Detection Of Sinusoidal Amplitude Modulation Research Articles

Basic auditory processing and emotion recognition in individuals at clinical high risk for psychosis

The ability to understand others' emotions from subtle cues is a critical skill for navigating the complex social world, with increasing demands placed on this capability as children enter adolescence. Individuals at clinical high-risk (CHR) of developing psychosis exhibit social isolation with specific impairments in social cognition (Thompson et al., 2011) and emotion recognition (Addington et al., 2008; Amminger et al., 2011; Corcoran et al., 2015). The degree of social impairment and the severity of emotion recognition deficits are greater in individuals who later convert to psychosis than in those who do not (Cornblatt et al., 2011). Emotion recognition deficits thus represent promising targets for improving early identification and intervention strategies (Addington et al., 2008; Amminger et al., 2011; Cornblatt et al., 2011; Kee et al., 2003; Niemi et al., 2005). A significant challenge remains however, to identify a precursor of emotional recognition deficits for use as a salient diagnostic tool and therapeutic target. Impairments in basic auditory processes may underlie the auditory emotion identification deficits and social functioning deficits associated with psychotic disorders and at-risk states. The auditory properties of speech convey emotional content (Banse and Scherer, 1996; Hammerschmidt and Jurgens, 2007), and the ability to identify emotion from these vocal cues is impaired in schizophrenia (Addington et al., 2008; Amminger et al., 2011; Bach et al., 2009; Corcoran et al., 2015; Cornblatt et al., 2011; Dickey et al., 2010; Dickey et al., 2008; Kee et al., 2003; Leitman et al., 2007; Leitman et al., 2010; Niemi et al., 2005; Thompson et al., 2011), schizotypal personality disorder (Dickey et al., 2010; Dickey et al., 2008), and CHR subjects (Corcoran et al., 2015; Thompson et al., 2011). We recently reported that individuals with schizophrenia exhibit wide ranging basic auditory processing deficits, and that additional basic auditory processing abilities, including formant discrimination, sinusoidal amplitude modulation detection, and duration discrimination are associated with the ability to recognize emotion in voice (Kraus et al., 2019). In this study, we have aimed to determine whether CHR individuals exhibit similar widespread auditory processing deficits associated with impaired emotion recognition.

A new measure of authentic auditory emotion recognition: Application to patients with schizophrenia

BackgroundMany social processes such as emotion recognition are severely impaired in patients with schizophrenia. While basic auditory processing seems to play a key role in identifying emotions, research in this field is limited due to the lack of proper assessment batteries. Many of the widely accepted tests utilize actors to portray certain emotions—these batteries are less ecologically and face valid. MethodsThis study utilized a newly developed auditory emotion recognition test that contained natural stimuli from spontaneous displays of emotions to assess 28 patients with schizophrenia and 16 healthy controls. ResultsThe results indicate that the newly developed test, referred to as the INTONATION Test, is more sensitive to the emotion recognition deficits in patients with schizophrenia than previously used measures. The correlations of the INTONATION Test measures with basic auditory processes were similar to established tests of auditory emotion. Particular emotion sub scores from the INTONTATION test, such as happiness, demonstrated the strongest correlations with specific auditory processing skills, such as formant discrimination and sinusoidal amplitude modulation detection (SAM60). ConclusionsThe results from this study indicate that auditory emotion recognition impairments are more pronounced in patients with schizophrenia when perceiving authentic displays of emotion. Understanding these deficits could help specify the nature of auditory emotion recognition deficits in patients with schizophrenia and those at risk.

Effects of age and noise exposure on the representation of amplitude modulation

Age and lifetime noise exposure were used as predictors for electrophysiological and psychophysical measures of amplitude modulation processing. Frequency-following responses (FFRs) were recorded from 61 listeners (20 young, 23 middle-aged, 18 elderly) to 0.6- and 2-kHz, 75-dB SPL, carrier tones amplitude modulated at 100 Hz. A pink noise highpass-filtered at 3 kHz was included to mask basal cochlear contributions to the FFR. Sinusoidal amplitude modulation detection (AMD) thresholds were measured for the same listeners for a 2-kHz carrier (40 and 80 dB SPL) and for three modulation frequencies (25, 50, and 100 Hz). The carrier was presented in notched pink noise to limit off-frequency listening. Lifetime noise exposure was estimated using a structured interview. A regression model was used to determine the independent contributions of age and noise exposure, while controlling for audiometric threshold. FFR amplitude for the 0.6 kHz carrier showed a marked age-related decline. Age was also associated with a significant increase in AMD thresholds. Lifetime noise exposure was not significantly associated with either FFR amplitude or AMD threshold. The results suggest that age is a stronger predictor of modulation processing deficits than lifetime noise exposure.

Depth matters - Towards finding an objective neurophysiological measure of behavioral amplitude modulation detection based on neural threshold determination

With increasing numbers undergoing intervention for hearing impairment at a young age, the clinical need for objective assessment tools of auditory discrimination abilities is growing. Amplitude modulation (AM) sensitivity has been known to be an important factor for speech recognition particularly among cochlear implant (CI) users. It therefore would be useful to develop objective measures of AM detection for future clinical assessment of CI users; this study aimed to verify the feasibility of a neurophysiological approach studying a cohort of normal-hearing participants. The mismatch waveform (MMW) was evaluated as a potential objective measure of AM detection for a low modulation rate (8 Hz). This study also explored the relationship between behavioral AM detection and speech-in-noise recognition. The following measures were obtained for 15 young adults with no known hearing impairment: (1) psychoacoustic sinusoidal AM detection ability for a modulation rate of 8 Hz; (2) neural AM detection thresholds estimated from morphology weighted cortical auditory evoked potentials elicited to various AM depths; and (3) AzBio sentence scores for speech-in-noise recognition. No significant correlations were found between speech recognition and behavioral AM detection measures. Individual neural thresholds were obtained from MMW data and showed significant positive correlations with behavioral AM detection thresholds. Neural thresholds estimated from morphology weighted MMWs provide a novel, objective approach for assessing low-rate AM detection. The findings of this study encourage the continued investigation of the MMW as a neural correlate of low-rate AM detection in larger normal-hearing cohorts and subsequently in clinical cohorts such as cochlear implant users.

Auditory and cognitive performance in elderly musicians and nonmusicians.

Musicians represent a model for examining brain and behavioral plasticity in terms of cognitive and auditory profile, but few studies have investigated whether elderly musicians have better auditory and cognitive abilities than nonmusicians. The aim of the present study was to examine whether being a professional musician attenuates the normal age-related changes in hearing and cognition. Elderly musicians still active in their profession were compared with nonmusicians on auditory performance (absolute threshold, frequency intensity, duration and spectral shape discrimination, gap and sinusoidal amplitude-modulation detection), and on simple (short-term memory) and more complex and higher-order (working memory [WM] and visuospatial abilities) cognitive tasks. The sample consisted of adults at least 65 years of age. The results showed that older musicians had similar absolute thresholds but better supra-threshold discrimination abilities than nonmusicians in four of the six auditory tasks administered. They also had a better WM performance, and stronger visuospatial abilities than nonmusicians. No differences were found between the two groups’ short-term memory. Frequency discrimination and gap detection for the auditory measures, and WM complex span tasks and one of the visuospatial tasks for the cognitive ones proved to be very good classifiers of the musicians. These findings suggest that life-long music training may be associated with enhanced auditory and cognitive performance, including complex cognitive skills, in advanced age. However, whether this music training represents a protective factor or not needs further investigation.

Separable developmental trajectories for the abilities to detect auditory amplitude and frequency modulation

Amplitude modulation (AM) and frequency modulation (FM) are inherent components of most natural sounds. The ability to detect these modulations, considered critical for normal auditory and speech perception, improves over the course of development. However, the extent to which the development of AM and FM detection skills follow different trajectories, and therefore can be attributed to the maturation of separate processes, remains unclear. Here we explored the relationship between the developmental trajectories for the detection of sinusoidal AM and FM in a cross-sectional design employing children aged 8–10 and 11–12 years and adults. For FM of tonal carriers, both average performance (mean) and performance consistency (within-listener standard deviation) were adult-like in the 8–10 y/o. In contrast, in the same listeners, average performance for AM of wideband noise carriers was still not adult-like in the 11–12 y/o, though performance consistency was already mature in the 8–10 y/o. Among the children there were no significant correlations for either measure between the degrees of maturity for AM and FM detection. These differences in developmental trajectory between the two modulation cues and between average detection thresholds and performance consistency suggest that at least partially distinct processes may underlie the development of AM and FM detection as well as the abilities to detect modulation and to do so consistently.

Detection of sinusoidal amplitude modulation in logarithmic frequency sweeps across wide regions of the spectrum

Many natural sounds such as speech contain concurrent amplitude and frequency modulation (AM and FM), with the FM components often in the form of directional frequency sweeps or glides. Most studies of modulation coding, however, have employed one modulation type in stationary carriers, and in cases where mixed-modulation sounds have been used, the FM component has typically been confined to an extremely narrow range within a critical band. The current study examined the ability to detect AM signals carried by broad logarithmic frequency sweeps using a 2-alternative forced-choice adaptive psychophysical design. AM-detection thresholds were measured as a function of signal modulation rate and carrier sweep frequency region. Thresholds for detection of AM in a sweep carrier ranged from −8 dB for an AM rate of 8 Hz to −30 dB at 128 Hz. Compared to thresholds obtained for stationary carriers (pure tones and filtered Gaussian noise), detection of AM carried by frequency sweeps substantially declined at low (12 dB at 8 Hz) but not high modulation rates. Several trends in the data, including sweep- versus stationary-carrier threshold patterns and effects of frequency region were predicted from a modulation filterbank model with an envelope-correlation decision statistic.

Enhanced discrimination of low-frequency sounds for subjects with high-frequency dead regions

Research using animals suggests that a lesion in the basal portion of the cochlea, causing a high-frequency 'dead region', leads to cortical reorganization, such that frequencies just below the edge frequency of the dead region, fe, become over-represented. We set out to determine if this reorganization has functional benefits. Two groups of subjects were tested, with and without acquired high-frequency dead regions, as assessed using the TEN(HL) test. For the ears with dead regions, the value of fe was close to 1000 or 1500 Hz. The two groups were matched in terms of audiometric thresholds for frequencies below fe and in terms of age. Three subjects with unilateral dead regions (with matched low-frequency audiometric thresholds across ears) were also tested. Three tasks were used: (i) frequency discrimination of sinusoidal tones. The level of every stimulus was roved over a 12-dB range to reduce the salience of loudness cues. The center frequencies used ranged from 250 Hz to just below fe; (ii) detection of sinusoidal amplitude modulation of a sinusoidal carrier. Carrier frequencies of 500 and 800 Hz were used with all subjects, and an additional carrier frequency of 1200 Hz was used for ears with fe close to 1500 Hz and their matched counterparts. Modulation frequencies were 4, 50 and 100 Hz; (iii) identification of consonants in nonsense syllables. The syllables were lowpass filtered at 1000 or 1500 Hz (depending on the value of fe) and complementary highpass-filtered noise was presented to prevent use of information from neurons tuned above fe. For the frequency-discrimination task, the ears with dead regions showed a significant local improvement ('enhanced' thresholds) for frequencies just below fe, as has been reported previously. For the subjects with unilateral dead regions, the enhancement occurred only for the ears with dead regions. For the amplitude-modulation detection task, thresholds were generally lower for the ears with dead regions than for the ears without, and this effect was statistically significant. For the subjects with unilateral dead regions, thresholds were lower for the ears with dead regions than for the ears without. Consonant identification was significantly better for the ears with than without dead regions, and this was true for the subjects with unilateral dead regions. We conclude that a dead region at high frequencies is associated with a better ability to process information at low frequencies. These effects may reflect cortical plasticity induced by the dead regions.

Comparison of level discrimination, increment detection, and comodulation masking release in the audio- and envelope-frequency domains.

In general, the temporal structure of stimuli must be considered to account for certain observations made in detection and masking experiments in the audio-frequency domain. Two such phenomena are (1) a heightened sensitivity to amplitude increments with a temporal fringe compared to gated level discrimination performance and (2) lower tone-in-noise detection thresholds using a modulated masker compared to those using an unmodulated masker. In the current study, translations of these two experiments were carried out to test the hypothesis that analogous cues might be used in the envelope-frequency domain. Pure-tone carrier amplitude-modulation (AM) depth-discrimination thresholds were found to be similar using both traditional gated stimuli and using a temporally modulated fringe for a fixed standard depth (ms = 0.25) and a range of AM frequencies (4-64 Hz). In a second experiment, masked sinusoidal AM detection thresholds were compared in conditions with and without slow and regular fluctuations imposed on the instantaneous masker AM depth. Release from masking was obtained only for very slow masker fluctuations (less than 2 Hz). A physiologically motivated model that effectively acts as a first-order envelope change detector accounted for several, but not all, of the key aspects of the data.

A perceptual learning investigation of the pitch elicited by amplitude-modulated noise

Noise that is amplitude modulated at rates ranging from 40 to 850 Hz can elicit a sensation of pitch. Here, the processing of this temporally based pitch was investigated using a perceptual-learning paradigm. Nine listeners were trained (1 hour per day for 6-8 days) to discriminate a standard rate of sinusoidal amplitude modulation (SAM) from a faster rate in a single condition (150 Hz SAM rate, 5 kHz low-pass carrier). All trained listeners improved significantly on that condition. These trained listeners subsequently showed no more improvement than nine untrained controls on pure-tone and rippled-noise discrimination with the same pitch, and on SAM-rate discrimination with a 30 Hz rate, although they did show some improvement with a 300 Hz rate. In addition, most trained, but not control, listeners were worse at detecting SAM at 150 Hz after, compared to before training. These results indicate that listeners can learn to improve their ability to discriminate SAM rate with multiple-hour training and that the mechanism that is modified by learning encodes (1) the pitch of SAM noise but not that of pure tones and rippled noise, (2) different SAM rates separately, and (3) differences in SAM rate more effectively than cues for SAM detection.

Temporal envelope perception in dyslexic children.

Speech intelligibility depends heavily on the accurate perception of auditory temporal envelope cues, that is the slower amplitude modulations present in the speech waveform. In a previous study, McAnally and Stein demonstrated that dyslexics may show impaired audibility (i.e. detectability) of these envelope cues. In the present psychophysical study, the ability to process temporal envelope cues was further investigated in dyslexic children by measuring detection thresholds of sinusoidal amplitude-modulation (SAM) and discrimination thresholds of SAM depth and SAM rate. Each threshold was measured at slow and fast SAM rates of 4 and 128 Hz, respectively. Overall, SAM thresholds were higher in dyslexics than in controls at both rates. The strongest deficit was observed at 4 Hz in the SAM detection task, but a deficit was also apparent at 128 Hz in the SAM discrimination tasks. Therefore, these results reveal that, in addition to reduced audibility of slow and fast envelope cues, some dyslexic children show poor encoding fidelity for these cues (as measured by the discrimination tasks). Overall, these findings are consistent with Tallal's hypothesis according to which the speech and reading deficits in some dyslexics may be caused by impaired temporal processes.

The influence of practice on the detectability of auditory sinusoidal amplitude modulation

The capacity to detect fluctuations in sound amplitude influences the perception of many everyday sounds, including speech. Here, the influence of practice on this ability was investigated. Between two testing sessions, one group of nine listeners who were tested on the detection of sinusoidal amplitude modulation (SAM) improved by about 0.7 dB on each of five conditions (300 trials/condition). Nine other listeners participated in these same sessions, but between them, practiced 4320 trials detecting the presence of 80-Hz SAM with a 3- to 4-kHz narrow-band carrier. Only three of these listeners, who had among the highest initial detection thresholds on the trained condition, improved during this training phase. These learners subsequently improved at untrained modulation rates (30 and 150 Hz) with the trained carrier, but not at the trained modulation rate with untrained carriers (0.5–1.5 kHz and 0–5 kHz). These data suggest that (1) at some stage, modulation processing is more linked to the carrier spectrum than to the modulation rate, and (2) while most normal-hearing listeners reach their best modulation-detection performance with minimal experience, listeners with high initial thresholds benefit from extended practice. Thus, training may aid populations that have difficulty detecting amplitude modulation. [Work supported by NIDCD.]

Detection of amplitude modulation and discrimination of interaural differences in modulation phase for high-frequency carriers

Using a 4-kHz pure-tone carrier and modulation frequencies (fm) of 2–512 Hz, thresholds for monaural detection of sinusoidal amplitude modulation (SAM) were measured, as were threshold modulation depths for the discrimination of interaurally in-phase and out-of-phase SAM envelopes. For one listener, interaural differences in envelope phase for fm up to 256 Hz were discriminable at modulation depths (m) for which the monaural modulation itself was just detectable, and all monaural and binaural thresholds were within a range of 5 dB (20 log m) across fm. For a second listener, binaural thresholds increased more rapidly with increasing fm than monaural thresholds. Another experiment examined the notion that interaurally delayed SAM envelopes are processed as time-varying interaural level differences. In this task, listeners discriminated interaurally in-phase SAM envelopes from SAM envelopes carrying a fixed interaural phase difference (IPD). Threshold m was measured for several fm and IPD combinations. For a given IPD, thresholds were either constant or decreased with increasing fm. The data suggest that dynamically varying interaural level differences are the cue to discrimination at low fm, while the fixed interaural time difference is the likely cue at high fm. [Work supported by NIDCD DC00683.]

Measurement of the Temporal-Modulation Transfer Function for a Single Listener with Cochlear Hearing Loss and Left-Hemisphere Damage

The modulation depth required for the detection of sinusoidal amplitude-modulation applied to a white noise carrier was measured as a function of modulation frequency, giving temporal modulation transfer functions (TMTFs). Five adult listeners with normal hearing (mean age 52 years), five elderly listeners with moderate cochlear hearing loss (mean age 66 years) and a single elderly listener (aged 73 years) with moderate cochlear hearing loss and left-hemisphere damage were tested in the right ear at 50 dB SL. The five elderly listeners were matched in audiogram with the brain-damaged listener. Modulation detection was systematically poorer than normal in the five elderly listeners with cochlear hearing loss. However, their TMTFs were lowpass in shape, as for the five normal-hearing adult listeners. Modulation detection was much poorer in the elderly listener with cochlear hearing loss and left-hemisphere damage compared to the five normal-hearing adults and the five elderly listeners with cochlear hearing loss. Moreover, modulation detection was poorer at 4, 64 and 128 Hz than at 8, 16 and 32 Hz in the brain-damaged listener, giving his TMTF a bandpass appearance. These results are in agreement with the hypothesis that the main factors limiting the ability to detect changes in the temporal-envelope of sounds are located at a central (retro-cochlear) level of the auditory system rather than at a peripheral (cochlear) level. They also suggest that the TMTF approach may prove useful in distinguishing peripheral and central hearing losses.

Auditory Temporal Envelope Processing in a Patient with Left-hemisphere Damage

Abstract Auditory temporal envelope processing was investigated in a patient showing a mild speech identification impairment following left-hemisphere damage. Three tasks evaluated the patient's ability to: (1) detect a sinusoidal amplitude modulation (SAM) applied to a white noise, as a function of modulation rate (i.e. her ‘temporal modulation transfer function’ or TMTF); (2) discriminate between two white noises amplitude modulated by time-reversed temporally asymmetric envelopes; and (3) identify white noises amplitude modulated by the temporal envelope of speech stimuli. Measurements of intensity discrimination thresholds were performed as a control task. Compared to normal data, the results obtained with the brain-damaged patient showed: (1) increased thresholds for the detection of SAM; (2) increased thresholds for the discrimination of temporal asymmetry; and (3) a deficit in the identification of speechenvelope noise stimuli. In contrast, intensity discrimination thresholds were within the normal range. Taken together, the results indicate a general impairment in auditory temporal acuity, which is now specified as a deficit in the coding of envelope rate and shape, and a deficit in the ability to use temporal envelope cues in speech processing. These results support the hypothesis that left-hemisphere damage is associated with an impairment in time analysis, which may cause, in turn, speech intelligibility disorders.

Auditory temporal envelope processing in a patient with left-hemisphere damage

Auditory temporal envelope processing was investigated in a patient showing a mild speech identification impairment following left-hemisphere damage. Three tasks evaluated the patient's ability to: (1) detect a sinusoidal amplitude modulation (SAM) applied to a white noise, as a function of modulation rate (i.e. her ‘temporal modulation transfer function’ or TMTF); (2) discriminate between two white noises amplitude modulated by time-reversed temporally asymmetric envelopes; and (3) identify white noises amplitude modulated by the temporal envelope of speech stimuli. Measurements of intensity discrimination thresholds were performed as a control task. Compared to normal data, the results obtained with the brain-damaged patient showed: (1) increased thresholds for the detection of SAM; (2) increased thresholds for the discrimination of temporal asymmetry; and (3) a deficit in the identification of speechenvelope noise stimuli. In contrast, intensity discrimination thresholds were within the normal range. Taken together, the results indicate a general impairment in auditory temporal acuity, which is now specified as a deficit in the coding of envelope rate and shape, and a deficit in the ability to use temporal envelope cues in speech processing. These results support the hypothesis that left-hemisphere damage is associated with an impairment in time analysis, which may cause, in turn, speech intelligibility disorders.

Detection of sinusoidal amplitude modulation at unexpected rates.

The detectability of sinusoidal amplitude modulation at unexpected modulation rates was assessed using a probe-signal method. With this method, three listeners were led to expect a target modulation rate (4, 32, or 256 Hz) by presenting the signal most often at that rate, and sensitivity to modulation at six other unexpected rates between 4 and 256 Hz was measured via occasionally presented probe modulation rates. The modulation phase was random on each two-interval forced-choice trial and the overall level of the 500-ms broadband carrier was randomly varied between 55 and 75 dB SPL across intervals. The modulation depth at each rate was set so that the modulation was detected on about 90% of the trials when only that rate was presented. Performance at the unexpected rates depended upon the target rate. For the 4-Hz target, modulation at all rates was detected on about 80% of the trials. For the 32- and 256-Hz targets, unexpected modulation rates of 16 Hz and above were detected on 80%-90% of the trials, but modulation rates below 16 Hz were detected nearly at chance. The influence of expectation of modulation rate on the detection of sinusoidal amplitude modulation is not readily predicted by current models of modulation detection.

The effects of frequency region and bandwidth on the temporal modulation transfer function.

Temporal resolution was examined as a function of frequency region and listening region. The first experiment demonstrated that amplitude- and frequency-modulated tones are not appropriate stimuli to study temporal resolution as a functional of frequency region, due to the availability of other cues in addition to temporal ones. In the other experiments, thresholds for detection of sinusoidal amplitude modulation of a noise band were measured as a function of frequency region, bandwidth, and level of surrounding notched noise masker. Temporal modulation transfer functions (TMTFs) measured in low- and high-frequency regions did not differ in sensitivity or in cutoff frequency, suggesting that initial "critical band" filtering did not affect temporal resolution. When the upper cutoff frequency of the noise was held constant, TMTF sensitivity increased with noise bandwidth, while the cutoff frequency of the TMTF did not show measurable change. These results are consistent with the predictions of an envelope detector model if peripheral filtering in the lower-frequency range is assumed to be approximately twice as wide as that estimated by measuring thresholds for a tone in notched noise. Restricting the listening region with notched noise increased thresholds for low modulation frequencies but not for high. This is consistent with other data showing that upward spread of excitation may increase the effective modulation depth, but only for low modulation frequencies.

Effects of modulator phase for comodulation masking release and modulation detection interference.

In an effort to evaluate the importance of across-frequency comparisons of envelope patterns in comodulation masking release (CMR) experiments and to compare joint effects of target-masker frequency separation for both CMR and modulation detection interference (MDI) tasks, thresholds were measured for three tasks. These tasks were: (a) the detection of sinusoidal amplitude modulation (SAM) of a tone, (b) the detection of a reduction in the modulation depth of a fully modulated SAM tone, and (c) the detection of a tone added to a narrow band of noise. Thresholds were obtained for the target alone and for the target presented with two maskers. For the detection of SAM, thresholds did not depend on whether the modulation patterns of the target and masker elements were the same or random. For the latter two tasks, modulator phase effects were apparent for target-masker frequency separations less than 1-2 oct. In contrast, past work has shown that observers can compare modulator envelope phases across frequency separations larger than 1-2 oct [Strickland et al., J. Acoust. Soc. Am. 86, 2160-2166 (1989); Yost and Sheft, J. Acoust. Soc. Am. 85, 848-857 (1989)]. In a second experiment, thresholds for the detection of SAM were obtained after prolonged exposure to a fully modulated SAM tone. For four of the five observers, modulation-rate specific adaptation was obtained for test/adapting carrier-frequency separations approaching 2 oct below and 1 oct above the adaptor.

Cues for discrimination of envelopes.

Thresholds for detection of sinusoidal amplitude modulation at a signal modulation frequency were measured in the presence of a masker modulation frequency, with broadband noise carriers. Broad tuning for modulation frequency was observed. For maskers half or twice the signal frequency, thresholds depended on the relative phases of the signal and masker. These results were used to determine what aspects of envelopes listeners might be using in making decisions. Simulations were performed using an envelope detector model, consisting of bandpass filtering, half-wave rectification, and low-pass filtering. Decisions were based on envelope statistics that have been used to predict other data. These statistics were (1) rms power, (2) ratio of maximum to minimum amplitude (max/min), (3) crest factor, (4) fourth moment, and (5) average slope. The max/min statistic was successful at predicting the major trends in the data, without requiring the presence of channels tuned to modulation frequency.