TECHNICAL NOTES AND RESEARCH BRIEFS

more points on the psychometric function and thereby obtain relatively precise esti- mates of both the location and spread of the function. This application of the pro- grammer is illustrated in the following example. It was required to measure both the threshold and difference threshold of a

250 Hz tone using the YES-NO procedure, i.e., the subject was required to state whether or not the tone was audible. In

this case the midpoint of the psychometric function is defined as the "threshold"; and the standard deviation of the function is defined as the "difference threshold." Little was known about the location of the

ps.vchometric function, but its standard de- viation was expected to be on the order of 1 dB.

Each channel was programmed to follow the simple UP-DOWN strateg3, for the first two runs using a relatively large step size of 2 dB. This was done in order to converge rapidly on the region of interest. For the next ten runs in each channel a strategy of the UDTR type with a step size of 1 dB was used. The 70.7% point was estimated in Channel I, and the 29.3% point was estimated in Channel II. The mean of the

estimated 70.7% and 29.3% points pro- vides an estimate of the threshold (assum- ing a symmetrical psychometric function). The difference between the 70.7% and 29.3% points provides an estimate of the

difference threshold. If the psychometric function is a cumulative normal with

standard deviation •, then the difference between these two points is 1.09 a.

Each of the required strategies was pro- grammed in the appropriate subunit of the sequential-logic unit (see Fig. 2). Two subunits were used in each channel; Sub- unit 1 for the simple UP-DOWN strategy, Subunit 2 for the UDTR strateg3,. Each subunit was of the form shown in Fig. 1. For the simple UP-DOWN strategy, the value of n (i.e., the number of pulses which can be stored), in both response stores was zero. For the UDTR 70.7% procedure the values of n for the positive and negative response stores were 1 and 0, respectively. Conversely, for the UDTR 29.3% pro- cedure the values of n were 0 and 1, respectively.

Presentations for the two channels were

interleaved at random. As a result, the re- quired number of runs per test were not completed simultaneously in both channels; the required twelve runs were completed in Channel II slightly ahead of Channel I. The records obtained in the experiment are shown in Fig. 3. The upper half of the figure records the value of the stimulus- level store in Channel I; the lower half of the figure records the level in Channel II. The end of each run is indicated by an arrow. The mean of every second run

(omitting the first two) is used as an estimate of the appropriate percentage point; the 70.7% point for Channel I, the 29.3% point for Channel II. The resulting estimates are tabulated at the bottom of

the figure. The data show that although the threshold appeared to drift slightly during the test, the difference threshold appeared to remain relatively stable.•-•

1. Anderson, T. W., McCarthy, P. J. and Tukey, J. W. 1946 "Staircase Methods of Sensitivity Testing," KAVORD rept. 65-46, 21 Mar.

2. Campbell, R. A. 1963 "Detection of a noise signal of varying duration," J. Acoust. Soc. Am. 35, 1732 (See Appendix).

3. Cardozo, B. L. 1962 "Een sequente keuze methode voor her bepalen van psychofysische drempelwaarden," Verslag No. 22, Instituut voor Perceptie Onderzoek, Eindhoven, Holland.

4. Dixon, W. J. and Mood, A.M. 1948 "A Method for Obtaining and Analyzing Sensi- tivity Data," J. Am. Statist. Assoc. 43, 109.

5. Robbins, H. and Monro, S. 1951 "A Stochastic Approximation Method," Ann. Math. Statist. 22, 400.

6. Taylor, M. M. and Creelman, C. D. 1965 "In- troduction to the PEST Psychophysical Pro- cedure," personal communication.

7. Wald, A. W. 1947 Sequential Analysis (John Wiley & Sons, New York).

8. Wetherill, G. B. and Levitt, H. 1965 "Sequen- tial Estimation of Points on a Psychometric Function," Brit. J. Math. and Statist. Psychol. 18, 1-8.

9. Zwislocki, J., Maire, F., Feldman, A. S. and Rubin, H. 1958 "On the Effect of Practice and Rubin, H. 1958 "On the Effect of Practice and Motivation on the Threshold of Audibility," J. Acoust. Soc. Am. 30, 254-262. See Experi- ment V.

INEXPENSIVE NEW SOUND-LEVEL CALIBRATOR

THE NEW GENERAL RADIO Type 1562-A Sound-Levd Calibrator is a compact, self- contained unit for making field calibrations on microphones and other sound-measuring instruments. It generates five USASI-pre- ferred frequencies (125, 250, 500, 1000,and 2000 Hz, =t=3%) at an accurately known

sound-pressure level of 114 dB (re 20 t•N/m•'). Level accuracy with the Western Electric 640AA or equivalent microphone is =t=0.3 dB at 500 Hz and =t=0.5 dB at other

frequencies. Directly or with the adaptors supplied, the 1562-A will calibrate many common types of microphones and asso- ciated sound equipment. An electrical out- put of 1 V is provided for tests on instru- ments without microphones.•-•

WASHER NOISY? MAYBE YOU'RE

JUST WELL EDUCATED

THE MORE EDUCATION yOU have, the more you may be bothered by noise from house- hold appliances.

Researchers at the Acoustics and Seismics

Laboratory of The University of Michigan's Institute of Science and Technology have probed the reactions of 192 persons to appliance noise.

The laboratory reports that "there appears to be a strong trend toward bother- someness increasing with educational levels. There can be little doubt that college- educated individuals are more bothered

with the sound stimuli presented than the remainder of the population."

Results of the tests in the living room of a normally furnished Ann Arbor home also indicated that completion of high school might not be a factor.

"Those who completed high school, in fact, seemed slightly less bothered than those who attended high school but re- ceived no diploma," according to the report.

In the carefully controlled experiment, the researchers also found that those who

were most bothered by the noise, although they were college graduates, did not neces- sarily have high incomes.

Many respondents were low-income graduate students at The University of Michigan. Thus, the report continues, "in the present case it is possible to state with a rare degree of confidence that it is educa- tion and not income which is contributing

importantly to the relationship" between noise and bother.

The researchers also discovered that

persons with many appliances in their kitchen are less bothered when the sounds

are at low levels. "At higher levels, how- ever, there is a tendency for this same group of people to be more bothered."

The participants in the experiment re- sponded to 150 appliancelike acoustical stimuli and a variety of questions relating to appliance noise in home environment.

The research was conducted by a team of U-M faculty members including Norman E. Barnett, research physicist; Bruce E. Erickson, associate professor of architec- ture; and Robert Hefner, associate pro- fessor of psychology.•-•

The Journal of the Acoustical Society of America 013

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