Frequency selectivity in the modulation domain estimated using forward masking: Effects of masker modulation depth and masker-signal delay.

The threshold for detecting amplitude modulation (AM) of a sinusoidal or noise carrier is elevated when the signal AM is preceded by masker AM applied to the same carrier. This effect, called AM forward masking, shows selectivity in the AM domain, consistent with the existence of a modulation filter bank (MFB). In this paper we explore the effect of two factors that can influence AM forward masking, using an 8-kHz sinusoidal carrier and a range of masker AM frequencies, f, both below and above the signal AM frequency, f, of 40 Hz.

Forward masking of amplitude modulation across ears and its tuning in the modulation domain.

Frequency selectivity in the amplitude modulation (AM) domain has been demonstrated using both simultaneous AM masking and forward AM masking. This has been explained using the concept of a modulation filter bank (MFB). Here, we assessed whether the MFB occurs before or after the point of binaural interaction in the auditory pathway by using forward masking in the AM domain in an ipsilateral condition (masker AM and signal AM applied to the left ear with an unmodulated carrier in the right ear) and a contralateral condition (masker AM applied to the right ear and signal AM applied to the left ear).

Discrimination of the phase of amplitude modulation applied to different carriers: Effects of modulation rate and modulation depth for young and older subjects.

The discrimination of amplitude modulation (AM) from frequency modulation (FM) of a 1000-Hz carrier, with equally detectable AM and FM, is better for a 2-Hz than for a 10-Hz modulation rate. This might reflect greater sensitivity to temporal fine structure for low than for high rates. Alternatively, AM-FM discrimination may depend on comparing fluctuations in excitation level on the two sides of the excitation pattern, which are in phase for AM and out of phase for FM.

Effects of Age and Hearing Loss on the Discrimination of Amplitude and Frequency Modulation for 2- and 10-Hz Rates.

Detection of frequency modulation (FM) with rate = 10 Hz may depend on conversion of FM to amplitude modulation (AM) in the cochlea, while detection of 2-Hz FM may depend on the use of temporal fine structure (TFS) information. TFS processing may worsen with greater age and hearing loss while AM processing probably does not. A two-stage experiment was conducted to test these ideas while controlling for the effects of detection efficiency.

Envelope regularity discrimination.

The ability to discriminate irregular from regular amplitude modulation was assessed using the "envelope regularity discrimination" test. The amount of irregularity was parametrically varied and quantified by an "irregularity index." Normative data were gathered for young subjects with normal audiometric thresholds.

Senescent Changes in Sensitivity to Binaural Temporal Fine Structure.

Differences in the temporal fine structure (TFS) of sounds at the two ears are used for sound localization and for the perceptual analysis of complex auditory scenes. The ability to process this binaural TFS information is poorer for older than for younger participants, and this may contribute to age-related declines in the ability to understand speech in noisy situations. However, it is unclear how sensitivity to binaural TFS changes across the older age range.

Development of a method for determining binaural sensitivity to temporal fine structure.

Objective: To develop and evaluate a test of the ability to process binaural temporal-fine-structure (TFS) information. The test was intended to provide a graded measure of TFS sensitivity for all listeners.

Design: Sensitivity to TFS was assessed at a sensation level of 30 dB using the established TFS-LF test at centre frequencies of 250, 500 and 750 Hz, and using the new TFS-AF test, in which the interaural phase difference (IPD) was fixed and the frequency was adaptively varied.

Preferred Compression Speed for Speech and Music and Its Relationship to Sensitivity to Temporal Fine Structure.

Multichannel amplitude compression is widely used in hearing aids. The preferred compression speed varies across individuals. Moore (2008) suggested that reduced sensitivity to temporal fine structure (TFS) may be associated with preference for slow compression.

Comparison of the CAM2A and NAL-NL2 hearing-aid fitting methods for participants with a wide range of hearing losses.

Objective: To compare preferences for sounds processed via a simulated five-channel compression hearing aid fitted using CAM2A and NAL-NL2.

Design: Within a trial, the same segment of sound was presented twice, once with CAM2A settings and once with NAL-NL2 settings, in random order. The participant indicated which one was preferred and by how much.

Modulation masking within and across carriers for subjects with normal and impaired hearing.

The detection of amplitude modulation (AM) of a carrier can be impaired by additional (masker) AM applied to the same carrier (within-carrier modulation masking, MM) or to a different carrier (across-carrier MM). These two types of MM were compared for young normal-hearing and older hearing-impaired subjects. The signal was 4- or 16-Hz sinusoidal AM of a 4000-Hz carrier.

Comparison of the CAM2 and NAL-NL2 hearing aid fitting methods.

Objective: To compare preference judgments for sounds processed via a simulated five-channel compression hearing aid with gains and compression ratios selected according to two recently introduced fitting methods, CAMEQ2-HF (hereafter named CAM2) and NAL-NL2.

Design: There were 15 participants with sloping sensorineural hearing loss. They had mild losses, typical of people who might be candidates for wide-bandwidth hearing aids.

A version of the TEN Test for use with ER-3A insert earphones.

Objective: The aim of this study was to develop a version of the threshold-equalizing noise (TEN) test for the diagnosis of dead regions for use with Etymotic ER-3A insert earphones. The use of such earphones is helpful when testing clients with asymmetric hearing loss or clients whose ear canals tend to collapse under the pressure of supra-aural headphones. It can also be useful when ambient noise levels are problematic.

Implementation of two tests for measuring sensitivity to temporal fine structure.

Objective: To implement two methods for measuring sensitivity to temporal fine structure (TFS) for use in assessing effects of hearing loss and age that may not be apparent from the audiogram.

Design: The TFS1 test was described by Moore and Sek (2009). The task is to discriminate a harmonic complex tone from a tone in which all frequency components are shifted upwards by the same amount in Hz.

Effect of level on the discrimination of harmonic and frequency-shifted complex tones at high frequencies.

Moore and Sęk [J. Acoust. Soc.

Implementation of a fast method for measuring psychophysical tuning curves.

Objective: To implement a fast method for measuring psychophysical tuning curves (PTCs) for use in clinical applications, such as assessment of frequency selectivity and detection of dead regions in the cochlea.

Design: The method is based on that described by Sek et al (2005) and has been implemented in software that can be run on a PC with a good-quality sound card. In addition to the main narrowband noise masker, a lowpass noise masker can be generated to prevent detection of a distortion band corresponding to the simple difference tone.

The origin of binaural interaction in the modulation domain.

The purpose of these experiments was to assess whether the detection of diotic 5 Hz "probe" modulation of a 4000 Hz sinusoidal carrier was influenced by binaural interaction of "masker" modulators presented separately to each ear and applied to the same carrier. A 50 Hz masker modulator was applied to one ear and the masker modulator applied to the other ear had a frequency of 55 or 27.5 Hz.

Polish sentence tests for measuring the intelligibility of speech in interfering noise.

The aim of this study was to develop Polish sentence tests for accurate measuring of speech intelligibility in masking interfering noise. Two sets of sentence lists have been developed. The first set was composed of 25 lists and was used for sentence intelligibility scoring.

Sensitivity of the human auditory system to temporal fine structure at high frequencies.

The frequency of sounds is coded partly by phase locking to the temporal fine structure (TFS) of the waveform evoked on the basilar membrane. On the basis of data obtained using sinusoids, it is usually assumed that in mammals, including humans, TFS information becomes unusable for frequencies above about 5000 Hz. Here, sensitivity to the TFS of complex sounds up to much higher frequencies is demonstrated.

Estimation of the center frequency of the highest modulation filter.

For high-frequency sinusoidal carriers, the threshold for detecting sinusoidal amplitude modulation increases when the signal modulation frequency increases above about 120 Hz. Using the concept of a modulation filter bank, this effect might be explained by (1) a decreasing sensitivity or greater internal noise for modulation filters with center frequencies above 120 Hz; and (2) a limited span of center frequencies of the modulation filters, the top filter being tuned to about 120 Hz. The second possibility was tested by measuring modulation masking in forward masking using an 8 kHz sinusoidal carrier.

Development of a fast method for determining sensitivity to temporal fine structure.

Recent evidence suggests that sensitivity to the temporal fine structure (TFS) of sounds is adversely affected by cochlear hearing loss. This may partly explain the difficulties experienced by people with cochlear hearing loss in understanding speech when background sounds, especially fluctuating backgrounds, are present. We describe a test for assessing sensitivity to TFS.

Perception of amplitude modulation by hearing-impaired listeners: the audibility of component modulation and detection of phase change in three-component modulators.

Two experiments were conducted to assess whether hearing-impaired listeners have a reduced ability to process suprathreshold complex patterns of modulation applied to a 4-kHz sinusoidal carrier. Experiment 1 examined the ability to "hear out" the modulation frequency of the central component of a three-component modulator, using the method described by Sek and Moore [J. Acoust.

Development of a fast method for determining psychophysical tuning curves.

Psychophysical tuning curves (PTCs) can be used to assess the frequency selectivity of the auditory system and to detect and delimit "dead regions" in the cochlea. However, the traditional method for determining PTCs takes too long for use in clinical practice. We evaluated a fast method for determining PTCs, using a band of noise that sweeps in centre frequency and a Békésy method to adjust the masker level required for threshold.

Estimation of the level and phase of the simple distortion tone the modulation domain.

These experiments were designed to test the idea that nonlinearities in the auditory system can introduce a distortion component into the internal representation of the envelope of a sound, and to estimate the phase of the hypothetical distortion component. In experiment 1, a two-alternative forced-choice (2AFC) task with feedback was used to measure psychometric functions for detecting 5-Hz probe modulation of a 4-kHz sinusoidal carrier in the presence of a masker modulator with components at 50 and 55 Hz (m=0.3 for each component).

Testing the concept of a modulation filter bank: the audibility of component modulation and detection of phase change in three-component modulators.

Two experiments were performed to test the concept that the auditory system contains a "modulation filter bank" (MFB). Experiment 1 examined the ability to "hear out" the modulation frequency of the central component of a three-component modulator applied to a 4-kHz sinusoidal carrier. On each trial, three modulated stimuli were presented.

Mechanisms of modulation gap detection.

It has been postulated that the central auditory system contains an array of modulation filters, each responsive to a different range of modulation frequencies present at the outputs of the (peripheral) auditory filters. In the present experiments, we tested what we call the "dip hypothesis," that a gap in modulation is detected using the "dip" in the output of the modulation filter tuned to the modulator frequency. In experiment 1, the task was to detect a gap in the sinusoidal amplitude modulation imposed on a 4-kHz carrier.