A software package with a modular architecture has been developed to support perceptual modeling of the fine-grain spectro-temporal information observed in the auditory nerve. The package contains both functional and physiological modules to simulate auditory spectral analysis, neural encoding, and temporal integration, including new forms of periodicity-sensitive temporal integration that generate stabilized auditory images. Combinations of the modules enable the user to approximate a wide variety of existing, time-domain, auditory models. Sequences of auditory images can be replayed to produce cartoons of auditory perceptions that illustrate the dynamic response of the auditory system to everyday sounds.

An experiment was conducted to determine the effect of aging on sound localization. Seven groups of 16 subjects, aged 10-81 years, were tested. Sound localization was assessed using six different arrays of four or eight loudspeakers that surrounded the subject in the horizontal plane, at a distance of 1 m. For two 4-speaker arrays, one loudspeaker was positioned in each spatial quadrant, on either side of the midline or the interaural axis, respectively. For four 8-speaker arrays, two loudspeakers were positioned in each quadrant, one close to the midline and the second separated from the first by 15 degrees, 30 degrees, 45 degrees, or 60 degrees. Three different 300-ms stimuli were localized: two one-third-octave noise bands, centered at 0.5 and 4 kHz, and broadband noise. The stimulus level (75 dB SPL) was well above hearing threshold for all subjects tested. Over the age range studied, percent-correct sound-source identification judgments decreased by 12%-15%. Performance decrements were apparent as early as the third decade of life. Broadband noise was easiest to localize (both binaural and spectral cues were available), and the 0.5-kHz noise band, the most difficult to localize (primarily interaural temporal difference cue available). Accuracy was relatively higher in front of than behind the head, and errors were largely front/back mirror image reversals. A left-sided superiority was evident until the fifth decade of life. The results support the conclusions that the processing of spectral information becomes progressively less efficient with aging, and is generally worse for sources on the right side of space.

The HINT provides an efficient and reliable method of assessing speech intelligibility in quiet and in noise by using an adaptive strategy to measure speech reception thresholds for sentences, thus avoiding ceiling and floor effects that plague traditional measures performed at fixed presentation levels A strong need for such a test within the Canadian Francophone population, led us to develop a French version of the HINT. Here we describe the development of this test. The Canadian French version is composed of 240-recorded sentences, equated for intelligibility, and cast into 12 phonemically balanced 20-sentence lists. Average headphone SRTs, measured with 36 adult Canadian Francophone native speakers with normal hearing, were 16.4 dBA in quiet, -3.0 dBA SNR in a 65 dBA noise front condition and -11.4 dBA SNR in a 65 dBA noise side condition. Reliability was established by means of within-subjects standard deviation of repeated SRT measurements over different lists and yielded values of 2.2 and 1.1 dB for the quiet and noise conditions, respectively.

Correction factors can be used to predict performance on the HINT in a group of normal-hearing children in all HINT conditions, apart from quiet. Findings of the current study concur with the literature on age effects in auditory processing abilities, where performance on a variety of auditory tasks has been demonstrated to increase with age to reach adult-like values in adolescence or past 10 yrs.

This research assessed the ability of human listeners to localize one-third octave noise bands in the horizontal plane. The effects of reverberation time (absorbent versus reverberant room), stimulus center frequency (500, 1000, 2000, and 4000 Hz), stimulus rise/decay time (5 vs 200 ms) and speaker array (frontal versus lateral) were investigated for four subjects using a forced-choice speaker-identification paradigm. Sound localization scores were consistently lower in the reverberant room than in the absorbent room. They also revealed strong frequency and azimuthal effects. The benefit of a shorter rise/decay time was small and limited to low frequencies. The identification of a speaker position depended strongly upon the array in which it was embedded, primarily because localization in the lateral array led to frequency-dependent front/back confusions and response bias. The results also illustrated the importance of choosing a coordinate system based on the auditory cone-of-confusion to analyze localization data for speaker arrays spanning the aural axis.