Effects of ethanol on synthesis of prostaglandin F2α in bovine females.

Ethanol stimulates the production of prostaglandins in many species. The purpose of this study was to verify the effect of ethanol on the production of prostaglandin F2α (PGF2α) and luteolysis in bovine females. In the first experiment, Holstein cows at day 17 of the oestrous cycle were treated with 100% ethanol (0.05 ml/kg of body weight, IV; n = 5), saline (0.05 ml/kg of body weight, IV; n = 4) or synthetic prostaglandin (150 µg of D-cloprostenol/cow, IM; n = 4). The plasma concentrations of 13, 14-dihydro-15-keto PGF2α (PGFM; the main metabolite of PGF2α measured in the peripheral blood) were assessed by radioimmunoassay (RIA). There was an acute release of PGFM in response to ethanol comparing to other treatments (p ≤ 0.05). However, only cows treated with PGF2α underwent luteolysis. In the second experiment, endometrial explants of cross-bred beef cows (n = 4) slaughtered at day 17 of the oestrous cycle were cultured for 4 h. During the last 3 h, the explants were cultured with medium supplemented with 0, 0.1, 1, 10 or 100 µl of 100% ethanol/ml. Medium samples were collected at hours 1 and 4 and concentrations of PGF2α were measured by RIA. Ethanol did not induce PGF2α production by the endometrium. In conclusion, ethanol does not cause luteolysis in cows because it stimulates production of PGF2α in extra-endometrial tissues.

Responses of auditory-nerve fibers to stimuli producing psychophysical enhancement.

A form of auditory "enhancement" can be demonstrated by omitting a component from a harmonic series for a few hundred milliseconds and then replacing it: the replaced component stands out perceptually. Psychophysical experiments have shown that components generate more forward masking when enhanced than when present but not enhanced. This result has been interpreted as demonstrating that enhancement involves an increase in gain in the frequency region of the replaced component. The present experiments sought physiological evidence of enhancement in the responses of auditory-nerve fibers in the guinea pig. In one condition a 200-Hz harmonic series lacking components near 2 kHz preceded another series with the 2-kHz component present (the "test" series). In this condition the mean discharge rate to the 2-kHz component was larger than the adapted responses to the other components of the test. In a second condition the test series was preceded by silence. In both conditions the 2-kHz component caused the same increase in firing rate. The average discharge rate sychronized to the 2-kHz component was also the same in both conditions. However, the proportion of the total discharge rate which was locked to 2 kHz was larger when the test followed the harmonic series than when it followed silence. Thus the contrast, in terms of both mean and synchronized rates, between the responses at 2 kHz and those at other frequencies, was increased when the test was preceded by the harmonic series. However, there was no evidence of an increase in gain (i.e., absolutely larger responses) in the 2-kHz region. It seems likely therefore that the mechanisms responsible for this aspect of auditory enhancement are located more central than the auditory nerve.

A comparison of the effectiveness of across-channel cues available in comodulation masking release and profile analysis tasks.

These experiments were designed to explore the benefit to signal detection of different types of across-channel cues, both alone and in combination. Some conditions were similar to those used in profile analysis (PA), and some to those used in comodulation masking release (CMR). Others were designed specifically to eliminate, or render unreliable, a particular across-channel cue so that the benefit to performance from another cue could be assessed. Thresholds for detecting an increment in level of a sinusoid, or of the carrier of a sinusoidally amplitude modulated (SAM) sinusoid, were measured in the presence or absence of four sinusoids or SAM sinusoids (flankers), two centered above and two centered below the signal frequency. The flankers were always modulated with the same depth as the target component during nonsignal intervals. The flankers, when present, were either equal in level to the nonsignal target sinusoid, or were scrambled in level (different in level both from each other and from the target by an amount that varied randomly from one stimulus to the next). In some conditions the overall level of the stimuli was also varied randomly from one stimulus to the next. The results indicate that about 5-6 dB of benefit arises from the cue of a disparity in level across frequency (a PA-type cue), and about 1-3 dB from the cue of a disparity in envelope modulation depth across frequency (a CMR-type cue). For some subjects, slightly less benefit occurred when the flankers were presented to the opposite ear as the signal, requiring across-ear comparisons. Scrambling the level of the flankers often impaired performance, especially when the overall level of the stimuli was fixed. This appears to reflect an across-channel interference effect.

Profile analysis and comodulation detection differences using narrow bands of noise and their relation to comodulation masking release.

Experiment 1 examined the ability to compare relative level across frequency (profile analysis) for stimuli that were dynamically varying over time. The task was to detect an increment in level of a narrow band of noise (the target) in the presence or absence (reference condition) of four flanking bands (FBs). The envelopes of the FBs were either the same as that of the target (correlated condition), independent of that of the target but the same as each other (co-uncorrelated condition), or all independent (all-uncorrelated condition). The overall level of the stimuli was either fixed or randomly varied from one stimulus to the next. The results showed that subjects can make effective use of spectral-shape cues even for stimuli whose amplitudes vary markedly over time. In the correlated condition, the threshold for detecting an increment in the level of the target band was decreased (relative to the reference condition) both when the overall level was fixed and when it was varied randomly from stimulus to stimulus. In the uncorrelated conditions, the FBs did not lead to better performance when the overall level was fixed; rather they produced a small interference effect. When the overall level was randomized, the presence of uncorrelated FBs produced thresholds that decreased with increasing bandwidth and, for a bandwidth of 64 Hz, produced an improvement in performance (relative to the reference condition) that was almost as large as that produced by the correlated FBs. It seems that the more rapid fluctuations in the wider bands of noise were smoothed by the auditory system, enabling information about the long-term spectral shape to be extracted effectively. Experiment 2 used similar stimuli, but the task was to detect the target, rather than to discriminate its level. Detection thresholds in the presence of FBs were lowest in the co-uncorrelated condition, higher in the correlated condition, and highest in the all-uncorrelated condition. Thus the presence of correlated FBs improved discrimination thresholds in the profile analysis task, but impaired performance in the detection task. Reasons for the discrepancy between the effects of correlated FBs in the two tasks are discussed in the context of the cues available to the listener.

Comodulation masking release as a function of type of signal, gated or continuous masking, monaural or dichotic presentation of flanking bands, and center frequency.

Thresholds were measured for detecting a signal centered in a narrow-band noise (NBN) masker (on-frequency band, OFB), for the OFB alone, and with two flanking bands (FBs) added to the OFB, one centered above and one below the OFB. The FBs were either correlated with the OFB or were independent and were presented either to the same ear as the signal plus OFB (monaural condition) or to the opposite ear (dichotic condition). The OFB and FBs were either gated with the signal, or were presented continuously. Three signal types were used: a pure tone; an NBN uncorrelated with the OFB; and an NBN correlated with the OFB. The signal was centered at 0.5, 2, or 6 kHz. Comodulation masking release was estimated either as the difference between threshold with the OFB alone and with the OFB plus correlated FBs [CMR(R-C)], or as the difference between thresholds using correlated and uncorrelated FBs [CMR(U-C)]. Although there were marked individual differences, positive CMR(R-C) values were found in all conditions for all three signal types. CMR(U-C) values were often larger than those for CMR(R-C), reflecting the fact that the uncorrelated FBs tended to produce interference effects, especially for the gated maskers, and at 6 kHz. Values of CMR were larger and more consistent across subjects for continuous than for gated maskers. For continuous maskers, the values of CMR tended to be smallest for the correlated-NBN signal. Results are discussed in terms of available cues and in terms of perceptual grouping mechanisms.

The processing of envelope information in comodulation masking release (CMR) and envelope discrimination.

In comodulation masking release (CMR), thresholds for a signal masked by a narrow-band noise are reduced when additional noise is present. To demonstrate CMR, the additional noise must have similar amplitude envelope fluctuations over time as the primary noise band masking the signal. The specific source of information that provides the reduction in masked threshold remains unclear, although it is the focus of recent interest. The envelope of the on-frequency masking band (OFB) changes with the addition of the signal at threshold: in the present work, the importance of these changes in providing the CMR has been investigated. First, CMR thresholds were collected in sinusoidally amplitude-modulated noises which varied either in the phase relationship of their envelopes or in their modulation depth. Then envelope discrimination (ED) thresholds were collected for changes in envelope phase disparity (i.e., envelope correlation) and for changes in modulation depth per se. The patterns of CMR thresholds with envelope phase disparity and with modulation depth are not similar to those of the ED thresholds. A computer simulation was conducted in which the stimulus waveforms were processed through an auditory model which comprised bandpass auditory filters, a square-law nonlinearity, and a sliding temporal window. The envelopes were then extracted from the processed waveforms to determine whether the envelope changes that occur in the signal intervals in the CMR and ED tasks may be similar. The results of this analysis indicate that discriminability of envelope correlation due to the addition of the signal at threshold in the CMR task was insufficient to explain CMR. However, the discriminability of changes in modulation depth due to the addition of the signal is in agreement with thresholds obtained from the CMR task.

Within- versus cross-channel mechanisms in detection of envelope phase disparity.

These experiments were designed to examine the mechanism of detection of phase disparity in the envelopes of two sinusoidally amplitude-modulated (AM) sinusoids. Specifically, they were performed to determine whether detection of envelope phase disparity was consistent with processing within a single channel in which the AM tones were simply added. In the first condition, with an 8-Hz modulation frequency, phase-disparity thresholds increased sharply with an initial increase in separation of the carrier frequencies. They then remained approximately constant when the separation was an octave or above. In the second condition, with carrier pairs of 1 and 2 kHz or 1 and 3.2 kHz and a modulation frequency of 8 Hz, thresholds were little affected as the level of one carrier was decreased relative to the other. With a modulation frequency of 128 Hz, for most subjects there was more of an effect of level disparity on thresholds. In the third condition, when the modulation frequency was 8 Hz, subjects showed relatively constant thresholds whether the signals were presented monotically, dichotically, or dichotically with low- and high-pass noise. Dichotic thresholds were typically higher than monotic when the modulation frequency was 128 Hz. These results suggest that it is not necessary to have information available within a single additive channel to detect envelope phase disparity. In certain circumstances, a comparison across channels may be used to detect such disparities.

Frequency discrimination near the spectral edge of simultaneous and forward maskers.

The effects of the presence of an amplitude discontinuity in the spectrum of a noise masker on frequency discrimination performance were examined. First, detection thresholds as a function of masker level were obtained for pure-tone signals masked by either simultaneous or forward white and low-pass maskers. Then frequency discrimination thresholds were obtained using four masker levels that were chosen to yield predetermined masked thresholds, with signal levels corresponding to each of three sensation levels above these masked thresholds. The principal results indicate that frequency discrimination is poorer in simultaneous low-pass noise than in simultaneous white noise, and that this difference in performance increases with increasing sensation level and with increasing masker level. These results are inconsistent with an explanation based on the pitches generated at spectral edges ("edge pitch"), pitch shifts, or disruption of phase-locking information, but are generally consistent with an explanation based on lateral suppression. It is proposed that a release from suppression may occur in filtered noise backgrounds at high noise levels and at high sensation levels. The reduced suppression may result in poorer frequency discrimination due, in part, to reduced signal detectability.

An investigation of the facilitation of simple auditory reaction time by predictable background stimuli.

Two experiments explored a surprising result reported by Emmerich, Pitchford, and Becker (1976): Simple reaction time (RT) to an auditory stimulus can be facilitated by the presence of a tonal background (or masker). In the first experiment, simple RT to a tonal signal was investigated for a variety of background frequencies and loudness levels, and significant facilitation of RT was found for low levels of the background. In the second experiment, no evidence of facilitation was found when the background stimulus was a randomly varying narrow-band noise, although evidence for facilitation was again found with a constant tonal background.

The relation between loudness and intensity difference limens for tones in quiet and noise backgrounds.

Recent studies of the relation between loudness and intensity difference limens (DLs) suggest that, if two tones of the same frequency are equally loud, they will have equal relative DLs [R. S. Schlauch and C.C. Wier, J. Speech Hear. Res. 30, 13-20 (1987); J.J. Zwislocki and H.N. Jordan, J. Acoust. Soc. Am. 79, 772-780 (1986)]. To test this hypothesis, loudness matches and intensity DLs for a 1000-Hz pure tone in quiet and in a 40-dB SPL spectrum level broadband noise were obtained for four subjects with normal hearing. The DLs were obtained in both gated- and continuous-pedestal conditions. Contrary to previous reports, equally loud tones do not yield equal relative DLs at several midintensities in the gated condition and at many intensities in the continuous condition. While the equal-loudness, equal-relative-DL hypothesis is not supported by the data, the relation between loudness and intensity discrimination appears to be well described by a model reported by Houtsma et al. [J. Acoust. Soc. Am. 68, 807-813 (1980)].

Edge effects on frequency discrimination of tones presented in low- and high-pass noise backgrounds.

Previous research has indicated that frequency discrimination performance is poorer for tones presented near the sharp spectral edge of a low-pass noise than for tones presented near the edge of a high-pass noise, or for tones in the same low-pass noise with high-pass noise added [Emmerich et al., J. Acoust. Soc. Am. 80, 1668-1672 (1986)]. The present study extends these findings in order to investigate how the steepness of the spectral edges of low- and high-pass maskers influences the discriminability of tones presented near these edges. Frequency discrimination was measured in each of three high- and low-pass noise backgrounds (which differed in the steepness of their filter skirts). The following results were obtained: (1) In the low-pass noise background, frequency discrimination performance improved as the filter skirt became more gradual; (2) in the high-pass noise background, performance first improved and then became poorer as the filter skirt became shallower; and (3) performance in low-pass noise was poorer than that in high-pass noise for the two steepest slopes employed (96 and 72 dB/oct) but not for the shallower slope (36 dB/oct). Results are discussed in the context of lateral suppression and edge pitch effects, and of a trade-off between possible edge effects and masking.

Frequency discrimination of tones presented in filtered noise.

Previous research (Emmerich et al., 1983) in which tones were presented in the center of the notches in band-reject noise backgrounds suggests that information from frequency regions remote from the nominal signal frequency is useful in frequency discrimination. The present work extends the earlier findings by presenting tones on either side of a notch so that only one (or the other) tail of the excitation patterns of the tones would fall into the notch. In addition, tones were presented in high-pass noise, low-pass noise, and various combinations of the two. The results again indicate that remote information affects frequency discrimination, and they are also consistent with the hypothesis that the low-frequency tail of the excitation pattern is more useful for frequency discrimination than is the high-frequency tail.

Frequency discrimination and signal detection in band-reject noise.

An experiment was conducted in order to compare the importance of information from frequency regions remote from the nominal signal frequencies for frequency discrimination and signal detection. In both tasks, signals were presented within the "notch" of band-reject noise, and different notch widths were employed. The results indicate that information is integrated over a wider range in frequency discrimination than in signal detection. Further, experiments in which a noise floor was present as well as band-reject noise, indicate that disrupting the information from regions remote from the nominal signal frequencies impairs frequency discrimination even in the absence of any significant impairment of signal detection performance.