Bruce A. Schneider

Gap detection and the precedence effect in young and old adults

Thresholds for detecting a gap between two Gaussian-enveloped (standard deviation = 0.5 ms), 2-kHz tones were determined in young and old listeners. The gap-detection thresholds of old adults were more variable and about twice as large as those obtained from young adults. Moreover, gap-detection thresholds were not correlated with audiometric thresholds in either group. Estimates of the width of the temporal window of young subjects, based on the detection of a gap between two tone pips, were smaller than those typically obtained when a relatively long duration pure tone is interrupted [Moore et al., J. Acoust. Soc. Am. 85, 1266-1275 (1989)]. Because the amount of time it takes to recover from an adapting stimulus is likely to affect gap detection thresholds [Glasberg et al., J. Acoust. Soc. Am. 81, 1546-1556 (1987)], smaller estimates of temporal window size would be expected in this paradigm if the amount of adaptation produced by the first tone pip was negligible. The larger gap-detection thresholds of old subjects indicate that they may have larger temporal windows than young subjects. The lack of correlation between audiometric and gap-detection thresholds indicates that this loss of temporal acuity is not related to the degree of sensorineural hearing loss. In a second experiment on the precedence effect using the same subjects, a Gaussian-enveloped tone was presented over earphones to the left ear followed by the same tone pip presented to the right ear. To more realistically approximate a sound field situation, the tone pip presented to each ear was followed 0.6 ms later by an attenuated version presented to the contralateral ear. The delay between the left- and right-ear tone-pips was varied and the transition point between hearing a single tone on the left, and hearing two such sounds in close succession (one coming from the left and the other from the right) was determined. The transition point in this experiment did not differ between young and old subjects nor were these transition points correlated with gap-detection thresholds. These results indicate that monaural temporal acuity and binaural echo suppression may be based on different processes.

Comparing the effects of aging and background noise on short-term memory performance

Paired associate recall was tested as a function of serial position for younger and older adults for five word pairs presented aurally in quiet and in noise. In Experiment 1, the addition of noise adversely affected recall in young adults, but only in the early serial positions. Experiments 2 and 3 suggested that the recall of older adults listening to the words in quiet was nearly equivalent to that of younger adults listening in noise. In Experiment 4, we determined the signal-to-noise ratio (S/N) such that, on average, younger and older adults were able to correctly hear the same percentage of words when words were presented one at a time in noise. In Experiment 5, younger adults were tested under this S/N. Compared with older adults from Experiment 3, younger adults in this experiment recalled more words at all serial positions. The results are interpreted as showing that encoding in secondary memory is impaired by aging and noise either as a function of degraded sensory representations, or as a function of reduced processing resources.

Gap detection thresholds as a function of tonal duration for younger and older listeners

Twenty normal hearing younger and twenty older adults in the early stages of presbycusis, but with relatively normal hearing at 2 kHz, were asked to discriminate between the presence versus absence of a gap between two equal-duration tonal markers. The duration of each marker was constant within a block of trials but varied between 0.83 and 500 ms across blocks. Notched-noise, centered at 2 kHz, was used to mask on- and off-transients. Gap detection thresholds of older adults were markedly higher than those of younger adults for marker durations of less than 250 ms but converged on those of younger adults at 500 ms. For both age groups, gap detection thresholds were independent of audiometric thresholds. These results indicate that older adults have more difficulty detecting a gap than younger adults when short marker durations (i.e., durations characteristic of speech sounds) are employed. It is shown that these results cannot be explained by linear models of temporal processing but are consistent with differential adaptation effects in younger and older adults.

Human temporal auditory acuity as assessed by envelope following responses.

Temporal auditory acuity, the ability to discriminate rapid changes in the envelope of a sound, is essential for speech comprehension. Human envelope following responses (EFRs) recorded from scalp electrodes were evaluated as an objective measurement of temporal processing in the auditory nervous system. The temporal auditory acuity of older and younger participants was measured behaviorally using both gap and modulation detection tasks. These findings were then related to EFRs evoked by white noise that was amplitude modulated (25% modulation depth) with a sweep of modulation frequencies from 20 to 600 Hz. The frequency at which the EFR was no longer detectable was significantly correlated with behavioral measurements of gap detection (r = -0.43), and with the maximum perceptible modulation frequency (r = 0.72). The EFR techniques investigated here might be developed into a clinically useful objective estimate of temporal auditory acuity for subjects who cannot provide reliable behavioral responses.

Temporal jitter disrupts speech intelligibility : A simulation of auditory aging

We disrupted periodicity cues by temporally jittering the speech signal to explore how such distortion might affect word identification. Jittering distorts the fine structure of the speech signal with negligible alteration of either its long-term spectral or amplitude envelope characteristics. In Experiment 1, word identification in noise was significantly reduced in young, normal-hearing adults when sentences were temporally jittered at frequencies below 1.2kHz. The accuracy of the younger adults in identifying jittered speech in noise was similar to that found previously for older adults with good audiograms when they listened to intact speech in noise. In Experiment 2, to rule out the possibility that the reductions in word identification were due to spectral distortion, we also tested a simulation of cochlear hearing loss that produced spectral distortion equivalent to that produced by jittering, but this simulation had significantly less temporal distortion than was produced by jittering. There was no significant reduction in the accuracy of word identification when only the frequency region below 1.2kHz was spectrally distorted. Hence, it is the temporal distortion rather than the spectral distortion of the low-frequency components that disrupts word identification.

Individual loudness functions determined from direct comparisons of loudness intervals

Five subjects were required in each trial to directly compare two pairs of tones and indicate which pair of tones had the greater loudness difference. Ten 1,200-Hz tones differing only in intensity were employed. Subjects made binary comparisons among the 45 tone pairs that can be formed from these 10 tones. The loudness difference comparisons of each subject were found to satisfy two properties (transitivity and monotonicity) that are required for an interval scale representation of loudness. Therefore, individual loudness scales were constructed using a nonmetric scaling technique designed for comparisons of sensory intervals. These loudness scales differed significantly from subject to subject. Since a nonnumerical scaling procedure was employed, these individual differences could not be attributed to biases in the way in which observers use numbers or numerical concepts to describe the loudness of tones. Hence, they suggest strong individual differences in the coding of sound intensity.

Effects of Senescent Changes in Audition and Cognition on Spoken Language Comprehension

Older individuals often find it difficult to communicate, especially in group situations, because they are unable to keep up with the flow of conversation or are too slow in comprehending what they are hearing. These communication difficulties are often exacerbated by negative stereotypes held by their communication partners who often perceive older adults as less competent than they actually are (Ryan et al. 1986). Sometimes, older adults’ communication problems motivate them, often at the prompting of their family and friends, to seek help from hearing specialists (O’Mahoney et al. 1996). Quite often, however, older adults and/or their family members wonder if these comprehension difficulties are a sign of cognitive decline. Such uncertainty on the part of both older adults and their family members with respect to the source of communication difficulties is understandable given that age-related changes in the comprehension of spoken language could be due to age-related changes in hearing, to age-related declines in cognitive functioning, or to interactions between these two levels of processing. To participate effectively in a multitalker conversation, listeners need to do more than simply recognize and repeat speech. They have to keep track of who said what, extract the meaning of each utterance, store it in memory for future use, integrate the incoming information with what each conversational participant has said in the past, and draw on the listener’s own knowledge of the topic under consideration to extract general themes and formulate responses. In other words, effective communication requires not only an intact auditory system but also an intact cognitive system.

Developmental Changes in Infants' Sensitivity to Octave-Band Noises

Abstract Localization responses to octave-band noises with center frequencies at 200, 400, 1000, 2000, 4000, and 10,000 Hz were obtained from infants 6, 12, and 18 months of age. During an experimental trial, an octave-band noise was presented on one of two speakers located 45° to each side of the infant. A head turn to the noise (correct response) was rewarded by activating an animated toy on top of the speaker. The intensity of the noise was varied over trials (method of constant stimuli) to determine thresholds at each center frequency. Thresholds for the lower frequencies were approximately 5–8 db higher in the 6-month-old infants compared to the older infants. However, there were no consistent differences among groups at the higher frequencies. Infant thresholds were found to be 20–30 db higher than adult thresholds at the lower frequencies. At the higher frequencies thresholds for infants were approaching those of adults.

Does stimulus context affect loudness or only loudness judgments

Marks (1988) reported that when equal-loudness matches were inferred from magnitude estimates of loudness for tones of two different frequencies, the matches were affected by changes in the stimulus intensity range at both frequencies. Marks interpreted these results as reflecting the operation of response biases in the subjects’ estimates; that is, the effect of range was to alter subjects’ judgments but not necessarily the perception of loudness itself. We investigated this effect by having subjects choose which of two tone pairs defined the larger loudness interval. By using tones of two frequencies, and varying their respective intensity ranges, we reproduced Marks’ result in a procedure devoid of numerical responses. When the tones at one frequency are all soft, but the tones at the other frequency are not all soft, cross-frequency loudness matches are different from those obtained with other intensity range combinations. This suggests that stimulus range affects the perception of loudness in addition to whatever effects it may have on numerical judgments of loudness.

The perceptual basis of loudness ratio judgments

In Experiment 1, subjects were required to estimateloudness ratios for 45 pairs of tones. Ten 1,200-Hz tones, differing only in intensity, were used to generate the 45 distinct tone pairs. In Experiment 2, subjects were required to directly compare two pairs of tones (chosen from among the set of 45) and indicate which pair of tones had the greaterloudness ratio. In both Experiments 1 and 2, the subjects’ judgments were used to rank order the tone pairs with respect to their judged loudness ratios. Nonmetric analyses of these rank orders indicated that both magnitude estimates of loudness ratios and direct comparisons of loudness ratios were based on loudnessintervals ordifferences where loudness was a power function of sound pressure. These experiments, along with those on loudness difference judgments (Parker & Schneider, 1974; Schneider, Parker, & Stein, 1974), support Torgerson’s (1961) conjecture that there is but one comparative perceptual relationship for ioudnesses, and that differences in numerical estimates for loudness ratios as opposed to loudness intervals simply reflect different reporting strategies generated by the two sets of instructions.