Evening star., 1938-06-04
STARS, MEN AND ATOMS
Notebook of Science Progress in Field,
Laboratory and Study.
L Laboratory ana study
BY THOMAS r. HENRY.

The familiar that's my bad ear" prob
ably has little justification.
In the vast majority of cases If one
ear is defective the other is equally de-
fective and If one ear is normal the
other is normal, according to a survey
just reported by the Public Health Serv-
ice. The purpose of this survey was to
set up hearing standard" for the
American people based on the actual
auditory sensitivity of vast numbers Of
people. 1t constitutes the first scientific
effort to measure the hearing of rep
resentative group of the general popula-
ton with precision instruments.
It was conducted, in cooperation with
a group of prominent ear specialists and
physicists of the Bell Telephone labora-
tories in IL cities, as part of the ma
tional health survey. The cities were
Birmingham and Montgomery, Ala;
Atlanta and Brunswick, Ca; New Or
leans, Detroit, st. Paul, Brooklyn, and
Amarillo Dallas and Houston, Tex. APP
proximately 5000 persons who had been
canvassed by the health survey in those
cities were invited to have an audio-
metric test of their hearing and medi-
ranged in age from 8 to 80 years and
was about equally divided as to sex.
About half had reported that they were
partly or wholly deaf, and the other half
that they had normal hearing.
Previously, according to the Public
Health Service report, there have been
no statistics for the population at large.
A good many States have conducted such
tests for school children. There have
been studies in hospitals, clinics and in
stitutions for the deaf and census re-
ports on the numbers OF deaf mutes.
Conclusions based on such figures were
apt to be one-sided, since they obviously
were confined to non-representative
groups of the population. It was not
possible to measure the hearing of any
particular individual against the norm
of hearing for the general population of
the same age and sex. On the basis of
the tests it is expected that a national
standard will be set up. The medical
examinations were made in each city by
local physicians specializing in diseases
of the ear.
The tests were made with an instru-
ment known as the IA audiometer. This
generates pure tones at eight different
frequencies, ranging from very low to
very high pitch. It also has an inten-
sity scale, which Is used to determine the
intensity Of the tone generated. This
intensity is recorded on a dial similar
to radio dial. BY adjusting the con-
trolls, the intensity can be varied by
known amounts, from value too low to
be detected by the human ear to an ex-
tremely loud level.
The response Of person in sound
insulated booth to different tones meas
ures the intensity value of his hearing.
The hearing level is calculated from the
weakest intensities at which the person
can hear the eight pitches generated by
the audiometer. The tones generated by
the audiometer are the most important
in social munication-speech and
music The graph picture Of hearing OBJ
tanned from the audiometer shows how
much hearing loss a person suffers. This
loss is measured In terms Of decibels,
the usual unit for measuring the loud
ness of sounds.
In the present study it was found that
persons with normal hearing may have
a loss of from one to five units. Persons
who have difficulty in understanding
speech from the platform of public
auditorium have a hearing loss of from
20 to Is units. II a person cannot UNDER
stand speech from 2 tb, 3 feet directly