Sharon M. Abel

Duration Discrimination of Noise and Tone Bursts

This research investigates the human observers ability to discriminate difference in duration for noise bursts and gated sinusoids. Two observers compared two durations T and T+ΔT in a two‐alternative forced‐choice procedure. The value of T ranged from 0.16 to 960 msec. For each T the value of ΔT for 75% discrimination was determined. The results showed that for most of the range investigated ΔT was proportional to T12. Performance was not affected by a change in bandwidth from 3500 to 200 Hz. Values of ΔT for 75% correct did decrease, however, when the observers were given audible spectral cues from very short pulsed sinusoids. The theory best describing the results was the neural counter model proposed by Creelman [J. Acoust. Soc. Amer. 34, 582–593 (1962)].

The effect of aging on horizontal plane sound localization

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.

Sound localization: effects of reverberation time, speaker array, stimulus frequency, and stimulus rise/decay.

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.

Speech intelligibility in noise: Effects of fluency and hearing protector type

This research investigated the effect of car protectors on the intelligibility of speech in noise. Listeners with normal hearing, high-frequency, and flat loss were tested. Half the subjects in each group were fluent in English and half-poorly conversant. Taped lists of 25 words were presented free field under conditions defined by the speech-to-noise ratio, spectrum of noise background, and presence of ear protection. The results showed that intelligibility decreased with speech-to-noise ratio and was poorer in crowd noise than in white noise. The protector had no effect for the normal listener, but caused a substantial decrement in those with impairment. In all groups nonfluency contributed an additional loss of 10% to 20%. Significant differences in performance were noted for different muff and plug types.

Effects of rise/decay time on the lateralization of interaurally delayed 1-kHz tones.

Experiments in lateralization were performed to evaluate the relative contribution of onset and phase cues in binaural hearing. A 1-kHz signal was presented with interaural stimulus delays ranging from 0 to 1000 microseconds, corresponding to phase shifts of 0 degree to 360 degrees. For a given value of delay, the leading signal was presented randomly to the right or left ear over a block of 100 trials, and the laterality of the resultant image was judged. The percentage of correct judgments was plotted as a function of delay with rise/decay time as a parameter. Values of rise/decay time ranged from 0 to 500 ms. The results indicated that rise/decay times of at least 200 ms are necessary to avoid contributions from the onset cue to the formation of lateralization judgments. For rise/decay times shorter than 200 ms, a conflict occurs between phase and onset cues in the region of phase shifts from 180 degrees to 360 degrees. At the limit with very short rise/decay times, the onset cue completely overrides the phase cue.

Lateralization based on interaural phase differences: Effects of frequency, amplitude, duration, and shape of rise/decay

Experiments in lateralization were performed to evaluate the relative contribution of envelope and phase cues in binaural hearing with particular reference to the effects of frequency, amplitude, shape of rise/decay, and duration of peak amplitude. Pure-tone signals were presented with interaural phase shifts ranging between 90 degrees and 360 degrees. For a given value of phase shift, the leading signal was presented randomly to the right or left ear over a block of 100 trials, and the laterality of the resultant image was judged. Rise/decay time was varied from 5 to 200 ms across blocks. The results confirmed our previous finding that a rise/decay time of at least 200 ms is required to secure a psychophysically steady-state signal. This value will, however, depend on the values chosen for the other signal parameters. Within limits, decreasing intensity could be compensated for by decreasing rise/decay, suggesting the psychophysical importance of the initial segment of the signal (precedence effect). For low frequencies of 650 to 1250 Hz, performance is sensitive to interaural phase shift and largely independent of frequency. For higher frequencies of 1500 and 2000 Hz, lateralization is independent of the phase cue and also largely insensitive to change in rise/decay time. Finally, performance remains unchanged with variation in peak duration ranging from 25 to 200 ms.

Person‐environment interaction as a determinant of labor length variables

A prospective study of 80 women, who elected home births, and 80, who chose hospital births, yielded information about combinations of psychological variables which predicted duration of the latent phase of labor, and total labor length. The results indicated that psychological factors influenced physiological outcomes in specific ways, depending upon the parturients parity and choice of birth setting. Anxiety variables predicted at least one of the two labor length variables in both the Home and Hospital Multigravida groups, and expectations of control predicted a labor length variable in both primigravidas and multigravidas giving birth at home. Arousal seeking tendency was a predictor of a labor length variable’ in all but Home Multigravidas, but the direction of the effect depended upon the chosen birth setting.

The role of high-frequency hearing in age-related speech understanding deficits.

An experiment was conducted to further explore the effect of ageing on speech understanding under degraded listening conditions. Two groups of subjects, aged 20-39 years and 50-75 years were tested. Measurements were made of hearing thresholds in each ear from 0.25-10 kHz, consonant discrimination in quiet and continuous speech spectrum noise (S/N = −10 dB) and monophonic and stereophonic frequency selectivity. Neither group would have been diagnosed as hearing-impaired. Nonetheless, the older group had significantly higher hearing thresholds, which increased systematically with frequency. Poorer consonant discrimination in noise was observed for the older group. This outcome was correlated with high-frequency thresholds, not with age. There was no between-group difference in stereophonic frequency selectivity, minimizing the possibility of age-related changes in central auditory processing. Monophonic frequency selectivity, an index of cochlear processing, was correlated with speech understanding. The results support the conclusion that observed age-related effects are secondary to cochlear dysfunction.

The effect of the audallion BEAMformer noise reduction preprocessor on sound localization for cochlear implant users.

Objective To assess the effect of the Audallion ® BEAMformer noise reduction preprocessor on the sound localization ability of children fitted unilaterally with the Nucleus 22-channel cochlear implant. Design Eight children aged 11 to 14 yr participated. Using three arrays of six loudspeakers, each child was tested in a semi-reverberant sound proof booth representative of a small office environment. The six loudspeakers were positioned 30° apart in the horizontal plane at a distance of 1 m, spanning 150° either directly in front of or to the left or right of the subject. The stimulus to be localized was a 300 msec broadband noise with a rise/decay of 50 msec. Subjects were tested with the BEAMformer in four possible settings, including one single microphone control condition, with each of the three loudspeaker arrays. One block of 60 forced-choice speaker identification trials was presented for each of the 12 listening conditions. On each trial, the stimulus was emitted by one of the six loudspeakers, randomly selected. Results Results demonstrated that subjects were unable to discriminate among sound sources arrayed horizontally in space using the cochlear implant microphone alone, or in combination, with the BEAMformer microphone located on the other ear. Results also showed that using the BEAMformer did not bias the perception of spatial location. Conclusions The localization of acoustic stimuli in pediatric cochlear implant users was unaffected by the use of the Audallion® BEAMformer. The apparent origin of most sounds appears to be pulled toward the implanted ear. Further studies are needed to validate findings.

The use of a Temporary Extracochlear Electrode in Preoperative Testing of Permanent Implant Candidates

This paper describes hearing and speech perception in 9 post-lingually deaf adults fitted with a temporary single electrode, surgically positioned close to the round window niche. After baseline testing, unaided and aided binaurally with the high-power Phonic Ear PE 845, each subject was admitted to hospital for a period of 7 days. During each test session, stimuli were presented directly to the electrode lead by means of an isolation unit. Current thresholds, upper tolerable limits and gap detection were measured for various acoustical waveforms and stimulus frequencies. A laryngograph was used to test the discrimination of prelinguistic and suprasegmental speech features. The results indicated that the prosthesis could provide acoustic sensations of loudness, pitch and duration that changed with stimulus waveform, level of current and frequency, and a gap threshold less than 50 msec. Lipreading appeared to be a necessary adjunct for consonant discrimination.