of another cue--most likely the ongoing interaural level differences.

Auditory Perception↗
PubMed1975

Binaural beats at high frequencies.

Binaural beats have long been believed to be audible only at low frequencies, but an interaction reminiscent of a binaural beat can sometimes be heard when different two-tone complexes of high frequency are presented to the two ears. The primary requirement is that the frequency separation in the complex at one ear be slightly different from that in the other--that is, that there be a small interaural difference in the envelope periodicities. This finding is in accord with other recent demonstrations that the auditory system is not deaf to interaural time differences at high frequencies.

Auditory Pathways↗