Age effects on discrimination of timing in auditory sequences

The experiments examined age-related changes in temporal sensitivity to increments in the interonset intervals (IOI) of components in tonal sequences. Discrimination was examined using reference sequences consisting of five 50-ms tones separated by silent intervals; tone frequencies were either fixed at 4 kHz or varied within a 2-4-kHz range to produce spectrally complex patterns. The tonal IOIs within the reference sequences were either equal (200 or 600 ms) or varied individually with an average value of 200 or 600 ms to produce temporally complex patterns. The difference limen (DL) for increments of IOI was measured. Comparison sequences featured either equal increments in all tonal IOIs or increments in a single target IOI, with the sequential location of the target changing randomly across trials. Four groups of younger and older adults with and without sensorineural hearing loss participated. Results indicated that DLs for uniform changes of sequence rate were smaller than DLs for single target intervals, with the largest DLs observed for single targets embedded within temporally complex sequences. Older listeners performed more poorly than younger listeners in all conditions, but the largest age-related differences were observed for temporally complex stimulus conditions. No systematic effects of hearing loss were observed.     

Age effects in discrimination of repeating sequence intervals

The study measured listener sensitivity to increments in the inter-onset intervals (IOIs) of successive 20-ms 4000-Hz tone bursts in isochronous sequences. The stimulus sequences contained two-six tone bursts, separated equally by silent intervals, with tonal IOIs ranging from 25 to 100 ms. Difference limens (DLs) for increments of the tonal IOIs were measured to assess listener sensitivity to changes of sequence rate. Comparative DLs were also measured for increments of a single interval located within six-tone isochronous sequences with different tone rates. Listeners included younger normal-hearing adults and two groups of older adults with and without high-frequency sensorineural hearing loss. The results, expressed as Weber fractions (DL/IOI), revealed that discrimination improved as the sequence tone rate decreased and the number of tonal components increased. Discrimination of a single sequence interval also improved as the number of sequence components increased from two to six but only for brief intervals and fast sequence rates. Discrimination performance of the older listeners with and without hearing loss was equivalent and significantly poorer than that of the younger listeners. The discrimination results are examined and discussed within the context of multiple-look mechanisms and possible age-related differences in the sensory coding of signal onsets.     

Age-related differences in discrimination of an interval separating onsets of successive tone bursts as a function of interval duration

The study measured listener sensitivity to increments in the inter-onset interval (IOI) separating pairs of successive 20-ms 4000-Hz tone pulses. A silent interval between the tone pulses was adjusted across conditions to create reference tonal IOI values of 25-600 ms. For each condition, a duration DL for increments of the tonal IOI was measured in listeners comprised of young normal-hearing adults and two groups of older adults with and without high-frequency hearing loss. Discrimination performance of all listeners was poorest for the shorter reference IOIs, and improved to stable levels for longer reference intervals exceeding about 200 ms. Temporal sensitivity of the young listeners was significantly better than that of the elderly listeners in each condition, with the largest age-related differences observed for the shortest reference interval. Age-related differences were also observed for duration DLs measured using single 4000-Hz tone bursts set to three reference durations in the range 50-200 ms. The tone DLs of all listeners were smaller than the corresponding tone-pair IOI DLs, particularly for the shorter reference stimulus durations. There were no significant performance differences observed between the older listeners with and without hearing loss for either discrimination task.     

Effects of age and sequence presentation rate on temporal order recognition

The experiments examined the ability of younger and older listeners to identify the temporal order of sounds presented in tonal sequences. The stimuli were three-tone sequences that spanned two-octave frequency range, and listeners identified random permutations of tone order using labels of relative pitch. Some of the sequences featured uniform timing characteristics, and the sequence duty cycle was varied across conditions to examine the relative influence of tonal durations and intertone interval on recognition performance across a range of sequence presentation rates. Other stimulus sequences featured nonuniform timing with unequal tone durations and intertone intervals. The listeners were groups of younger and older persons with or without hearing loss. Results indicated that temporal order recognition was influenced primarily by sequence presentation rate, independent of tonal duration, tonal interval spacing, or sequence timing characteristics. The performance of older listeners was poorer than younger listeners, but the age-related recognition differences were independent of sequence presentation rate. There were no consistent effects of hearing loss on temporal ordering performance.     

Intensity discrimination and increment detection in cochlear-implant users

Intensity difference limens (DLs) were measured in users of the Nucleus 22 and Clarion v1.2 cochlear implants and in normal-hearing listeners to better understand mechanisms of intensity discrimination in electric and acoustic hearing and to evaluate the possible role of neural adaptation. Intensity DLs were measured for three modes of presentation: gated (intensity increments gated synchronously with the pedestal), fringe (intensity increments delayed 250 or 650 ms relative to the onset of the pedestal), and continuous (intensity increments occur in the presence of a pedestal that is played throughout the experimental run). Stimuli for cochlear-implant listeners were trains of biphasic pulses; stimuli for normal-hearing listeners were a 1-kHz tone and a wideband noise. Clarion cochlear-implant listeners showed level-dependent effects of presentation mode. At low pedestal levels, gated thresholds were generally similar to thresholds obtained in the fringe and continuous conditions. At higher pedestal levels, however, the fringe and continuous conditions produced smaller intensity DLs than the gated condition, similar to the gated-continuous difference in intensity DLs observed in acoustic hearing. Nucleus cochlear-implant listeners did not show consistent threshold differences for the gated and fringe conditions, and were not tested in the continuous condition. It is not clear why a difference between gated and fringe thresholds occurred for the Clarion but not the Nucleus subjects. Normal-hearing listeners showed improved thresholds for the continuous condition relative to the gated condition, but the effect was larger for the 1-kHz tonal carrier than for the noise carrier. Findings suggest that adaptation occurring central to the inner hair cell synapse mediates the gated-continuous difference observed in Clarion cochlear-implant listeners and may also contribute to the gated-continuous difference in acoustic hearing.     

Temporal discrimination for single components of nonspeech auditory patterns

This paper extends previous research on listeners' abilities to discriminate the details of brief tonal components occurring within sequential auditory patterns (Watson et al., 1975, 1976). Specifically, the ability to discriminate increments in the duration delta t of tonal components was examined. Stimuli consisted of sequences of ten sinusoidal tones: a 40-ms test tone to which delta t was added, plus nine context tones with individual durations fixed at 40 ms or varying between 20 and 140 ms. The level of stimulus uncertainty was varied from high (any of 20 test tones occurring in any of nine factorial contexts), through medium (any of 20 test tones occurring in ten contexts), to minimal levels (one test tone occurring in a single context). The ability to discriminate delta t depended strongly on the level of stimulus uncertainty, and on the listener's experience with the tonal context. Asymptotic thresholds under minimal uncertainty approached 4-6 ms, or 15% of the duration of the test tones; under high uncertainty, they approached 40 ms, or 10% of the total duration of the tonal sequence. Initial thresholds exhibited by inexperienced listeners are two-to-four times greater than the asymptotic thresholds achieved after considerable training (20,000-30,000 trials). Isochronous sequences, with context tones of uniform, 40-ms duration, yield lower thresholds than those with components of varying duration. The frequency and temporal position of the test tones had only minor effects on temporal discrimination. It is proposed that a major determinant of the ability to discriminate the duration of components of sequential patterns is the listener's knowledge about "what to listen for and where." Reduced stimulus uncertainty and extensive practice increase the precision of this knowledge, and result in high-resolution discrimination performance. Increased uncertainty, limited practice, or both, would allow only discrimination of gross changes in the temporal or spectral structure of the sequential patterns.     

Duration discrimination of speech and tonal complex stimuli by normally hearing and hearing-impaired listeners

The ability to discriminate changes in the length of vowels and tonal complexes (filled intervals) and in the duration of closure in stop consonants and gaps in tonal complexes (unfilled intervals) was studied in three normally hearing and seven severely hearing-impaired listeners. The speech stimuli consisted of the vowels (i, I, u, U, a, A) and the consonants (p, t, k), and the tonal complexes consisted of digitally generated sinusoids at 0.5, 1, and 2 kHz. The signals were presented at conversational levels for each listener group, and a 3IFC adaptive procedure was used to estimate difference limens (DLs). The DLs for speech were similar to those for tonal complex stimuli in both the filled and unfilled conditions. Both normally and impaired-hearing listeners demonstrated greater acuity for changes in the duration of filled than unfilled intervals. Mean thresholds for filled intervals obtained from normally hearing listeners were smaller than those obtained from hearing-impaired listeners. For unfilled intervals, however, the difference between listener groups was not significant. A few hearing-impaired listeners demonstrated temporal acuity comparable to that of normally hearing listeners for several listening conditions. Implications of these results are discussed with regard to speech perception in normally and impaired-hearing individuals.     

Impacts of age on memory for auditory intensity

It is hypothesized that older listeners are more likely than younger listeners to be impaired when asked to make intensity judgments about target tones embedded in rapidly presented auditory sequences. This study examined this hypothesis by asking listeners ranging in age from 19 to 74?yr to make judgments of intensity based on narrowband noise bursts varying in frequency and intensity. In two experiments, listeners made intensity judgments of target bursts alone or embedded in sequences of bursts. In the first experiment, one of four fixed sequences was presented and had to be identified. In the second experiment, pre- or post-trial bursts acted as cues that identified the frequency of the target burst in the sequence. In both experiments, intensity discrimination thresholds for single bursts were good predictors of performance with sequences and were little affected by age. Significant negative relationships between age and accuracy were observed when single sequences had to be identified or a post-trial cue was used, but no age effects were apparent when a pre-trial cue was used. These data are interpreted as being consistent with previous suggestions that the aging process results in a decline in auditory memory capacity and/or internally generated selective attention.     

Learning to detect auditory pattern components

Listeners' abilities to learn to hear all the details of an initially unfamiliar sequence of ten 45-ms tones were studied by tracking detection thresholds for each tonal component over a prolonged period of training. After repeated listening to this sequence, the presence or absence of individual tones could be recognized, even though they were attenuated by 40-50 dB relative to the remainder of the pattern. Threshold-tracking histories suggest that listeners tend to employ two different learning strategies, one of which is considerably more efficient. Special training by reducing stimulus uncertainty and extending the duration of the target component was effective in increasing the rate of threshold improvement. Strategies acquired with the first pattern studied generalized to new sequences of tones. The possible implications of these results for the perceptual learning of speech or other auditory codes are discussed.     

Detection, loudness, and discrimination of five-component tonal complexes differing in crest factor

The detection, loudness, and discrimination performances of subjects with normal hearing were assessed using 3 five-component tonal complexes (1020-1100 Hz) with crest factors of 1.8, 2.6, and 3.2. The 3 five-component tonal complexes were: (1) equally detectable in broadband noise when presented at equal rms amplitude; (2) perceived as equally loud when presented at essentially equal rms amplitude; and (3) discriminable from one another when presented at equal loudness. The present data indicate that listeners can make discriminations on the basis of amplitude variations.     

Sound intensity processing by the goldfish

Capacities of the goldfish for intensity discrimination were studied using classical respiratory conditioning and a staircase psychophysical procedure. Physiological studies on single saccular (auditory) nerve fibers under similar stimulus conditions helped characterize the dimensions of neural activity used in intensity discrimination. Incremental intensity difference limens (IDLs in dB) for 160-ms increments in continuous noise, 500-ms noise bursts, and 500-ms, 800-Hz tone bursts are 2 to 3 dB, are independent of overall level, and vary with signal duration according to a power function with a slope averaging - 0.33. Noise decrements are relatively poorly detected and the silent gap detection threshold is about 35 ms. The IDLs for increments and decrements in an 800-Hz continuous tone are about 0.13 dB, are independent of duration, and are level dependent. Unlike mammalian auditory nerve fibers, some goldfish saccular fibers show variation in recovery time to tonal increments and decrements, and adaptation to a zero rate. Unit responses to tone increments and decrements show rate effects generally in accord with previous observations on intracellular epsp's in goldfish saccular fibers. Neurophysiological correlates of psychophysical intensity discrimination data suggest the following: (1) noise gap detection may be based on spike rate increments which follow gap offset; (2) detection of increments and decrements in continuous tones may be determined by steep low-pass filtering in peripheral neural channels which enhance the effects of spectral "splatter" toward the lower frequencies; (3) IDLs for pulsed signals of different duration can be predicted from the slopes of rate-intensity functions and spike rate variability in individual auditory nerve fibers; and (4) at different sound pressure levels, different populations of peripheral fibers provide the information used in intensity discrimination.     

Intensity discrimination, increment detection, and magnitude estimation for 1-kHz tones

Intensity difference limens (DLs) were measured over a wide intensity range for 200-ms, 1-kHz gated tones and for 200-ms increments in continuous 1-kHz tones. Magnitude estimates also were obtained for the gated tones over a comparable intensity range. The discrimination data are in general agreement with those from earlier studies but they extend them by showing: (1) good discrimination for gated tones over at least a 115-dB dynamic range; (2) a slight increase in the relative DL (delta I/I) as intensity increases above 95 dB SPL; (3) smaller DLs for increments than for gated tones, with the difference approximately independent of intensity; (4) negligible "negative masking" when thresholds are expressed as intensity differences (delta I). For two of the three subjects, magnitude estimates do not conform to a single-exponent power law for suprathreshold intensities. Over the middle range of intensities where a single exponent is appropriate, the value of the exponent is less than 0.1 for all subjects.     

Effects of stimulus and noise rate variability on speech perception by younger and older adults

The present experiments examine the effects of listener age and hearing sensitivity on the ability to understand temporally altered speech in quiet when the proportion of a sentence processed by time compression is varied. Additional conditions in noise investigate whether or not listeners are affected by alterations in the presentation rate of background speech babble, relative to the presentation rate of the target speech signal. Younger and older adults with normal hearing and with mild-to-moderate sensorineural hearing losses served as listeners. Speech stimuli included sentences, syntactic sets, and random-order words. Presentation rate was altered via time compression applied to the entire stimulus or to selected phrases within the stimulus. Older listeners performed more poorly than younger listeners in most conditions involving time compression, and their performance decreased progressively with the proportion of the stimulus that was processed with time compression. Older listeners also performed more poorly than younger listeners in all noise conditions, but both age groups demonstrated better performance in conditions incorporating a mismatch in the presentation rate between target signal and background babble compared to conditions with matched rates. The age effects in quiet are consistent with the generalized slowing hypothesis of aging. Performance patterns in noise tentatively support the notion that altered rates of speech signal and background babble may provide a cue to enhance auditory figure-ground perception by both younger and older listeners.     

Vowel perception by noise masked normal-hearing young adults

This study examined vowel perception by young normal-hearing (YNH) adults, in various listening conditions designed to simulate mild-to-moderate sloping sensorineural hearing loss. YNH listeners were individually age- and gender-matched to young hearing-impaired (YHI) listeners tested in a previous study [Richie et al., J. Acoust. Soc. Am. 114, 2923-2933 (2003)]. YNH listeners were tested in three conditions designed to create equal audibility with the YHI listeners; a low signal level with and without a simulated hearing loss, and a high signal level with a simulated hearing loss. Listeners discriminated changes in synthetic vowel tokens /I e epsilon alpha ae/ when Fl or F2 varied in frequency. Comparison of YNH with YHI results failed to reveal significant differences between groups in terms of performance on vowel discrimination, in conditions of similar audibility by using both noise masking to elevate the hearing thresholds of the YNH and applying frequency-specific gain to the YHI listeners. Further, analysis of learning curves suggests that while the YHI listeners completed an average of 46% more test blocks than YNH listeners, the YHI achieved a level of discrimination similar to that of the YNH within the same number of blocks. Apparently, when age and gender are closely matched between young hearing-impaired and normal-hearing adults, performance on vowel tasks may be explained by audibility alone.     

Psychometric functions for discrimination of two-component complex tones in listeners with normal hearing and listeners with hearing loss

This study compared the ability of 5 listeners with normal hearing and 12 listeners with moderate to moderately severe sensorineural hearing loss to discriminate complementary two-component complex tones (TCCTs). The TCCTs consist of two pure tone components (f1 and f2) which differ in frequency by delta f (Hz) and in level by delta L (dB). In one of the complementary tones, the level of the component f1 is greater than the level of component f2 by the increment delta L; in the other tone, the level of component f2 exceeds that of component f1 by delta L. Five stimulus conditions were included in this study: fc = 1000 Hz, delta L = 3 dB; fc = 1000 Hz, delta L = 1 dB; fc = 2000 Hz, delta L = 3 dB; fc = 2000 Hz, delta L = 1 dB; and fc = 4000 Hz, delta L = 3 dB. In listeners with normal hearing, discrimination of complementary TCCTs (with a fixed delta L and a variable delta f) is described by an inverted U-shaped psychometric function in which discrimination improves as delta f increases, is (nearly) perfect for a range of delta f's, and then decreases again as delta f increases. In contrast, group psychometric functions for listeners with hearing loss are shifted to the right such that above chance performance occurs at larger values of delta f than in listeners with normal hearing. Group psychometric functions for listeners with hearing loss do not show a decrease in performance at the largest values of delta f included in this study. Decreased TCCT discrimination is evident when listeners with hearing loss are compared to listeners with normal hearing at both equal SPLs and at equal sensation levels. In both groups of listeners, TCCT discrimination is significantly worse at high center frequencies. Results from normal-hearing listeners are generally consistent with a temporal model of TCCT discrimination. Listeners with hearing loss may have deficits in using phase locking in the TCCT discrimination task and so may rely more on place cues in TCCT discrimination.     

Monaural and binaural loudness of 5- and 200-ms tones in normal and impaired hearing

The difference in level required to match monaural and binaural loudness of 5- and 200-ms tones was measured for listeners with normal and impaired hearing. Stimuli were 1-kHz tones presented at levels ranging from 10 to 90 dB sensation level. Sixteen listeners (eight normal and eight with losses of primarily cochlear origin) made loudness matches between equal-duration monaural and binaural tones using an adaptive 2AFC procedure. The present results corroborate existing data for 200-ms tones in normal listeners and provide new data for 5-ms tones. On average, the binaural level difference required for equal loudness of monaural and binaural tones is about the same for 5- and 200-ms tones of equal level and changes as a function of level. The group data for normal and impaired listeners are in reasonable agreement with data in the literature. However, the data from some of the impaired listeners deviate markedly from the average, indicating that group data do not accurately represent the behavior of all impaired listeners. Derived loudness functions from the loudness-matching data are reasonably consistent with individual data in the literature.     

Virtual pitch integration for asynchronous harmonics

This experiment examined the generation of virtual pitch for harmonically related tones that do not overlap in time. The interval between successive tones was systematically varied in order to gauge the integration period for virtual pitch. A pitch discrimination task was employed, and both harmonic and nonharmonic tone series were tested. The results confirmed that a virtual pitch can be generated by a series of brief, harmonically related tones that are separated in time. Robust virtual pitch information can be derived for intervals between successive 40-ms tones of up to about 45 ms, consistent with a minimum estimate of integration period of about 210 ms. Beyond intertone intervals of 45 ms, performance becomes more variable and approaches an upper limit where discrimination of tone sequences can be undertaken on the basis of the individual frequency components. The individual differences observed in this experiment suggest that the ability to derive a salient virtual pitch varies across listeners.     

Auditory spatial discrimination by barn owls in simulated echoic conditions

In humans, directional hearing in reverberant conditions is characterized by a "precedence effect," whereby directional information conveyed by leading sounds dominates perceived location, and listeners are relatively insensitive to directional information conveyed by lagging sounds. Behavioral studies provide evidence of precedence phenomena in a wide range of species. The present study employs a discrimination paradigm, based on habituation and recovery of the pupillary dilation response, to provide quantitative measures of precedence phenomena in the barn owl. As in humans, the owl's ability to discriminate changes in the location of lagging sources is impaired relative to that for single sources. Spatial discrimination of lead sources is also impaired, but to a lesser extent than discrimination of lagging sources. Results of a control experiment indicate that sensitivity to monaural cues cannot account for discrimination of lag source location. Thus, impairment of discrimination ability in the two-source conditions most likely reflects a reduction in sensitivity to binaural directional information. These results demonstrate a similarity of precedence effect phenomena in barn owls and humans, and provide a basis for quantitative comparison with neuronal data from the same species.     

Temporal masking functions for listeners with real and simulated hearing loss

A functional simulation of hearing loss was evaluated in its ability to reproduce the temporal masking functions for eight listeners with mild to severe sensorineural hearing loss. Each audiometric loss was simulated in a group of age-matched normal-hearing listeners through a combination of spectrally-shaped masking noise and multi-band expansion. Temporal-masking functions were obtained in both groups of listeners using a forward-masking paradigm in which the level of a 110-ms masker required to just mask a 10-ms fixed-level probe (5-10 dB SL) was measured as a function of the time delay between the masker offset and probe onset. At each of four probe frequencies (500, 1000, 2000, and 4000 Hz), temporal-masking functions were obtained using maskers that were 0.55, 1.0, and 1.15 times the probe frequency. The slopes and y-intercepts of the masking functions were not significantly different for listeners with real and simulated hearing loss. The y-intercepts were positively correlated with level of hearing loss while the slopes were negatively correlated. The ratio of the slopes obtained with the low-frequency maskers relative to the on-frequency maskers was similar for both groups of listeners and indicated a smaller compressive effect than that observed in normal-hearing listeners.     

Temporal order discrimination of tonal sequences by younger and older adults: the role of duration and rate

The effect of tone duration and presentation rate on the discrimination of the temporal order of the middle two tones of a four-tone sequence was investigated in young normal-hearing (YNH) and older hearing-impaired (OHI) listeners. The frequencies and presentation level of the tone sequences were selected to minimize the effect of hearing loss on the performance of the OHI listeners. Tone durations varied from 20 to 400 ms and presentation rates from 2.5 to 25 toness. Two experiments were conducted with anisochronous (nonuniform duration and rate across entire sequence) and isochronous (uniform rate and duration) sequences, respectively. For the YNH listeners, performance for both isochronous and anisochronous sequences was determined primarily by presentation rate such that performance decreased at rates faster than 5 toness. For anisochronous tone sequences alone, the effects of rate were more pronounced at short tone durations. For the OHI listeners, both presentation rate and tone duration had an impact on performance for both isochronous and anisochronous sequences such that performance decreased as rate increased above 5 toness or duration decreased below 40 ms. Temporal masking was offered as an explanation for the interaction of short durations and fast rates on temporal order discrimination for the anisochronous sequences.