Duration Difference Limens Research Articles

Age effects in discrimination of intervals within accented tone sequences differing in accent type and sequence presentation rate.

The study measured listener sensitivity to increments in the duration of one or two target silent intervals embedded within unaccented tone sequences and sequences that featured a single accented component. The baseline unaccented sequences consisted of six 1000-Hz 40-ms tone bursts that were separated equally by silent intervals to establish a slower tone sequence rate, with tonal inter-onset intervals (IOIs) set to 200 ms, or a faster rate with tonal IOIs set to 100 ms. Stimulus accent was created by doubling the baseline duration of a single sequence component, either the second tone burst (tonal accent), or the second tonal IOI (interval accent). Duration difference limens for increments of the target interval(s) were measured adaptively by varying a single inter-tone silent interval or co-varying two successive inter-tone silent intervals; target intervals occurred at the third, or third and fourth, sequence locations. Listeners included younger normal-hearing adults and groups of older listeners with and without hearing loss. Discrimination for the two older groups was equivalent and poorer than that of the younger listeners, especially for the faster accented sequences. Discrimination was best for stimuli with two successive target intervals, indicating that target repetition within accented sequences acts to improve listener temporal sensitivity.

Developmental changes in the perception of syllable-final stop voicing are not explained by age-related differences in auditory sensitivity

Two cues to voicing decisions for syllable-final stops are vocalic duration and formant transitions, especially F1, at syllable offset. Developmental studies show that children weight vocalic duration less and formant transitions more than adults. This study tested the hypothesis that age-related differences in auditory sensitivity can explain these developmental changes by measuring adults’ and children’s sensitivities to changes in the duration of nonspeech, complex tones and analogous speech stimuli. The durations of three-tone sinusoidal stimuli and natural cob and cop were varied. Duration difference limens (DLs) were similar for listeners across ages, and similar for nonspeech and speech. Also, the extent of frequency fall was varied in three-tone sinusoidal stimuli for the first tone (T1) only or for all three tones, as well as for F1 only in synthetic buck/bug. DLs for frequency extent were similar for listeners across ages for nonspeech stimuli when all three tones fell, but children had larger DLs than adults when only T1 or F1 fell, a finding contrary to labeling results showing that children weight this very property more than adults. Overall the evidence contradicted the hypothesis that age-related differences in auditory sensitivity can explain developmental changes in the perception of syllable-final stop voicing.

Effect of age on silent gap discrimination in synthetic speech stimuli.

The difficulty that older listeners experience understanding conversational speech may be related to their limited ability to use information present in the silent intervals (i.e., temporal gaps) between dynamic speech sounds. When temporal gaps are present between nonspeech stimuli that are spectrally invariant (e.g., noise bands or sinusoids), older listeners are less able to resolve temporal gaps than are younger listeners. It has also been demonstrated that temporal gap perception deteriorates as the frequency difference between the sounds bordering the silent gap increases, and this effect becomes more pronounced with age (J. Lister, J. Besing, and J. Koehnke, 2002; J. Lister, J. Koehnke, and J. Besing, 2000). In this study, the effect of age on the ability to discriminate temporal gaps in dynamic stimuli (i.e., changing in frequency and duration over time) was measured in a gap duration discrimination (GDD) task. The participants were two groups of listeners with normal hearing sensitivity through at least 4000 Hz: (a) ages 21-38 years and (b) ages 50-72 years. Stimuli simulated the frequency characteristics of 1 consonant (/s/), a steady-state vowel (/a/), a weak diphthong (/eI/), and a voiced bilabial plosive (/burst/) in 6 combinations: (a) /s-a/, (b) /s-eI/, (c) /a-a/, (d) /eI-eI/, (e) /burst-a/, and (f) /burst-eI/. For each of the 6 phoneme combinations, 2 conditions of stimulus duration were used: (a) fixed, meaning that the durations of leading and trailing noises were fixed at values typical for the speech sounds being simulated, and (b) random, meaning that duration varied randomly within a range acceptable for accurate perception of the speech contrasts. Gap duration difference limens (GDDLs) were significantly larger for the older listeners than for younger listeners. For both groups, GDDLs were poorer for the spectrally dynamic marker pairs (e.g., /burst-eI/) than for the marker pairs that were relatively stable in frequency over time (/a-a/). GDD performance also was poorer for the random conditionthan for the fixed condition. Listener age and hearing sensitivity were significantly correlated, and age was not significantly correlated with GDD when controlling for hearing sensitivity. The authors conclude that temporal resolution (as measured by gap discrimination) is affected by age, stimulus complexity, and, perhaps, by hearing sensitivity in a speech context.

Effects of age and frequency disparity on gap discrimination.

Temporal discrimination was measured using a gap discrimination paradigm for three groups of listeners with normal hearing: (1) ages 18-30, (2) ages 40-52, and (3) ages 62-74 years. Normal hearing was defined as pure-tone thresholds < or = 25 dB HL from 250 to 6000 Hz and < or = 30 dB HL at 8000 Hz. Silent gaps were placed between 1/4-octave bands of noise centered at one of six frequencies. The noise band markers were paired so that the center frequency of the leading marker was fixed at 2000 Hz, and the center frequency of the trailing marker varied randomly across experimental runs. Gap duration discrimination was significantly poorer for older listeners than for young and middle-aged listeners, and the performance of the young and middle-aged listeners did not differ significantly. Age group differences were more apparent for the more frequency-disparate stimuli (2000-Hz leading marker followed by a 500-Hz trailing marker) than for the fixed-frequency stimuli (2000-Hz lead and 2000-Hz trail). The gap duration difference limens of the older listeners increased more rapidly with frequency disparity than those of the other listeners. Because age effects were more apparent for the more frequency-disparate conditions, and gap discrimination was not affected by differences in hearing sensitivity among listeners, it is suggested that gap discrimination depends upon temporal mechanisms that deteriorate with age and stimulus complexity but are unaffected by hearing loss.

Audiological Assessment of Profoundly Hearing-Impaired Children

The design of an audiological assessment protocol for profoundly hearing-impaired children may be divided into three areas. First, accurate estimation of hearing loss includes the behavioral measures of unaided and aided thresholds and the objective measures of electrocochleography and auditory brain stem response. The reliability of these measures for the accurate diagnosis of a profound to total hearing loss is discussed. Second, speech perception includes the measure of perception in the audition alone, vision alone, and audition plus vision conditions. Test material should include speech features, words, and sentences. Factors influencing the choice of material are the developmental age of the child, the method of educational instruction, speech and language skills, and vocabulary limits. Third, psychophysical properties of residual auditory skills include measures such as frequency, intensity, and duration difference limens. These skills may be compared to those elicited through other sensory channels, such as visual and tactile. Other important factors that should be considered are the psychological well-being of the child and family, family motivations and expectations, and educational requirements.

Psychophysical studies on prelingual patients using a multiple electrode cochlear implant

Psychophysical studies were conducted on three prelingual patients during the first year of usage of a multiple electrode cochlear implant. The results were compared with those obtained from postlingual patients. For the identification of two electrode positions (6 mm apart), the d′ sensitivity index for prelinguals was <0.75 and for postlinguals > 3.0. For the identification of two electric repetition rates (an octave apart), d′ for prelinguals was <0.6 and >3.0 for postlinguals. Temporal resolution discrimination was also poorer for prelinguals, gap detection >64 ms and duration difference limens >38 ms from a fixed standard duration of 30 ms, while for postlinguals, <3 ms and <38 ms, respectively. The ability to count a variable number of short electrical stimuli deteriorated at high rates (>5/s) of presentation for prelinguals but not for postlinguals, while for visual and tactile stimuli performance was similar across all patients. However, improvements in one prelingual patient after one year of usage were recorded for electrode place and rate identification (d′ > 1.5).

Behavior and psychophysics of hearing in birds

Psychophysical investigations of hearing in a number of avian species over the last decade have added significantly to our knowledge of hearing capabilities characteristic of this vertebrate group. Behavioral measures of absolute auditory sensitivity in a wide variety of bird species show a region of maximum sensitivity between 1 and 5 kHz with a rapid decrease in sensitivity at higher frequencies. On the basis of this general measure, birds fall between two other major vertebrate groups: reptiles and mammals. Discrimination and masking data from birds include measures of frequency, intensity, and duration difference limens; critical ratios, critical bands, and psychophysical tuning curves. There are also data on temporal summation, temporal resolving power, and temporary threshold shift from noise exposure. Taken together these data suggest that, in the region of 1–5 kHz, birds show a level of hearing sensitivity similar in most respects to that found for the most sensitive members of the class Mammalia with avian performance clearly inferior above and below this range of frequencies. Possible exceptions to this general picture must include the echolocating oilbird and growing evidence that pigeons are sensitive to infrasound at moderate intensity levels. The relation among critical ratio, critical band, and intensity difference limen measures in the parakeet is similar to that described for the human, but the pattern of masking as a function of frequency is dramatically different from that observed in mammals. Examples of a correspondence between hearing sensitivity and vocalizations can be demonstrated in a number of species.

Perception of auditory temporality in several species of birds

Thresholds for the detection of gaps in noise, temporal integration, and difference limens for duration were measured in several species of birds using avoidance conditioning and the method of limits procedures previously described for the parakeet. The threshold for the detection of gaps in white noise bursts is about 3–5 msec for the house finch. Temporal integration functions showing absolute threshold as a function of tone duration for field sparrows and parakeets reveal a “time constant” of 200–300 msec. Difference limens for duration obtained at six durations of a 2.86-kHz tone for the parakeet show Weber fractions, ΔD/D, in the range of 0.10–0.20. These data are compared to similar data available for the human and the results of these experiments are discussed in relation to the characteristics of avain vocalizations and the role of hearing in song learning and song production. [Work supported by NSF grant BNS75-19431.]

The Syllable Nucleus as a Unit of Timing

The paper explores the question whether resonants preceding and following a vowel can be considered as part of the syllable nucleus. A set of monosyllabic words was studied, beginning and ending with voiced and voiceless obstruent consonants, and containing syllable nuclei of the following types: V (long and short), V+R, R+V, and R+V+R. Three speakers produced each of the 156 words five times. An analysis of the durations of the segments yields (a) that syllable nuclei consisting of V+R function as a unit with respect to the timing patterns conditioned by the voicing of the following consonant, and (b) that resonants combine with long vowels in such a way that the durational differences between syllable nuclei of the types V, V+R, and R+V are below the perceptual level (i.e., below established difference limens for duration). The evidence is considered as supportive of the assumption that timing in speech is organized with reference to major changes in manner of articulation.