The results of the two experiments lead to the following conclusions:

1.Moving spatial sound sensations were always more annoying than fixed sound localization under the condition of a constant SPL. The annoyance increased with a greater fluctuation rate of the IACC as well as the τIACC.

2.Fluctuations of the IACC and the SPL independently contribute to the scale value of annoyance.

3.Fluctuations of the τIACC and the SPL independently contribute to the scale value of annoyance.

4.The contribution of fluctuations in τIACC to annoyance was greater than that of the IACC when the range of the SPL was from 65 to 75 dBA.

Therefore, in order to describe subjective evaluations of moving noise sources, we should make binaural measurements to obtain both the spatial factor extracted from the IACF and the temporal factor extracted from the ACF.

11.3 Effects of Noise and Music on Children

We sought to understand the differential effects of noise and music on the performance of mental tasks by children. Under conditions of quiet (no stimulus), noise, and music, children carried out cognitive tasks that are thought to lateralized in one hemisphere or the other (Table 11.5). The tasks either involved addition (left hemisphere specialized) or pattern search (right hemisphere specialized).

Tests were carried out in classrooms (the reverberation time 0.5–0.9 s in the 500Hz octave band) of two schools in a quiet living area (Ando et al., 1975; Ando and Kang, 1987; Ando, 1988). The total number of subjects participated in the experiments was 559 (Table 11.5). The no-stimulus, quiet condition was tested in a normal classroom without any reproduced sound. The noise group was tested while being exposed to jet plane noise of 95 ± 5 dBA, peak. The music group was tested while listening to an excerpt of music from the fourth movement of Beethoven’s Ninth Symphony (85 ± 5 dBA, peak). As shown in Fig. 11.12, the time pattern of the

Table 11.5 Number of subjects monitored while performing two different metal tasks

Fig. 11.12 Sound-pressure levels of stimuli reproduced in classrooms as a function of time. Left: Aircraft noise adjusted by a peak of 90 dBA in this figure. Right: Music piece before the chorus of Beethoven’s Ninth Symphony adjusted by a peak of 90 dBA

music was similar to that of the jet noise. The spectra of the two sound signals were similar also (Ando et al., 1975). Music and aircraft noise were reproduced from two loudspeakers set at the front of the classroom, during every alternative period during the addition and search tasks given by

where n = 1, 2, . . ., 7 for the adding task, and n = 1, 2, . . ., 5 for the search task. Examples of one task period are shown in the upper part of Fig. 11.13 (60 s/period)

Fig. 11.13 Proportion of V-type relaxed children during the adding task (left-hemispheric task) without any stimuli, with aircraft noise stimulus reproduced and music stimulus reproduced. The upper part indicates the task of one period (60 s) in

N = 15

Fig. 11.14 Proportion of V-type relaxed children during the search task (right-hemispheric task) without any stimuli, with aircraft noise stimulus reproduced and music stimulus reproduced. The upper part indicates the task of one period (30 s) in

N = 10

and Fig. 11.14 (30 s/period). The individual work produced in each period, called the “working curve,” was drawn for all test results. The mean work performance is not discussed here, because there were no significant differences between the different conditions. Of particular importance in evaluating the tests results is the “V-type relaxation.” This score is classified into two categories according to the occurrence of a sudden large fall in the working curve during each task. This is assessed by Mi < M – (3/2)W, i = 1, 2, . . ., N, where M is the mean work performance and W is the average variation of the curve excluding an initial effect at the first period, i = 1. Such relaxation is thought to be caused by an abandonment of effort when mental functions are disturbed.

As shown in Fig. 11.13, the percentage of V-type relaxed children given the additional task (N = 15) was much greater in the music group than in either the no-stimulus group or the noise group (p < 0.01). As shown in Fig. 11.14 for patternsearch task (N = 10), the percentage of relaxed children was similar under all test conditions, except for a slight increase in the noise group. The results of the mental tasks were not dependent on the sex, birth order, or birth weight of a child or on whether or not the mother was a working mother (Ando et al., 1975).

Significant differences in the factors τ1 and τe extracted from the running ACF of the noise and the music as a function of time may be found in measured results

Differences in interference effects occurring during left and right hemispheric tasks, respectively, may be well described in terms of the temporal factors extracted from ACF and the spatial factors extracted from IACF as listed in Table 11.6. On the other hand, annoyance may be described by all of these factors.

Table 11.6 Effects of noise on two difference tasks and annoyance, in relation to the temporal and spatial factors extracted from the ACF and the IACF, respectively

X: Factors may influence the corresponding task, and annoyance. LL = 10 log [ (0)/ (0)ref], where (0) = [ ll(0) rr(0)]1/2.