Psychoacoustic correlates of individual noise sensitivity.

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.

Empirical evaluation of axioms fundamental to Stevens's ratio-scaling approach: I. Loudness production.

Stevens's direct scaling methods rest on the assumption that subjects are capable of reporting or producing ratios of sensation magnitudes. Only recently, however, did an axiomatization proposed by Narens (1996) specify necessary conditions for this assumption that may be put to an empirical test. In the present investigation, Narens's central axioms of commutativity and multiplicativity were evaluated by having subjects produce loudness ratios. It turned out that the adjustments were consistent with the commutativity condition; multiplicativity (the fact that consecutive doubling and tripling of loudness should be equivalent to making the starting intensity six times as loud), however, was violated in a significant number of cases. According to Narens's (1996) axiomatization, this outcome implies that although in principle a ratio scale of loudness exists, the numbers used by subjects to describe sensation ratios may not be taken at face value.

Is level irrelevant in "irrelevant speech"? Effects of loudness, signal-to-noise ratio, and binaural unmasking.

A series of experiments explored the role of level, signal-to-noise ratio, and the masking-level difference in the irrelevant speech effect (ISE). In Experiment 1 the detrimental effects of irrelevant sound on serial recall were found to be the same whether the material (speech or music) was presented at a high (75 dB[A]) or low (60 dB[A]) overall level. In Experiment 2, adding pink noise to the speech signal produced a linear improvement in performance with decreasing speech-to-noise ratios. In Experiment 3 the contribution of binaural unmasking to the ISE was found to be negligible. The results (a) confirm that the segmented, changing nature of the irrelevant sound is crucial in producing the ISE and (b) suggest that the adverse effects of disruptive auditory input may be alleviated by introducing additional uniform masking noise.

Individual differences in susceptibility to the "irrelevant speech effect".

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.

Additivity of loudness across critical bands: a critical test.

The use of magnitude estimation as well as axiomatic measurement theory has led to the suggestion that loudness adds across critical bands. In the present paper, we challenge this postulate by applying a more sensitive methodology, based on Falmagne's (1976) random conjoint measurement procedure. A necessary condition for additivity of loudness was investigated in tone complexes consisting of 2-kHz and 5-kHz (resp. 3-kHz) components; the results showed systematic deviations from additivity. We argue that these deviations are due to asymmetric masking of the higher component by the lower one, and we propose a tentative quantitative model to account for the data. Such a model is in line with results from tone-on-tone masking, which show masking to be effective over a range of several critical bands.

On the "absoluteness" of category and magnitude scales of pain.

The concept of "absolute scaling" (Zwislocki & Goodman, 1980) implies that direct judgments of sensory magnitude not only reflect the relative positions of the stimuli being judged, but also permit us to assess level differences in sensation. In order to explore this notion for different scaling methods, in the present investigation we compared magnitude estimation with category partitioning, a verbally anchored categorization procedure, in scaling painful pressure stimuli covering different intensity ranges. The results indicate that when the same stimulus range was presented after 1 week, both methods appeared to be highly reliable, with category partitioning faring somewhat better than magnitude estimation. When the stimulus range was unobtrusively changed between sessions, both methods reflected the within-subjects shift in absolute level. When two different sets of subjects judged the slightly different stimulus ranges, both methods resulted in scale values consistent with absolute scaling, though only category partitioning was sensitive enough to differentiate the two stimulus ranges. The results are discussed in the context of different possibilities of anchoring direct scaling methods in order to obtain "absolute" level information.

An investigation of the facilitation of simple auditory reaction time by predictable background stimuli.

Two experiments explored a surprising result reported by Emmerich, Pitchford, and Becker (1976): Simple reaction time (RT) to an auditory stimulus can be facilitated by the presence of a tonal background (or masker). In the first experiment, simple RT to a tonal signal was investigated for a variety of background frequencies and loudness levels, and significant facilitation of RT was found for low levels of the background. In the second experiment, no evidence of facilitation was found when the background stimulus was a randomly varying narrow-band noise, although evidence for facilitation was again found with a constant tonal background.