Decline of speech understanding and auditory thresholds in the elderly.

A group of 29 elderly subjects between 60.0 and 83.7 years of age at the beginning of the study, and whose hearing loss was not greater than moderate, was tested twice, an average of 5.27 years apart. The tests measured pure-tone thresholds, word recognition in quiet, and understanding of speech with various types of distortion (low-pass filtering, time compression) or interference (single speaker, babble noise, reverberation). Performance declined consistently and significantly between the two testing phases. In addition, the variability of speech understanding measures increased significantly between testing phases, though the variability of audiometric measurements did not. A right-ear superiority was observed but this lateral asymmetry did not increase between testing phases. Comparison of the elderly subjects with a group of young subjects with normal hearing shows that the decline of speech understanding measures accelerated significantly relative to the decline in audiometric measures in the seventh to ninth decades of life. On the assumption that speech understanding depends linearly on age and audiometric variables, there is evidence that this linear relationship changes with age, suggesting that not only the accuracy but also the nature of speech understanding evolves with age.

The Times of Ira Hirsh: Multiple Ranges of Auditory Temporal Perception.

Ira Hirsh was among the first to recognize that the auditory system does not deal with temporal information in a unitary way across the continuum of time intervals involved in speech processing. He identified the short range (extending from 1 to 20 milliseconds) as that of phase perception, the range between 20 and 100 milliseconds as that in which auditory patterns emerge, and the long range from 100 milliseconds and longer as that of separate auditory events. Furthermore, he also was among the first to recognize that auditory time perception heavily depended on spectral context. A study of the perception of sequences representing different temporal orders of three tones, by Hirsh and the author (e.g., Divenyi and Hirsh, 1978) demonstrated the dependence of auditory sequence perception on both time range and spectral context, and provided a bridge between Hirsh's view of auditory time and Bregman's view of stream segregation. A subsequent search by the author for psychophysical underpinnings of the cocktail-party phenomenon (e.g., Divenyi and Haupt, 1997) suggests that segregation of simultaneous streams of speech might rely on the ability to follow spectral changes in the demisyllabic-to-syllabic (100 to 200 milliseconds) range (i.e., Hirsh's long range).Learning Outcomes: As a result of this activity, the participant will be able to (1) describe the importance of temporal processing in hearing; and (2) identify time ranges where the auditory system will spontaneously adopt different analysis techniques.

Lateralization of narrow-band noise by blind and sighted listeners.

The effects of varying interaural time delay (ITD) and interaural intensity difference (IID) were measured in normal-hearing sighted and congenitally blind subjects as a function of eleven frequencies and at sound pressure levels of 70 and 90 dB, and at a sensation level of 25 dB (sensation level refers to the pressure level of the sound above its threshold for the individual subject). Using an 'acoustic' pointing paradigm, the subject varied the IID of a 500 Hz narrow-band (100 Hz) noise (the 'pointer') to coincide with the apparent lateral position of a 'target' ITD stimulus. ITDs of 0, +/-200, and +/-400 micros were obtained through total waveform delays of narrow-band noise, including envelope and fine structure. For both groups, the results of this experiment confirm the traditional view of binaural hearing for like stimuli: non-zero ITDs produce little perceived lateral displacement away from 0 IID at frequencies above 1250 Hz. To the extent that greater magnitude of lateralization for a given ITD, presentation level, and center frequency can be equated with superior localization abilities, blind listeners appear at least comparable and even somewhat better than sighted subjects, especially when attending to signals in the periphery. The present findings suggest that blind listeners are fully able to utilize the cues for spatial hearing, and that vision is not a mandatory prerequisite for the calibration of human spatial hearing.