Individual differences in objective effects of noise on performance were analyzed with respect to their distribution, temporal stability, and the precision of measurement to be attained. Seventy-two subjects had to memorize sequences of visually presented digits while being exposed to one of three auditory background conditions which were randomly mixed on a trial-by-trial basis: (1) foreign speech; (2) pink noise; and (3) silence. Individual "irrelevant speech effects," operationalized by the difference in recall errors under speech and in silence, were normally distributed over a wide range extending from slight facilitation to severe disruption. When 25 subjects repeated the experiment after four weeks, the individual differences were replicated with a reliability of rtt = 0.45. Internal consistency, a measure of the precision with which individual effects can be measured in a single session, was moderate (alpha = 0.55). However, both retest, and consistency coefficients are severely attenuated by the use of (sound-minus-silence) difference scores, the reliability of which is bound to be considerably lower than that of the original error scores whenever these are correlated. Given that the original error rates in a specific auditory condition can be determined with reliabilities approaching 0.85, it may be concluded that individual performance decrements due to noise can be reliably measured in the "irrelevant speech" paradigm. Self-report measures of noise susceptibility collected to explore potential sources of the large inter-individual variation exhibited only weak relationships with the objectively measured noise effects: Subjects were quite inaccurate in assessing their individual impairment in the three auditory conditions, and a questionnaire-based measure of general noise sensitivity only accounted for a small portion of the variance in objectively measured performance decrements, although in both cases the predictive relationship was much stronger in female than in male subjects.

No abstract

In environmental noise surveys, self-reported noise sensitivity, a stable personality trait covering attitudes toward a wide range of environmental sounds, is a major predictor of individual noise-annoyance reactions. Its relationship to basic measures of auditory functioning, however, has not been systematically explored. Therefore, in the present investigation, a sample of 61 unselected listeners was subjected to a battery of psychoacoustic procedures ranging from threshold determinations to loudness scaling tasks. No significant differences in absolute thresholds, intensity discrimination, simple auditory reaction time, or power-function exponents for loudness emerged, when the sample was split along the median into two groups of "low" vs "high" noise sensitivity on the basis of scores obtained from a psychometrically evaluated questionnaire [Zimmer and Ellermeier, Diagnostica 44, 11-20 (1998)]. Small, but systematic differences were found in verbal loudness estimates, and in ratings of the unpleasantness of natural sounds, thus suggesting that self-reported noise sensitivity captures evaluative rather than sensory aspects of auditory processing.

The decrement in memory performance observed while listeners are being exposed to acoustically structured stimuli is called the irrelevant sound effect (ISE). The present review summarizes the research identifying physical features of the irrelevant background that reliably induce performance decrements. It shows that speech, or speech analogues, produce the largest effects by far, suggesting that speech-specific features may contribute to auditory distraction. When an attempt is made to isolate psychoacoustical parameters contributing to the effect, it turns out that noticeable spectral change over time is a necessary condition to observe an ISE, while level change by itself is not. New empirical evidence is presented determining the rate of frequency modulation at which maximal effects are obtained. Results of a further study employing noise-vocoded speech show the importance of spectral detail in producing an ISE. At present, the wealth of empirical findings on the effects of irrelevant sound is not well accounted for by the available theoretical models. Cognitive models make only qualitative predictions, and psychoacoustical models (e.g., those based on fluctuation strength or the speech transmission index) account for subsets of the available data, but have thus far failed to capture the combined effects of temporal structure and spectral change in generating the interference.

No abstract