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This study compared Modulation Detection Interference (MDI) in listeners with cochlear hearing loss and in listeners with normal hearing. The study was motivated by questions of temporal resolution in the listeners with cochlear hearing loss as well as by their general difficulty in monitoring target sounds in the presence of competing background noise. The first experiment was similar to the MDI paradigm of Yost and Sheft (1989) and showed an equivalence in performance between the two groups of listeners: MDI brought about by an interfering tone comodulated with the target tone at 10 Hz was about 11 dB in both groups. There was also no difference in MDI magnitude when the modulation rate of the interferer changed to 25 Hz, indicating a lack of tuning to differential modulation rate in the gated paradigm employed here. The second experiment was analogous in concept to the measurement of a psychophysical tuning curve; the depth of modulation of the interfering carrier was adjusted to just interfere with the detection of a suprathreshold degree of modulation on the target carrier. The listeners with cochlear hearing loss performed quite similarly to the normal group, and the general lack of a frequency effect for the carrier tones suggested that MDI was relatively insensitive to presumed differences in auditory filter bandwidth between listeners. Because the basis of MDI has been hypothesized to be the fusion of the interfering tone with the target tone, the results of this study suggest that the auditory grouping factors presumed to underlie MDI are intact in listeners with hearing loss of cochlear origin.

Previous studies have indicated that the masking-level difference is reduced in listeners having conductive hearing loss, even when sensation level is controlled. According to the crosstalk hypothesis, this deficit can be explained in terms of reduced binaural cues at the level of the cochleas, due to acoustic contributions from the bone conduction route. It is possible that such a deficit can be overcome through the use of insert earphones, because such transducers provide a high degree of interaural attenuation. In this study, NoSo and NoS tau thresholds were measured in normal-hearing subjects and in subjects having hearing loss due to otosclerosis, using both standard TDH earphones encased in NAF-48490-1 circumaural cushions and deeply seated Etymotic 3A insert earphones. Masking noise was presented both at a fixed sound-pressure level and at a fixed sensation level. The results did not indicate consistently larger MLDs with insert earphones for either group of subjects, for either type of presentation level. The MLDs of the hearing-impaired subjects often remained abnormally small even when the insert transducers were used and the noise was presented at a fixed SL. Whereas acoustic crosstalk appeared to have a role in the results obtained, other factors (perhaps related to long-term hearing threshold asymmetry and/or interaural phase mismatch) also were apparently involved.

This study measured the masking level difference (MLD) for both 500-Hz tone detection and spondee word recognition in two groups of listeners. One group consisted of 9 elderly listeners with normal audiometric sensitivity bilaterally, up to at least 2000 Hz. The other group was a control group of 10 young listeners with normal hearing. The intent was to determine whether the elderly listeners exhibited a reduction in binaural performance that might contribute to the difficulties many such listeners have in understanding speech in noisy situations. By measuring MLDs in elderly listeners in the absence of marked peripheral hearing loss, it was hoped that any observed changes in MLD could be more strongly attributed to central effects. For both tone detection and speech recognition, it was found that the elderly performed more poorly than the young listeners, primarily on the NoS pi condition.

Comodulation masking release (CMR) was investigated in normal-hearing and cochlear-impaired listeners. The narrow-band masker centered on the tonal signal was flanked by a series of other narrow noise bands, some of which had temporal envelopes that were the same as that of the on-signal band (comodulated bands) and some of which had different temporal envelopes (codeviant bands). Previous research using such stimuli with normal-hearing listeners indicated that CMR was often substantially reduced when two codeviant bands were present at spectral locations close to the signal frequency, but that CMR recovered to some extent when more codeviant bands were added. In the present study, cochlear-impaired listeners showed an abnormally large reduction in CMR when codeviant bands were present, and poorer recovery of CMR with increasing number of codeviant bands. Supplementary experiments suggested that the poor recovery of CMR with increasing number of codeviant bands may have been due to the small range (in dB) over which CMR could occur in cochlear-impaired listeners. It is possible that abnormal reduction in CMR with codeviant bands present was due to poor peripheral analysis in hearing-impaired listeners.

Monaural envelope correlation perception was investigated in listeners with normal hearing and in listeners with cochlear hearing loss. Using a three-interval forced-choice procedure, the task of the subject was to identify the one interval out of three where the noise bands had correlated envelopes. Performance was determined as a function of the spectral separation between noise bands (delta f of 250, 500, or 1000 Hz) and the number of noise bands present (two, three, or five). Although individual differences existed, the results generally indicated better performance for the listeners with normal hearing when the delta f between bands was relatively small; however, there was no significant effect of hearing loss when the frequency separation between bands was greater than 250 Hz. The listeners with normal hearing generally showed decreased performance with increasing delta f, whereas the performance of many of the listeners with hearing impairment usually did not change appreciably with variation in delta f. Both groups of listeners showed improved performance with increasing number of noise bands present for the 500-Hz delta f. Only the listeners with hearing impairment showed significantly improved performance with increasing band number for the 250-Hz delta f; neither group showed improved performance with increasing band number for the 1000-Hz delta f. With five bands present, the performance of the listeners with hearing impairment did not differ significantly from that of the listeners with normal hearing, even for the 250-Hz delta f.(ABSTRACT TRUNCATED AT 250 WORDS)

The masking-level difference (MLD) was measured in a group of adult listeners having unilateral otosclerosis before stapedectomy surgery, 1 month following surgery, and 1 year following surgery. The results indicated that the MLD in this group improved significantly over each of the sequential tests. In contrast, for a group of normal-hearing listeners, the MLD did not change significantly over sequential testing. The results support an interpretation that a period of exposure to abnormal binaural auditory input (as occurs in a unilateral conductive loss) can blunt sensitivity to binaural cues after normal binaural input has been restored in most adult listeners, however, there appears to be a relatively long-term readjustment or adaptation, such that the sensitivity to binaural cues recovers to a normal or near-normal level at the 1-year postsurgery retest. Two of eight listeners did not show recovery to a normal MLD value over this time period. The efficiency and rate of readjustment may differ among individuals.

1. Kinins exert a contractile effect on rabbit aortic rings via the stimulation of B1 receptors. Des-Arg9-bradykinin (BK) is more potent than BK on this receptor type. The mode of action of des-Arg9-BK on rabbit aortic tissue has been studied by both the aortic ring contractility assay and a cellular model using cultured aortic smooth muscle cells (SMCs). 2. The des-Arg9-BK-induced contractions in rabbit aortic rings were unaffected by pretreatments with nifedipine, indomethacin, REV-5901 (a 5-lipoxygenase blocker) and LY-83583 (a guanylyl cyclase inhibitor); however, the protein kinase inhibitors H-7 and H-9 significantly reduced the maximal effect of des-Arg9-BK. 3. The contractile responses to des-Arg9-BK in calcium-free Krebs solution were slightly but not significantly attenuated in amplitude, as compared to paired control tissues bathed in Krebs solution, and sustained plateaus of contraction were observed in the absence of Ca2+. However, Ca2+ replenishment further increased the kinin-induced contraction measured in Ca(2+)-free bathing fluid. 4. Despite the lack of evidence of a mediating role for prostaglandin in the mechanical response to des-Arg9-BK, the kinin stimulated the release of prostacyclin from rabbit aorta rings measured as immunoreactive 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha). 5. Smooth muscle cells (SMCs) derived from the rabbit aorta exhibit functional responses to des-Arg9-BK in acute release of 6-keto-PGF1alpha and of inositol phosphate turnover which were inhibited by pretreatment with the B1 receptor antagonist, Lys[Leu8]des-Arg9-BK, but not by the B2 receptor antagonist, Hoe-140. Preincubation of the cells with interleukin- 1 (IL-1) 20 h before stimulation with the kinin had no effect on basal inositol phosphate turnover, but potentiated the acute effect of des-Arg9-BK.6. These results suggest that second mesengers derived from the action of phospholipase C are produced by SMCs when B1 receptors are activated in rabbit aortic tissue. Intracellular calcium stores are primarily mobilized by des-Arg9-BK, although receptor-controlled calcium influx has not been ruled out, and may contribute to initiate the contractile responses. The maintenance of the contractile state involves protein kinase C activity and is consistent with a current model of SMC function. The cell model retains some of the cardinal properties of B1 receptor-mediated vascular responses: endothelium independent PGI2 release and up-regulation by the cytokine IL-1. PGI2 is not involved in the mechanical response, possible because the rabbit aorta is refractory to this prostaglandin.

Common amplitude modulation across frequency facilitates comodulation masking release (CMR) and may also contribute to auditory grouping. The purpose of the present investigation was to determine whether there is an association between these two phenomena; that is, does the occurrence of CMR require that the comodulated noise bands making up the composite masker be grouped together? Three experiments were undertaken, each manipulating one variable designed to hinder the fusion of the comodulated noise bands. In experiment 1, the variable of onset/offset asynchrony was observed to have a marked effect: CMR could be completely abolished if the asynchrony between the on-signal band and the flanking bands was sufficiently great (> or = 50 ms). In experiment 2, an auditory streaming paradigm was employed and this was observed to disrupt CMR significantly. However, a substantial CMR remained. Experiment 3 attempted to hinder the fusion of the comodulated noise bands by drawing the various noise bands into separate harmonic series. However, the small effect observed did not appear to be due to a parsing of the fused image. Results from experiments 1 and 2 suggest that the CMR mechanism does not act in isolation from the processes that give rise to auditory object formation. In particular, the cue of onset/offset synchrony appears to be of paramount importance.

This study investigated the development of temporal resolution as a function of frequency region using a modified masking period pattern paradigm. This paradigm also allowed age-dependent comparisons of within-channel (temporal resolution) versus across-channel (comodulation masking release [CMR]) processing of temporal information to be made in the same listeners. The results indicated that temporal resolution improves with age. At low frequencies, this improvement continues beyond 10 years of age, whereas at high frequencies performance approaches adult levels by about age 6. Although it is reasonable to expect an association between CMR and temporal acuity, the measure of CMR did not show a significant age effect. The possibility was raised that the poorer temporal resolution of children may not reflect simply a deficiency in peripheral processing of temporal information.

Experiments 1 and 2 investigated the effect of frequency selectivity on comodulation masking release (CMR) in normal-hearing subjects, examining conditions where frequency selectivity was relatively good (low masker level at both low [500-Hz] and high [2500-Hz] signal frequency, and high masker level at low signal frequency) and where frequency selectivity was somewhat degraded (high masker level and high signal frequency). The first experiment investigated CMR in conditions where a narrow modulated noise band was centered on the signal frequency, and a wider comodulated noise band was located below the band centered on the signal frequency. Signal frequencies were 500 and 2000 Hz. The masker level and the frequency separation between the on-signal and comodulated flanking band were varied. In addition to conditions where the flanking band and on-signal band were presented at the same spectrum level, conditions were included where the spectrum level of the flanking band was 10-dB higher than that of the on-signal band, in order to accentuate effects of reduced frequency selectivity. Results indicated that CMR was reduced at the 2000-Hz region when masker level was high, when the frequency separation between on-signal and flanking band was small, and when a 10-dB level disparity existed between the on-signal and flanking band. In the second experiment, CMR was investigated for narrow comodulated noise bands, presented either without any additional sound or in the presence of a random noise background. CMR increased slightly as the masker level increased, except at 2500 Hz when the noise background was present. The decrease in CMR at 2500 Hz with the high masker level and with a noise background present could be explained in terms of reduced frequency selectivity. In a third experiment, we compared performance for equal absolute bandwidth maskers at a low (500-Hz) and a high (2000-Hz) stimulus frequency. Results here suggested that detection in modulated noise may be reduced due to a reduction in the number of quasi-independent auditory filters contributing temporal envelope information. The effects found in the present study using normal-hearing listeners under conditions of degraded frequency selectivity may be useful in understanding part of the reduction of CMR that occurs in cochlear-impaired listeners having reduced frequency selectivity.

This study investigated the masking-level difference (MLD) and auditory brainstem response (ABR) in a group of children with a history of otitis media with effusion (OME) and a control group of children with no known history of ear disease. All children had normal hearing at the time of testing. The main goal of the study was to determine whether there was an association between a reduced MLD in the OME children and an abnormal ABR (in terms of prolonged absolute or interwave intervals, or interaural differences in the ABR waveforms). The results indicated that the group of children having a history of OME had significantly reduced MLDs and had significantly prolonged waves III and V, and I-III and I-V interwave intervals. The correlations between MLD and delays in absolute wave or interwave intervals were not significant. However, some correlations between interaural asymmetries of the interwave intervals and the MLD were significant. The results suggest that the reduction in MLD found in children having a history of OME may be related to abnormal brainstem processing.

In random noise, masking is influenced almost entirely by noise components in a narrow band around the signal frequency. However, when the noise is not random, but has a modulation pattern which is coherent across frequency, noise components relatively remote from the signal frequency can actually produce a release from masking. This masking release has been called comodulation masking release (CMR). The present research investigated whether a similar release from masking occurs in the analysis of a suprathreshold signal. Specifically, the ability to detect the presence of a temporal gap was investigated in conditions which do and do not result in CMR for detection threshold. Similar conditions were investigated for the masking level difference (a binaural masking release phenomenon). The results indicated that suprathreshold masking release for gap detection occurred for both the masking-level difference (MLD) and for CMR. However, masking release for gap detection was generally smaller than that obtained for detection threshold. The largest gap detection masking release effects obtained corresponded to relatively low levels of stimulation, where gap detection was relatively poor.

The hormonal regulation of sodium and volume homeostasis was investigated in three patients (two related) with the syndrome of familial hyperkalemic acidosis and hypertension with normal glomerular filtration rate. Recumbent plasma renin activity was low during normal sodium intake (135 mmol daily), and the response to upright posture or to low sodium diet (10 mmol daily) was blunted. Recumbent plasma aldosterone levels were normal in two patients and high in one, and the standing values were elevated in one; responses to upright posture were brisk on low sodium diet. Angiotensin II infusion induced a marked increase in plasma aldosterone. Plasma atrial natriuretic peptide was at the upper limit of normal during normal sodium intake, decreased during diuretic therapy, and increased during sodium chloride infusion in one patient. Basal urinary prostaglandin E2, prostaglandin F2 alpha, and 6-ketoprostaglandin F1 alpha excretion rates were decreased, and thromboxane B2 was increased. Total blood and plasma volumes were subnormal, whereas extracellular fluid volume and exchangeable sodium values were close to or above (in one patient) the mean normal values. Chronic treatment with hydrochlorothiazide in two patients corrected the hyperkalemic acidosis and hypertension, but on its discontinuation (in one patient) all biochemical abnormalities promptly reappeared.

Temporal gap detection was measured as a function of absolute signal bandwidth at a low-, a mid-, and a high-frequency region in six listeners with normal hearing sensitivity. Gap detection threshold decreased monotonically with increasing stimulus bandwidth at each of the three frequency regions. Given conditions of equivalent absolute bandwidth, gap detection thresholds were not significantly different for upper cutoff frequencies ranging from 600 to 4400 Hz. A second experiment investigated gap detection thresholds at two pressure-spectrum levels, conditions typically resulting in substantially different estimates of frequency selectivity. Estimates of frequency selectivity were collected at the two levels using a notched-noise masker technique. The gap threshold-signal bandwidth functions were almost identical at pressure-spectrum levels of 70 dB and 40 dB for the two subjects in experiment II, while estimates of frequency selectivity showed poorer frequency selectivity at the 70-dB level than at 40 dB. Data from both experiments indicated that gap detection in bandlimited noise was inversely related to signal bandwidth and that gap detection did not vary significantly with changes in signal frequency over the range of 600 to 4400 Hz. Over the range of frequencies investigated, the results indicated no clear relation between gap detection for noise stimuli and peripheral auditory filtering.

This study sought to determine whether speech recognition in a modulating noise background can be facilitated by a process attributable to comodulation masking release (CMR). Experiment 1 examined the masked identification of six filtered vowels as a function of the number of comodulated noisebands present. A benefit of increased number was observed, consistent with an interpretation in terms of CMR, although it could not be certain that the basis of the discrimination was word recognition in the semantic sense. Experiment 2 made use of a forced-choice rhyming test in which the response foils differed only in a single filtered consonant; again, the measure of interest was performance as a function of the number of comodulated noisebands present. No evidence for a suprathreshold CMR was observed. Experiment 3 made use of open-set sentence material and employed a different paradigm, which allowed a measure of CMR in terms of the difference between thresholds in correlated and uncorrelated noise to be determined. While a CMR for speech detection was observed, no CMR for speech recognition was found. It was concluded that CMR is most evident in masked detection tasks and that diminishing returns are encountered as the signal-to-masker ratio is raised.

The ability to detect the existence of amplitude modulation at a target frequency is reduced when amplitude modulation exists at a flanking frequency. This effect has been termed modulation detection interference (MDI) [Yost and Sheft, J. Acoust. Soc. Am. 85, 848-857 (1989)]. One explanation for MDI holds that the masking and target frequencies are grouped together by the auditory system such that it is difficult to analyze the modulation at each frequency separately. The present study investigated conditions where the asynchrony of temporal gating of the target and flanking frequencies was manipulated in order to make the frequencies more or less likely to be grouped together by the auditory system and perceived as originating from a single putative source. A second experimental manipulation attempted to perceptually segregate the masking and target frequencies on the basis of harmonicity or spectral proximity. The results of the experiments indicated that manipulations that were intended to enhance the segregation of the masking and target frequencies reduced the magnitude of MDI effects. This generally supported an interpretation that MDI is related in some way to auditory grouping. A final experiment was performed in which the subject had to detect the presence of amplitude modulation, but also had to identify which of two frequency components carried the modulation. Subjects were often poor in discriminating which of two frequencies was amplitude modulated, even when the modulation itself was clearly audible. It was concluded that part of the MDI effect might be due to the poor ability of the auditory system to associate modulation with the carrier of the modulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Linoleic acid and fish oil omega-3 fatty acids, but not arachidonic acid, exerted antihypertensive effects in a model of angiotensin II-induced hypertension in rats. Indomethacin did not influence the systolic arterial pressure of arachidonic acid-treated hypertensive rats whereas compound L-641,953, a prostaglandin H2/thromboxane A2 receptor antagonist, caused a notable but statistically nonsignificant decrease in blood pressure in these animals. Although these results do not exclude entirely the possibility that the lack of antihypertensive effect of arachidonic acid may be due, in part, to the concomitant formation of vasoconstrictor prostanoids, they do not support it. These observations, as well as those of a previous study, indicate that linoleic acid and fish oil omega-3 fatty acids exert antihypertensive effects of their own, independently of the prostanoid system, and that these properties are not shared by arachidonic acid.

To study the modulatory role of renal eicosanoids on renal hemodynamics and electrolyte excretion, pressor doses of norepinephrine (NE) were infused in 10 control subjects (mean age, 26 y) and 13 patients (mean age, 25 y) with borderline hypertension. The highest NE dose used (150 ng/kg/min) produced comparable increases in mean blood pressure in control subjects (20 +/- 2 mmHg) and in patients (23 +/- 3 mmHg). NE induced a significant increase in renal vascular resistance (p less than 0.01, both groups), with a smaller decrease in glomerular filtration rate resulting in a concomitant increase in filtration fraction (p less than 0.01, both groups). The renal hemodynamic changes tended to be more pronounced in borderline hypertension. NE infusion led to similar decreases in electrolyte clearances in the two groups. Urinary prostaglandin (PG)E2, PGF2 alpha (p less than 0.01), and 6-keto-PGF1 alpha increased with NE infusion. Urinary thromboxane (TX)B2 increased slightly in control subjects and decreased in borderline hypertension (p less than 0.05). The 6-keto-PGF1 alpha/TXB2 ratio, an index of vasodilation, was significantly increased (p less than 0.05) in borderline hypertension. These results demonstrate that in both groups pressor infusion of NE induced significant modifications in renal hemodynamics and in urinary electrolyte and eicosanoid excretion. The vasodilatory component of the renal eicosanoid system appears hyperresponsive in borderline hypertension, which may represent an early antihypertensive defense mechanism.

This study sought to differentiate between the effect of stimulus bandwidth and the effect of number of activated auditory channels on gap detection in narrow bands of noise. The aim was to clarify the role of across-frequency analysis in temporal processing. Experiment 1 established that when total noise bandwidth is held constant at 100 Hz, gap detection improves as stimulus energy is distributed to both lower and higher frequencies. Experiment 2a showed that the effect was smaller, or was absent, when the cumulative stimulus bandwidth was increased from 100 to 200 Hz. Experiment 2b confirmed that the benefit of spectral dispersion for the narrower cumulative bandwidth also held for a higher frequency region. The results suggest that in conditions where the cumulative stimulus bandwidth is relatively narrow and, concomitantly, gap detection is relatively poor, there is an advantage in dispersing the stimulus across a number of auditory channels. The advantage for the distribution of energy across a range of auditory channels may be offset when the spectral spacing of bands exceeds a critical value.

Cromakalim, a novel potassium channel-activating drug, was administered for a 3-day period in eight untreated hospitalized patients with established hypertension. The fixed and single dose of 1.5 mg/day produced a significant reduction in systolic and diastolic blood pressure with a small increase in heart rate. Glomerular filtration rate was unchanged and effective renal plasma flow was slightly increased with a concomitant small decrease in filtration fraction and in renal vascular resistance. No significant change was observed in urinary prostaglandin (PG)E2, PGF2 alpha, and thromboxane B2, while 6-keto-PGF1 alpha (the stable metabolite of prostacyclin) rose from 189 +/- 6 to 368 +/- 115 ng/day. The renal excretion of 6-keto-PGF1 alpha correlates with the modification observed in renal plasma flow, suggesting a compensatory role for prostacylin in preserving renal hemodynamics during antihypertensive therapy with cromakalim.

Comodulation masking release (CMR) is a phenomenon that demonstrates the sensitivity of the auditory system to across-frequency differences in the temporal modulation pattern of a complex waveform. In this paper, we review briefly some of the data on the physical parameters that affect CMR and describe models that have been proposed to account for CMR--namely, models based upon envelope equalization/cancellation, across-frequency envelope correlation, and "dip listening". The present literature is ambiguous with regard to the relative importance of energy in the peak and dip regions of the waveform envelope. We therefore performed a series of experiments to investigate this issue. In the first experiment, we examined CMR for signals that resulted either in a uniform increment or in uniform decrement in the masking noise centred on the signal frequency. This was accomplished by using a 20-Hz-wide noise band centred on 700 Hz as both the masker and as the signal, adjusting the phase angle between the signal and masker to either 0 degree (increment) or 180 degrees (decrement). Conditions were examined where either zero, one, two, four, or six comodulated flanking bands were present. Results indicated positive CMRs for all conditions in which a comodulated flanking band was present. CMR increased as the number of flanking bands increased for intensity increments, but not for intensity decrements. The remaining experiments examined conditions where signals were present only in masker peaks, or only in masker dips. The results of these experiments indicated relatively large CMRs when the signal occurred in dip regions, but no CMR when the signal occurred in peak regions. Whereas some of the results of the above experiments would be difficult to account for in terms of the dip listening hypothesis of CMR, the present findings did indicate that the stimulus cues that give rise to CMR appear to be derived primarily from the dip regions of the masking noise.

The masking-level difference (MLD) was investigated in a group of children having no known history of ear disease, and a group of children having a history of otitis media with effusion and hearing loss. The MLD is a psychoacoustic measure of the sensitivity of the auditory system to subtle interaural difference cues of time and amplitude and relates to the ability of the listener to detect and to recognize signals in noisy backgrounds. In the otitis media with effusion group, MLDs were measured both before and 1 and 3 months after the placement of pressure equalization tubes. The MLDs were often abnormally small in the otitis media with effusion group before surgery, when hearing loss was present. Significantly, MLDs sometimes remained abnormally small after surgery (after normal hearing had returned). The postsurgery MLD was particularly likely to be abnormally reduced in subjects who had experienced asymmetric losses of hearing.

Three experiments were performed to examine the development of frequency selectivity and to attempt to separate peripheral versus central contributions to frequency selectivity. In Experiment 1, frequency selectivity was examined in 4-year-old children, 6-year-old children, and adults, using a fixed-masker-level, notched-noise masking method. Thresholds were determined in a no-notch condition and in conditions in which the notchwidth was 0.3 times the center frequency (0.3 x fc) or 0.6 x fc. The results for the adults and 6-year-olds were similar, but the notched-noise functions of the 4-year-old listeners were relatively shallow. These results were consistent with an interpretation that frequency selectivity is relatively poor in 4-year-old listeners; however, the results of the 4-year-old listeners might also be accounted for in terms of poor processing efficiency. For example, the children may require a relatively high level of signal-related excitation in order for detection to occur. If the growth of excitation is steeper in the no-notch condition than in notched-noise conditions, then thresholds in the notched-noise conditions might be elevated because of poor processing efficiency rather than poor frequency selectivity. This interpretation is consonant with past data showing that the growth of loudness of partially masked signals steepens as a function of increasing masker level: The masker level at the output of the auditory filter centered on the signal frequency would be less for the notched-noise masker than for the masker having no notch. In Experiment 2 the growth of loudness was examined for three adult listeners in the no-notch condition and the 0.6 x fc notched noise. Results showed a steeper growth of loudness in the no-notch case. In Experiment 3, a notched-noise measure of frequency selectivity was used in which the signal level was fixed at 15 dB SL and the masker level was varied adaptively. In this method the noise level at the output of the auditory filter centered on the signal should theoretically be constant over the different notch conditions. Adult and 4-year-old listeners were tested. The notched-noise functions were similar between the adult and 4-year-old listeners. This result supports an interpretation that the shallow notched-noise, fixed-masker-level functions of 4-year-old children may be due to poor processing efficiency rather than to poor peripheral frequency selectivity.

Factors that are chemotactic for phagocytic leukocytes are known to elicit important acute circulatory changes, and the role of circulating leukocytes in these models is controversial. To evaluate the role of the blood vessel wall in the absence of circulating cells, spiral strips of human umbilical artery were exposed in vitro to the chemotactic peptides f-Met-Leu-Phe (1-100 nM) or C5a (2.5-25 nM). Contractile responses were observed for both peptides. Certain agonist analogues and a selective antagonist of the chemotactic action of f-Met-Leu-Phe behaved correspondingly as agonists and antagonist of the contractile effect on umbilical artery. The anaphylatoxin C3a also exerted a contractile effect on the tissue (25 nM and above), but this effect was highly tachyphylactic. Inhibitory drugs were used to examine the contributions of secondary mediators in eliciting the effects of C5a and f-Met-Leu-Phe. The contractile effect of both peptides was massively inhibited either by indomethacin or the thromboxane A2/prostaglandin H2 antagonist SQ 29548. Dazmegrel, a thromboxane A2 synthetase inhibitor, had partial inhibitory effects on contractions induced by either peptide. The contractile effect of C3a was prevented by indomethacin pretreatment. Vascular strips did not release measurable histamine in the bathing fluid after challenge with C5a or f-Met-Leu-Phe. The tissue apparently contains neither histamine nor mast cells. Autoradiography of 125I-labeled C5a or f-Met-Leu-Phe analogue showed specific binding of the peptides to cells dispersed in the vessel wall, but more frequently at the periphery. Cells stained positively for alpha-naphthyl acetate esterase showed a similar distribution. Pure cultures of smooth muscle cells derived from the umbilical artery failed to release prostanoids when exposed to f-Met-Leu-Phe or C5a, whereas fresh strips of this artery released more thromboxane B2 than the baseline in response to these peptides. We conclude that macrophagelike cells, present in the vessel wall, are the likely target cells for the chemotactic peptides. These cells trigger a contractile effect of the smooth muscle by generating cyclooxygenase products.

This paper examines some of the factors that can affect the magnitude of comodulation masking release (CMR). In experiment I, psychometric functions were measured for the detection of a 1-kHz sinusoidal signal in a "multiplied" narrow-band noise centered at 1 kHz (reference condition) and the same noise with two comodulated flanking bands added. The functions were slightly steeper for the comodulated than for the reference masker. Thus CMRs measured at a high percent correct point were slightly (0.4 dB) larger than CMRs measured at a low percent correct point. Large individual differences were found for the reference masker but not for the comodulated masker. Experiment II compared CMRs obtained with narrow-band Gaussian noise and multiplied noise, using a single flanking band. For a flanking band remote from the signal frequency, the CMRs were smaller and more variable for the multiplied noise than for the Gaussian noise. This variability arose mainly from individual differences in the reference condition. Experiment III compared growth-of-masking functions for a signal centered in Gaussian noise and multiplied noise. Thresholds were lower for the multiplied than for the Gaussian noise, and the differences were greatest at high noise levels. The results are consistent with the idea that, for multiplied noise, some subjects can detect a change in the distribution of the envelope of the stimulus, when the signal is added to the masker. Such subjects have low thresholds in the reference condition, and give small CMRs. Other subjects are relatively insensitive to this cue. They have higher thresholds in the reference condition, and give larger CMRs. For Gaussian noise, thresholds for the reference condition are relatively stable across subjects and CMRs tend to be substantial, even for flanking-band frequencies remote from the signal frequency.

A series of three experiments was undertaken to investigate detection of sinusoidal frequency modulation (FM) in the presence of FM at a separate frequency. The first experiment measured detection of modulation for an FM tone with a modulation frequency (fm) of 6 Hz as a function of carrier frequency (fc) under three conditions: (1) in quiet, (2) in the presence of a 2500-Hz pure tone, and (3) in the presence of a 2500-Hz FM tone with fm = 6 Hz, modulating in phase with the signal. Detection of FM in the presence of the second FM tone was worse than for either the signal presented in quiet or in the presence of the unmodulated tone. Threshold varied as an inverse function of frequency separation between the signal and the masker. In the second experiment, FM detection for a signal with fc = 1900 Hz and fm = 6 Hz was measured as a function of the modulation frequency (fm = 2-18 Hz) of the 2500-Hz masker tone. FM detection improved significantly with increasing difference between the modulation frequencies of the signal and the masker. The final experiment measured detection of FM for a signal (fc = 1900 Hz, fm = 6 Hz) in the presence of a second FM tone (fc = 2500 Hz, fm = 6 Hz) as a function of the relative phase of the 6-Hz modulators. Detection of FM improved monotonically as a function of increasing phase difference between the two modulators. The results are discussed in terms of modulation detection interference and perceptual grouping.

A series of four experiments was undertaken to ascertain whether signal threshold in frequency-modulated noise bands is dependent upon the coherence of modulation. The specific goal was to determine whether a masking release could be obtained with frequency modulation (FM), analogous to the comodulation masking release (CMR) phenomenon observed with amplitude modulation (AM). It was hypothesized that an across-frequency grouping process might give rise to such an effect. In experiments 1-3, maskers were composed of three noise bands centered on 1600, 2000, and 2400 Hz; these were either comodulated or noncomodulated with respect to both FM and AM. In experiment 1, the modulation was sinusoidal, and the signal was a 2000-Hz pure tone; in experiment 2, the modulation was random, and the signal was an FM noise band centered on 2000 Hz. The results obtained showed that, given sufficient width of modulation, thresholds were lower in a coherent FM masker than in an incoherent FM masker, regardless of the pattern of AM or signal type. However, thresholds in multiband maskers were usually elevated relative to that in a single-band masker centered on the signal. Experiment 3 demonstrated that coherent FM could be discriminated from incoherent FM. Experiment 4 gave similar patterns of results to the respective conditions of experiments 2 and 3, but for an inharmonic masker with bands centered on 1580, 2000, and 2532 Hz. While within-channel processes could not be entirely excluded from contributing to the present results, the experimental conditions were designed to be minimally conducive to such processes.

Past research has indicated that binaural hearing abilities are not always normal in patients having otosclerosis who have received bilaterally normal pure-tone thresholds through stapedectomy. This study investigated whether poststapedectomy performance on the binaural masking-level difference test could be predicted from presurgery tests in which the two ears were stimulated at an equal sound pressure level and at an equal sensation level. Results indicated that (1) binaural hearing usually improved following stapedectomy, though some patients maintained abnormally poor binaural hearing even though postsurgery pure-tone thresholds were normal; and (2) prediction of postsurgery results was poor, with postsurgery results often being underestimated from presurgery results. Results are interpreted in terms of possible forms of auditory deprivation and acoustic crossover.

The detectability of a pure-tone signal masked by a band of noise centered on the signal can be improved by the addition of flanking noise bands, provided that the temporal envelopes of the flanking bands are correlated with that of the on-signal band. This phenomenon is referred to as comodulation masking release (CMR). The present study examined CMR in conditions in which some flanking noise bands were comodulated with the on-signal band, but other flanking bands (termed "deviant" bands) were not. Past research has indicated that CMR is often substantially reduced when deviant bands are present at spectral locations close to the signal frequency. An investigation was undertaken to determine whether the disruptive effects of such bands could be reduced by factors related to auditory grouping. The signal frequency was 100 Hz. In one condition, only 20-Hz-wide comodulated bands, centered on 400, 600, 800, 1000, 1200, 1400, and 1600 Hz, were present. The CMR for this condition, referenced to threshold for the on-signal band only, was approximately 15 dB. In a second condition, two deviant bands were added at 900 and 1100 Hz; their presence reduced the CMR to only 3-4 dB. The number of deviant bands was then increased progressively, from two to eight bands. Deviant bands either shared a common envelope (codeviant), or had unique envelopes (multideviant). The number of bands that were comodulated with the on-signal band was held constant at six.(ABSTRACT TRUNCATED AT 250 WORDS)

Comodulation masking release (CMR) was investigated as a function of signal frequency (0.5-4.0 kHz) and the total bandwidth of noise centered on the signal frequency. Taking noncomodulated noise of the same bandwidth as the reference condition, CMR for modulated noise increased with increasing bandwidth of the flanking noise outside the critical band centered on the signal tone; however, this growth asymptoted for broad total bandwidths. These bandwidth effects were expressed by scaling the width of the flanking bands beyond the critical band centered on the signal frequency, approximately according to a critical bandwidth scale. After this scaling, signal frequency had negligible effect on CMR magnitude. For the low modulation frequencies involved, a beneficial effect on CMR at high carrier frequencies would not be expected, and none was observed. Some further trends in the masked thresholds in comodulated and noncomodulated conditions, and the choice of appropriate reference condition are discussed.

The masking-level difference (MLD) was investigated in children aged 3.9 to 9.5 years and in an adult control group in order to examine the development of the MLD with age. A three-alternative forced-choice adaptive tracking procedure was used for all listeners. MLDs were determined for a 500-Hz pure-tone signal presented in a 300-Hz-wide masking noise centered on 500 Hz, where both interaural time and amplitude cues were present, and in 40-Hz-wide maskers centered on 500 Hz, where either amplitude (MLD delta a) or time (MLD delta t) cues were present. The masking noise level was fixed at 60 dB/Hz SPL. For the 300-Hz-wide masker, the MLDs of the children increased in magnitude up until the age of 5 or 6 years. For the 40-Hz-wide maskers, the MLDs of the 5- and 6-year-old children were still somewhat below adult values. It is possible that these differences between adults and children are related to the development of the peripheral/brainstem auditory system. By this interpretation, the MLD might be small in young listeners because the interaural time and amplitude cues underlying the MLD are coded with relatively poor precision. However, it is perhaps more likely that these differences are coded precisely in the peripheral auditory system, but that more central auditory processes are relatively inefficient in extracting the interaural information.

NoSo and NoS pi detection thresholds for a 500-Hz pure-tone signal were measured as a function of masking noise bandwidth in normal-hearing and cochlear hearing-impaired subjects. NoSo and NoS pi critical bands were derived from the bandlimited noise functions. A notched noise measure of the monaural critical band was also obtained for each ear. One hypothesis tested was that an asymmetrical monaural critical band would result in a relatively steep improvement of the NoS pi detection threshold as a function of decreasing masker bandwidth and would, therefore, be associated with a wider binaural critical band. This was hypothesized because the outputs of the left and right auditory filters would be more decorrelated the greater the interaural difference in the monaural critical band. However, as the noise bandwidth was narrowed, the decorrelation would lessen, resulting in a relatively steep improvement in NoS pi detection. Results indicated that the masking level difference (MLD) was smaller and that the monaural critical bands were generally wider in cochlear-impaired listeners. NoSo and NoS pi critical bands were somewhat larger in the cochlear hearing-impaired listeners having relatively wide monaural critical bands. There was a significant correlation between monaural critical band asymmetry and the NoS pi critical band; however, this correlation was insignificant when a control was employed for the critical band in the worse ear. Therefore, the present results did not support a strong association between monaural critical band asymmetry and the width of the NoS pi critical band.

The aim of this study was to examine whether the scheme of across-frequency comparison underlying comodulation masking release (CMR) is sensitive to the placement of the signal in the array of comodulating bands. This was addressed using the paradigm of signal-frequency uncertainty. In the first experiment, maskers were constructed of linearly spaced sinusoidally amplitude-modulated tones, and the signal was a pure tone presented at one of five frequencies. A small uncertainty effect was observed for the noncomodulated masker, but no significant effect was observed for the comodulated masker. In the second experiment, the maskers were constructed of logarithmically spaced noise bands, and the signal was a pure tone presented at one of seven frequencies. In these conditions, an uncertainty effect was observed in both noncomodulated and comodulated maskers, which was larger than that observed in experiment 1. The results were interpreted as indicating that the mechanism of across-frequency comparison underlying CMR is sensitive to signal location.

Frequency selectivity and comodulation masking release (CMR) for a 1000-Hz signal frequency were examined in 6-year-old children and adults. An abbreviated measure of frequency selectivity was also conducted for a 500-Hz signal. Frequency selectivity was measured using a notched-noise masking method, and CMR was measured using narrow bands of noise whose amplitude envelopes were either uncorrelated or correlated. There were 6 listeners in each age group. No differences were observed between the adults and children for either auditory measure. Similarly, no differences were observed in the ability to detect a pure-tone signal in a relatively wideband noise masker. When the masking noise was narrowband, however, the masked thresholds of the children were higher than those of the adults. Two characteristics that distinguish narrowband noise from wideband noise are: (1) narrowband noise has a pitch quality corresponding to its center frequency, whereas wideband noise does not have definite pitch; (2) the intensity fluctuations are relatively greater in narrowband noise than in wideband noise. This may suggest that 6-year-old children have a reduced ability to detect signals in noise backgrounds where the signal has perceptual qualities similar to the noise, or in noise backgrounds having a high degree of fluctuation.

The goal of this study was to determine the role of prostanoids in a new model of mineralocorticoid-dependent hypertension induced by the subcutaneous infusion of aldosterone (1 micrograms/hr) to normal male Sprague-Dawley rats. This regimen caused a mild and gradual increase in systolic pressure over a period of 4 weeks (113 +/- 1 vs. 137 +/- 3 mm Hg) and was associated with an increase in the in vivo formation of prostaglandins I2 and E2 and of thromboxane A2 in the kidney. High sodium intake induced a fall in the urinary levels of prostaglandin E2 and a rise in the arterial pressure of control rats (126 +/- 1 vs. 113 +/- 1 mm Hg) but did not influence aldosterone-induced hypertension. Indomethacin (3.0 mg/kg/day) caused a profound inhibition of the in vivo synthesis of prostaglandin I2 and thromboxane A2 without modifying the renal production of prostaglandin E2. Although indomethacin exerted no effect on aldosterone-induced hypertension in rats fed a normal diet, it caused a further rise in systolic pressure in aldosterone-treated rats fed a high sodium diet (157 +/- 6 vs. 140 +/- 4 mm Hg). The results of this study in a model of aldosterone-induced mild hypertension in the rat indicate that 1) aldosterone exerts a stimulatory effect on the renal synthesis of prostanoid, particularly prostaglandin E2; 2) thromboxane A2 and prostaglandin I2 do not seem to play a role in aldosterone-induced hypertension under conditions of normal dietary salt intake, whereas the role of prostaglandin E2 is unclear; 3) there is enough sodium in a normal diet to allow for the maximal expression of the hypertensive effect of aldosterone; 4) prostaglandin I2 seems to play a significant role in modulating the cardiovascular impact of a high sodium diet in aldosterone-treated rats; and 5) the renal biosynthesis of prostaglandin E2 is particularly resistant to the inhibitory effect of indomethacin in vivo.

Comodulation masking release for a 700-Hz pure-tone signal was investigated as a function of the number and spectral positions of 20-Hz-wide comodulated flanking bands. In the first experiment, all stimuli were presented diotically. CMR was examined as a function of the number of flanking bands present, in conditions where the bands were arranged symmetrically around the signal frequency, were below the signal frequency, or were above the signal frequency. The number of flanking bands ranged from one to eight, and the magnitude of the diotic CMR ranged from approximately 5-16 dB. The results indicated: (1) bands closer to the signal resulted in larger masking release, and (2) more bands gave rise to larger CMR (but with diminishing returns above two flanking bands). Two additional sets of diotic conditions were examined and compared to the condition where all eight comodulated flanking bands were present: In one set of conditions, two of the eight flanking bands were removed; in the other set of conditions, two of the eight flanking bands were replaced with bands (termed "deviant" bands) that were not comodulated with respect to the other bands. There was very little effect of reducing eight bands to six, even when the removed bands were relatively near the signal frequency; however, CMR was substantially reduced when deviant bands were introduced, particularly when the deviant bands were placed relatively near the signal frequency. These reductions in CMR were slightly greater when each of the deviant bands had a unique modulation pattern (bideviant bands) than when the two deviant bands themselves shared the same modulation pattern (codeviant bands). In the second experiment, dichotic conditions were examined where the number and spectral positions of the flanking bands in the nonsignal ear were varied (the signal ear received only a 20-Hz-wide noise band centered on the signal frequency). The magnitude of the dichotic CMR ranged from approximately 2-10 dB, depending on condition. Effects of proximity and the number of flanking bands were similar to the effects obtained in diotic conditions. For both the diotic and the dichotic data, the effects of proximity were more consistent with an interpretation based upon across-channel processing than upon a within-channel interaction. The results obtained using deviant bands indicate that it is difficult for the auditory system to disregard the modulation pattern of flanking bands that differ from the modulation pattern of the on-signal band, particularly if such bands are proximal to the signal frequency.

A small number of blood transfusions (1-3) seems sufficient to improve the cadaveric renal allograft outcome, probably via induction of some nonspecific suppressive activity. This activity was assessed by the concanavalin A (Con A) enhancement method; when present, the response of freshly isolated patients' cells to a submitogenic dose of Con A was lowered, leading to a Con A ratio greater than 5, significantly (P less than 0.0001) higher than the one observed in normal controls or untransfused uremic patients. The correlation between this suppressive activity and graft outcome was determined. Thirty-five patients were studied over a 12-month period for graft function (creatinine level) and survival. Both parameters were significantly improved in the group of patients whose Con A ratio was greater than 5 after transfusions. A soluble suppressor factor, or factors, released into the supernatant of patients' lymphocytes cultured for 48 hr, seems responsible for this suppressive activity. Moreover this process is nonspecific, since it suppresses mitogenic response of cells isolated from normal untransfused volunteers, and could be observed when peripheral blood mononuclear cells were used, but not with purified adherent or nonadherent cells. Addition of indomethacin to the cells during the elaboration of the supernatant abolished this activity. However, amounts of PGE2 secreted into the supernatant during the 48 hr of culture could not be correlated with this suppressive activity. These findings suggest that induction of nonspecific immunosuppression by a few blood transfusions could predict a better kidney graft outcome.

1. Urinary excretion rate of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), a stable nonenzymatic transformation product of prostacyclin (PGI2), was measured in 13 patients with sustained essential hypertension and in nine normotensive control subjects by a specific radioimmunoassay. 2. Patients with essential hypertension had significantly lower 6-keto-PGF1 alpha excretion rates irrespective of their sex, but in both groups urinary 6-keto-PGF1 alpha was lower in females. 3. Sodium excretion was significantly correlated with urinary 6-keto-PGF1 alpha only in hypertensive subjects. There was also a positive correlation between 6-keto-PGF1 alpha and urine volume in control subjects and in hypertensive patients. 4. If diminished urinary 6-keto-PGF1 alpha reflects suppressed endogenous PGI2 production, a deficiency in this important vasodepressor substance in essential hypertension may contribute to the pathogenesis of this disease.

Detection of signals composed of one, two, or three pure-tone components was examined in comodulated and noncomodulated masking noises. The masking noise was either a single 30-Hz-wide narrow band of noise, two narrow bands of noise, or three narrow bands of noise. Comodulation masking release (CMR) was greatest when (1) the signal was a single pure tone; (2) the masker was composed of three noise bands (as opposed to two); and (3) at least one flanking band was lower in frequency than the signal. Substantial CMRs did occur, however, for two- and three-component signals presented in two- and three-component maskers, respectively. The results of the present experiments did not support a "dip listening" hypothesis, nor models based strictly on across-frequency differences in stimulus envelope pattern or correlation. The results were more consistent with a model of CMR in which across-frequency envelope difference is coded by subtracting the envelope at the signal frequency from the envelope at a flanking frequency.

The detection of 500- or 2000-Hz pure-tone signals in unmodulated and modulated noise was investigated in normal-hearing and sensorineural hearing-impaired listeners, as a function of noise bandwidth. Square-wave modulation rates of 15 and 40 Hz were used in the modulated noise conditions. A notched noise measure of frequency selectivity and a gap detection measure of temporal resolution were also obtained on each subject. The modulated noise results indicated a masking release that increased as a function of increasing noise bandwidth, and as a function of decreasing modulation rate for both groups of listeners. However, the improvement of threshold with increasing modulated noise bandwidth was often greatly reduced among the sensorineural hearing-impaired listeners. It was hypothesized that the masking release in modulated noise may be due to several types of processes including across-critical band analysis (CMR), within-critical band analysis, and suppression. Within-band effects appeared to be especially large at the higher frequency region and lower modulation rate. In agreement with previous research, there was a significant correlation between frequency selectivity and masking release in modulated noise. At the 500-Hz region, masking release was correlated more highly with the filter skirt and tail measures than with the filter passband measure. At the 2000-Hz region, masking release was correlated more with the filter passband and skirt measures than with the filter tail measure. The correlation between gap detection and masking release was significant at the 40-Hz modulation rate, but not at the 15-Hz modulation rate. The results of this study suggest that masking release in modulated noise is limited by frequency selectivity at low modulation rates, and by both frequency selectivity and temporal resolution at high modulation rates. However, even when the present measures of frequency selectivity and temporal resolution are both taken into account, significant variance in masking release still remains unaccounted for.

Hematocrit, red blood cell mass, plasma volume and plasma renin activity were evaluated in 33 (15 women) young patients with borderline hypertension and in 30 (15 women) age- and sex-matched normotensive control subjects. Mean hematocrit values were slightly but significantly higher (P less than 0.05) at this early stage of hypertension and it correlated with the elevation of arterial hypertension (r = 0.39, P less than 0.05). Red blood cell mass was normal indicating normal bone marrow production. Plasma volume was significantly contracted (p less than 0.05) and it can account in part for the increased hematocrit and plasma renin activity. These results indicate that the alterations in circulating fluid components and in hematocrit described in moderate to severe forms of hypertension are also present in early borderline hypertension.

A reverse-phase isocratic HPLC method is described for direct simultaneous assay of ATP, ADP, AMP, S-adenosylmethionine, S-adenosylhomocysteine, S-adenosylethionine, and other adenine derivatives in liver microbiopsies. The procedure was tested in conditions which alter the hepatic content of adenine nucleotides and sulfur-adenosyl amino acids in humans, rats, and guinea pigs.

A study was undertaken in 19 patients with benign to moderate essential hypertension to verify the effect of indapamide alone or combined with a beta-blocker on plasma renin activity, plasma aldosterone, serum potassium and urinary prostaglandins PGE2 and PGF2a. Blood pressure was normalized in 11 (58%) patients with 2.5 mg indapamide/day. In the remaining 8 patients, the addition of pindolol resulted in blood pressure control. Under indapamide, a 70% increase in plasma renin activity and 81% (p less than 0.01) in plasma aldosterone was observed, whereas there was an 18% (p less than 0.001) decrease in potassium. Simultaneously, an increase in urinary PGE2 and PGF2a was observed; these values were significant for PGE2 (p less than 0.025). The addition of pindolol did not produce significant change in the biochemical parameters measured. The increase in the excretion rate of primary prostaglandins could play a role in the mode of action of indapamide.

The antihypertensive effects of labetalol infusion (2 mg/min; maximal dose 150 mg) were evaluated in 22 subjects requiring rapid lowering of blood pressure because of severe hypertension, a hypertensive crisis after surgery, or before angiographic examination. Overall systolic and diastolic blood pressures were reduced from 201 +/- 4 to 164 +/- 4 mm Hg and from 123 +/- 3 to 107 +/- 3 mm Hg, respectively. By the end of the infusion, diastolic blood pressure in 16 (73%) subjects was lowered to less than or equal to 110 mm Hg. No adverse effects were encountered, but one subject had a transitory hypotensive episode that did not require treatment. Intravenous labetalol appears effective and well tolerated in the control of blood pressure in hypertensive emergencies.

Gap detection was measured as a function of noise bandwidth with constant high-frequency cutoff in both normal-hearing and cochlear-impaired listeners. Band-widening functions were measured in a low-frequency region (0.6-kHz upper cutoff) and a high-frequency region (2.2-kHz upper cutoff). Measures of frequency selectivity were also obtained in the two frequency regions. The results for the normal-hearing listeners indicated that, on a double logarithmic scale, gap thresholds improved more steeply with increasing bandwidth in the higher frequency region than in the lower. However, performance at the narrow bandwidths was independent of frequency region. For the cochlear-impaired listeners, gap thresholds were generally longer than normal in both frequency regions. However, in the higher frequency region, progressively more listeners approached normal values as bandwidth was increased. The elevated gap thresholds were due in part to the higher absolute thresholds and in part to poor ability to process stimulus fluctuation. No correspondence was found between gap detection performance and frequency selectivity.