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D McFadden

Publications and source records attributed to D McFadden.

At least 55 records · Page 3Linked to original sources
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

Spectral differences in the ability of temporal gaps to reset the mechanisms underlying overshoot.

When very brief tonal signals are presented immediately after the onset of a gated noise masker, detectability can be 10-20 dB worse than when the signal is delayed by several hundred milliseconds, an effect known as the overshoot. It has long been known that, when an "onset" is created in an otherwise continuous, broadband masker by briefly turning it off and on again, the detectability of a brief signal presented soon after this temporal gap will decline gradually as the gap is increased from a few milliseconds to a few hundred milliseconds. In other words, the auditory system recovers to its quiescent, resting state following an adequate silent interval. Here, the broadband maskers consisted of three adjacent spectral bands--one centered on the frequency of the tonal signal, one low passed below the lower edge of the center band, and one high passed above the upper edge of the center band. The signal was a 2500-Hz tone having a total duration of 6 ms. In different blocks of trials, either all three bands, only the center band, or only the two flanking bands were temporally gapped by a duration ranging from 10-300 ms. When the center band was about 750 Hz wide (about 2.5 critical bandwidths), this differential gapping process resulted in typical recovery functions when all three bands (the entire spectrum) or when just the two flanking bands were gapped. However, when only the center band was gapped, there was no evident recovery--rather, detectability remained near the signal level required with a continuous masker, even for a gap duration of 300 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
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↗
PubMed1989

How to gain maximum returns through cash management.

Cash concentration and controlled disbursement are cash management techniques that can enable healthcare organizations, particularly those with multiple corporations, to improve the control of cash flows, reduce excess cash balances, and increase interest earnings. Cash concentration involves transferring all cash balances into one account, while controlled disbursement involves the early notification of check clearings, enabling cash managers to fully invest available bank account balances daily.

Accounting↗
PubMed1988

Failure of a missing-fundamental complex to interact with masked and unmasked pure tones at its fundamental frequency.

Of interest here are the mechanisms underlying the extraction of temporal periodicities from complex acoustic stimuli. Two extreme versions of the underlying mechanisms are examined for possible psychophysical consequences, and experiments of two sorts are reported. In one, the detectability of a 200-Hz tone was measured in the presence, and the absence, of a tonal complex that gives rise to the experience of a missing fundamental having a pitch of 200 Hz in an attempt to see if the missing-fundamental waveform contributes to the masking of the tonal signal. We call this periodicity masking, but were unable to measure any, implying that if periodicity information was being used both to detect the signal and to perceive the missing fundamental, those two streams of afferent information are kept separate by the auditory nervous system, at least initially. In the second set of experiments, an "informational-masking" paradigm was used to introduce high uncertainty about the frequency of the tonal signal, and both detection and frequency discrimination were measured in the presence and absence of a missing-fundamental complex. This time the question was whether the periodicity information in the complex would produce a reduction in the frequency uncertainty about the signal and, thereby, improve performance. We call this possible effect periodicity cueing, but were unable to find evidence for its existence either. The failure to find either periodicity masking or periodicity cueing is discussed in regard to possible organizations of the auditory system, and in regard to the "periodicity-rate gap" seen in primary auditory fibers.

Cues↗
PubMed1988

Absence of overshoot in a dichotic masking condition.

Brief tonal signals presented soon after the onset of a masking noise are known to be less detectable than signals delayed by several hundred milliseconds. This difference in detectability is known as the "overshoot." Signals of two sorts were studied here--either interaurally in phase (S o) or interaurally out of phase by 180 degrees (S pi). When S omicron signals of 750 Hz and about 14 ms in duration were presented 4 ms after the onset of a diotic, broadband masking noise (N o), detectability was about 6 dB worse than when the signal was presented 325 ms after onset. By contrast, there was no such overshoot when S pi signals were presented at varying times after masker onset; detectability was about the same for all values of signal delay. Accordingly, the difference in performance between N o S o and N o S pi--the masking-level difference or MLD--was large (about 16 dB) with the shortest delays used and diminished (to about 9 dB) as the delay was increased. This absence of overshoot with the S pi signals is in accord with the well-established view that detectability in the dichotic masking conditions is based upon different stimulus information from that used in the diotic masking conditions. Specifically, the evidence confirms the common view that detectability in the diotic conditions is based more or less directly on neural firing rate, whereas, in the dichotic conditions, it is based upon interaural time differences encoded in the periodicity of neural firings.

Adult↗
PubMed1988

Partial dissociation of spontaneous otoacoustic emissions and distortion products during aspirin use in humans.

Otoacoustic emissions (OAEs) of two types--spontaneous and evoked distortion products--were studied before, during, and following a period of aspirin use. As previously reported, aspirin consumption uniformly reduced the spontaneous OAEs (SOAEs) to unmeasurable or extremely low levels. Aspirin consumption also reduced the amplitude of the evoked distortion products (EDPs) but did not eliminate them entirely. The amplitude of the EDP and its change with aspirin consumption were related to both the proximity of the EDP to the frequency of the SOAE and to the level of the primaries producing the EDP. At low primary levels, even with the SOAE absent (due to aspirin consumption, or suppression), EDPs near the SOAE frequency were 10-20 dB higher than when they were 100 Hz away from the SOAE frequency.

Acoustic Stimulation↗
PubMed1988

Temporary threshold shift measured with two psychophysical procedures.

Studies of temporary threshold shift (TTS) typically use classical psychophysical procedures, such as the method of adjustment, which are known to confound the obtained measure of sensitivity with the subject's criterion for response. A distinguishing feature of TTS research is high variability in the postexposure estimates of sensitivity, both within and across subjects and within and across sessions. It is possible that fluctuations in the subject's criterion for response (rather than actual variations in sensitivity) are responsible both for misestimations of the magnitude of the hearing loss induced by exposure to particular intense sounds (the TTS), and for the high variability that is commonly observed. To test this possibility, postexposure recovery of sensitivity was followed using two psychophysical procedures, one acknowledged to be criterion-dependent and the other relatively criterion-free. Within each postexposure session, alternate estimates of sensitivity were obtained with a version of the method of adjustment and with adaptive, two-interval forced-choice. The postexposure estimates of hearing sensitivity obtained with the two procedures were found to differ statistically; however, the preexposure baseline measures differed by essentially identical amounts. Thus, the values of TTS were equivalent with the two psychophysical procedures. Further, the session-to-session variability was found not to be significantly different with the two methods. Thus, for our trained observers at least, differences in pre- and postexposure response criteria did not appear to be a contaminating factor in estimates of TTS, and there was little basis for choice between the two procedures in regard to session-to-session variability.

Adult↗
PubMed1987

Comodulation detection differences using noise-band signals.

In a variant of the standard paradigm employed to study comodulation masking release (CMR), a narrow noise band was used as a signal in the presence of "cue" bands which had either the same or different temporal envelopes. The number of cue bands present ranged from zero to four; when there were two or four cue bands, they were either all presented at the same overall level or the spectral profile was "scrambled" in a haphazard manner. Different noise samples were presented within and across trials. The result was in the opposite direction from the standard CMR outcome; that is, better performance was obtained when the envelopes of the cue band(s) were uncorrelated with those of the signal band than when they were correlated. These comodulation detection differences (CDDs) ranged from a decibel or two up to 10-12 dB in different conditions, and were generally larger the more cue bands present. Standard CMR conditions, which were run as controls, revealed that the detectability of a tonal signal does not increase as the number of cue bands is increased from one to four-an outcome which differs from those obtained in profile analysis experiments. The data taken with the equal-level and the scrambled-level cues differed little in both the CDD and the CMR conditions. All noise bands were 100 Hz wide, and approximately 250 ms in duration. The signal band in CDD and the masker band in CMR were centered at 2500 Hz. The psychophysical procedure was two-interval forced choice.

Acoustic Stimulation↗
PubMed1987

Comodulation masking release in a forward-masking paradigm.

Waveforms that yield comodulation masking release (CMR) when they are presented simultaneously with a signal were used in a standard forward-masking procedure. The signal was a 25-ms sample of a 2500-Hz tone. The masker was a band of noise centered at 2500 Hz, 100 Hz in width, and 200 ms in duration. Presented with the masker were two or four cue bands, each 100 Hz wide and centered at various distances from the masker band. These cue bands either all had the same temporal envelope as the masker band (correlated condition) or their common envelope was different from that of the masker band (uncorrelated condition). In the initial experiments, (1) detectability of the tonal signal was 7-18 dB better when the masker band was accompanied by cue bands than when it was not--an effect that would be expected from past research on lateral suppression--but further, (2) the signal was about 3 dB more detectable in the correlated conditions than in the uncorrelated conditions. In follow-up experiments, these CMR-like differences between the correlated and uncorrelated conditions were substantially reduced (although not eliminated) by presenting a contralateral, wideband noise that was gated synchronously with the masker and/or cue bands. The implications are that the initial results were attributable in part to the "confusion effects" known to exist in certain temporal-masking situations, and that listeners are able to obtain greater information about the temporal extent of a masker band from correlated cue bands than from uncorrelated bands.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1987

Portal vein injury.

With the increasing number of traumatic injuries being seen in emergency departments, physicians must be aware of the less common and less obvious types of serious injury. Portal vein injury is serious (death rate 50%) and may be diagnosed only at laparotomy. Fortunately this injury is rare. Its management can be difficult, but an awareness of the possible methods of treatment could be life-saving. The authors report their experience with this injury and survey the literature on the subject.

Adolescent↗
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

Lupus glomerulonephritis with thrombotic microangiopathy.

Well-documented cases of systemic lupus erythematosus (SLE) with thrombotic microangiopathy (TMA) are rare. Renal biopsy in a 25-year-old woman with SLE who was in renal failure demonstrated proliferative lupus glomerulonephritis with arteriolar thrombosis and the arterial intimal changes of TMA. No staining of vessels for immunoglobulins or complement was found by direct immunofluorescence. Fibrillar and flocculent deposits were seen in the widened and rarefied subendothelial space in a small artery and two glomeruli, one of which also contained electron-dense deposits. The vascular findings, which are those of TMA, are distinct from the immune complex vasculopathy of SLE.

Adult↗
PubMed1986

Comodulation masking release: effects of varying the level, duration, and time delay of the cue band.

The phenomenon of comodulation masking release (CMR) was studied in a series of experiments. When the relative level of the correlated cue band was more than about 10 dB less than that of the masker band, the CMR was abolished. When the duration of the tonal signal was varied with continuous maskers and cues, the course of the standard temporal-integration function (about -10 dB/decade) was followed by both the correlated-cue and the uncorrelated-cue conditions. In a burst masker paradigm employing several burst durations, the data for the correlated-cue condition closely followed the previously determined temporal-integration function. Finally, when the cue band was time delayed more than about 1.6 ms, the CMR began to decline, and it was abolished somewhere between 3 and 15 ms of delay, depending upon the subject. This latter outcome was essentially the same for masker and cue bands of both 75 and 100 Hz in width; in neither instance was there evidence of a cyclic, autocorrelation-like pattern following the period of the envelope. Supplementary experiments revealed two facts: The detectability of a masked narrow-band signal is not improved by the simultaneous presence of a correlated (or uncorrelated) noise band, and a small CMR can be obtained under conditions of forward masking.

Acoustic Stimulation↗