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Lymz E. Miner
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Michigan State
University.

 

ABSTRACT
EFFECTS OF AUDITORY FREQUENCY AND
MANNER OF PRESENTATION OF SIGNALS

ON JUDGMENT OF DISTANCE BY
BLIND INDIVIDUALS

by Lynn E. Miner

This study is concerned with the auditory skills
of blind individuals. The purpose of this thesis was to
analyze the effect of auditory frequency and manner of
presentation of signals on the judgment of distance by
blind individuals. Three primary variables were investi-
gated in this study; They were auditory frequency,
distance from a sound source, and presentation of the
auditory stimulus.

Thirty-six visually handicapped students from the
Michigan School for the Blind participated in this experi-
ment. Each subject was presented a certain set of
conditions at a distance of ten feet from the sound source
in the test room. Next, he was disoriented in the test
room and repositioned at another predetermined distance.
He was then instructed to walk forward until he again
perceived his distance from the sound source as ten feet.
The varying conditions for the subjects were auditory
frequency, distance from the sound source, and manner of
presentation (continuous vs. intermittent) of the auditory

stimulus.

Lynn E. Miner

The error judgment in perceived distance for each
subject was measured and recorded. An analysis of variance
was computed to determine the significance of differences
between mean scores.

No statistically significant results were obtained.
None of the F ratios were significant at the .05 level of
confidence. The interactions between these variables were
computed and found to be nonsignificant at the .05 level
of confidence. The major findings of this study do not
indicate that auditory frequency, distance from the sound
source, and the manner of presentation of the auditory
stimulus are significant variables affecting the perception

of distance from the sound source by the blind.

 

EFFECTS OF AUDITORY FREQUENCY AND
MANNER OF PRESENTATION OF SIGNALS
ON JUDGMENT OF DISTANCE BY
BLIND INDIVIDUALS

By

Lynn E. Miner

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF ARTS

Department of Speech

1963

DEDICATION

Dedicated -- not to a person but
to a profession which is devoted
to serving people. May we never
lose sight of our goal.

ii

ACKNOWLEDGEMENTS

The writer wishes to express his profound
appreciation to those who have given advice and
guidance in the preparation of this thesis.

Gratitude and reCOgnition are extended to
Dr. James W. Hillis for his diligent direction
of this thesis. Acknowledgement is extended to
Dr. Herbert J. Oyer who constantly motivated and
inspired the author to broaden his understanding
and appreciation of our professional field.

The writer is conscious of his obligation to the
administration, faculty, and students at the
Michigan School for the Blind who directly or
indirectly have been a professional influence.
The author wishes to thank Mrs. Deirdre Circle
for meticulously editing and typing the trial
and final editions of this thesis. Finally, the
writer is thankful to his parents for providing
him with a philosophy of education based on
insight and wisdom.

iii

TABLE OF CONTENTS
Chapter Page

I STATEMENT OF THE PROBLEM .
Introduction . . .
Statement of the Problem
Definitions. . . .
Questions Posed at Outset.

II REVIEW OF THE LITERATURE . . . . . . . . . . .

III SUBJECTS, EQUIPMENT, AND PROCEDURES
SubJeCtS O O 0 O O O O O O O O 0
Equipment. . . . . . . . . . . .
Procedures . . . . . . . . . . .

O O O O
O O O O
O O O O
O O O O
O O O O
O O O O
d—L—L—L

IV RESULTS AND DISCUSSION . . . . . . . . . . . .
Results. 0 o o o o o o o o o o o o o o o o' 0
Discussion . . . . . . . . . . . . . . . . .

—‘\O\O O\O\U‘lU1 x] Ul-P'J-‘d‘

Mud—L

V SUMMARY AND CONCLUSIONS. . . . . .
summary 0 O O O O O O O 0 O O O 0
Conclusions. . . . .
Implications for future research

0 O O O
[UNIUIU
CDCDU'IU'I

BIBLIOGRAPHY 0 0 O O O O O 0 O o O O O O O O O 0 O 0

K)!
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APPENDICES O O 0 O O O O o O O O O O 0 O O I O 0 O O

KN
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iv

LIST OF TABLES
Table Page
1 ANALYSIS OF VARIANCE. . . . . . . . . . . . . . 20
2 SOUND PRESSURE LEVELS IN TEST ROOM. . . . . . . 23

CHAPTER I
STATEMENT OF THE PROBLEM

Introduction
Our senses keep us informed of the happenings in

our environment. These senses, especially the distance
senses of sight and hearing, help us orient to our
surroundings. Individuals with diminished visual acuity
are, of necessity, forced to rely on audition in gaining
information about their environment.

Through hearing, a blind person can learn to evaluate

personality. . . . Through changes in pitch, rhythm,

and quality of tone he can note the various moods

corresponding to the gamut of the emotions. How well

he is able to associate the various aspects of the

human voice with the emotions will depend upon his

intelligence intuition and experience in contact

with people.1

Blindness imposes certain basic limitations on the

blind individual. Each limitation necessitates definite
adjustments in the learning process for the visually
handicapped. First, blindness places restrictions in the
range and variety of experiences in which the individual
may partake. The visual and tactual senses experience
considerable limitations. Second, blindness imposes

restrictions in the control of the environment and the

self-concept in relation to the environment. Vision gives

 

1Carl Weiss, "Reality Aspects of Blindness As They
Affect Case Work," The Family, (February, 1946), p. 12.

us a great deal of control over our environment. Finally,
blindness imposes restrictions on mobility and orientation.
This is probably the most serious of all restrictions and
the one with which this thesis is most directly concerned.
The blind child cannot change his immediate environment;
he is dependent on the assistance of others. This depend-
ence could affect his social relationships and lead to
self debasement.1

The role of auditory skills in mobility and orien-
tation is immensely important. Unfortunately, however, as

Rusalem suggests,

In the area of mobility, we have largely been playing
by ear. We have been aware that certain procedures
work better than others and that blind persons differ
in their ability to use various travel techniques.
However, we have lacked the basic orientation which
might make our work scientific and which would hasten
the day when most blind persons could travel independ-
ently. It would be argued that even our present
knowledge is not being effectively dissemenated, and
that is probably true.2

Rusalem adds that the

. . . loss of the ability to get about has been a
crucial problem in the rehabilitation of the blind.
Frequently, the success of a variety of the social
and vocational services depends upon preliminary
success in teaching independent travel. Lack of
mobility can isolate a blind person from his environ-
ment.

 

1Paul A. Zahl, Blindness, (Princeton, New Jersey:
Princeton University Press, 1950), p. 92.

2Herbert Rusalem, "Research in Review," New Outlook
for the Blind, LII, No. 8 (1958), p.-313, .

3Ibid.

He goes on to limit the problem as follows: "The
nub of the problem is that there is sufficient auditory
information in the environment if the crucial properties
of the sound field could be perceived and recognized."1

Lowenfeld described the problem similarly when he
stated:

The most important factor in increasing the blind
child's ability to gain experiences is his own ability
to get about and secure stimulation by himself. How
to learn his way in familiar and unfamiliar surround-
ings is a never-ending task that begins with the blind
child's first steps.2

One auditory skill essential to effective mobility
and orientation is mastery of sound localization. Sound
localization is the process of determining the distance
and direction of an acoustic stimulus. Three coordinates
are fundamental to this ability: a judgment of distance and
the interaction of two angles. A majority of existing
studies have concentrated on the determination of the
direction of the acoustic stimulus. Other studies relative
to sound localization are comparative studies which deal
with differences among the blind and sighted. The orien-
tation of this thesis is toward the role of distance,

auditory frequency and pulsation in sound localization.

 

1Ibid.

 

2Berthold Lowenfeld Our Blind Children (Springfield
Ill.: Charles C. Thomas Pub., 195677Ip. 1 . , ’

Statement of the Problem

For the blind individual to become mobile, he must
learn to take advantage of available sensory clues. This
includes mastery of certain basic auditory skills. The
purpose of this research is to investigate the effects of
auditory frequency and manner of presentation of signals
on judgment of distance by blind individuals. The scope
of this thesis is restricted to the above mentioned auditory

signals.

Definitions
The following terms are defined for clarification
in this study:
Auditory frequency.--The three frequencies explored

are 500, 2000, and 8000 cycles per second.

Manner of presentation.--Both continuous and inter-

mittent tones were utilized.

Judgment of distance.--The individuals conception
of the space between himself and the source of the auditory
stimulus. In this instance each person was asked to make
a judgment of ten feet between himself and the source of

the stimulus.

Blind individuals.--Thirty-six braille students at
the Michigan School for the Blind. Most of the participants
were totally blind. Students with light perception utilized

blindfolds.

Two other terms, while not directly involved in this
study, need definition. The terms are frequently employed
when referring to the rehabilitation of the blind.

Mobility.--The term used to denote the ability to
navigate from one's present fixed position to one's desired

position in another part of the environment.1

Orientation.--The process of utilizing the remaining
senses in establishing one's position and relationship to

all other significant objects in one's environment.2

Questions Posed at Outset
Questions posed at the outset of this study were:

1. Do certain auditory frequencies allow for a more
accurate judgment of distance than other auditory
frequencies?

2. How does initial distance from a sound source affect
the blind individual's perception of another predeter-
mined distance?

3. Which type of presentation allows for a more accurate

judgment of distance: a continuous or intermittent tone?

4. Is there a dependence of presentation (continuous vs.

 

1"Orientation and Mobility Terms" (American
Association of Instructors of the Blind, St. Louis, Mo.,
March, 1962), p. l. (Mimeographed.)

21bid.

O\

intermittent) on distance from the sound source in the

auditory perception of a distance of ten feet?

Is there a dependence of auditory frequency on initial

distance from a sound source in the auditory perception
of a distance of ten feet?

Is there a dependence of auditory frequency on presen-

tation (continuous vs. intermittent) in the auditory

perception of a distance of ten feet?

CHAPTER II
REVIEW OF THE LITERATURE

In the area of mobility and orientation of the
blind, little systematic information is available regarding
the function of auditory sensations. The bulk of available
information consists of comparative studies contrasting the
blind and sighted on auditory performance tasks. Most of
these studies are concerned with sound localization.

One of the few studies dealing with the role of pitch
was conducted by Cotzin and Dallenbach. They investigated
the function of pitch in the perception of obstacles by the
blind. This phenomenon is sometimes referred to as "facial
vision." As a result of their investigation, they indicated
that "aural stimulation by reflections from the obstacles
is both a necessary and sufficient condition for object
perception." They concluded further that "changes in pitch
are the basic clues of the perception of obstacles by the
blind, and that they do not occur unless the higher partials,
approximately 10,000 cps and above, are present in the
stimulus sounds."1

Supa joined forces with the above authors in an

 

1M. Cotzin and K. M. Dallenbach, "Facial Vision:
The Role of Pitch and Loudness in the Perception of
Obstacles b the Blind," Amegican Journalgof Psychology,
LXIII (1950 , p. 512.

earlier study of obstacle perception by the blind. Their
study was exhaustive in nature and represented an important
contribution to the final solution of this problem. Seven
experiments were conducted, three preliminary experiments
and four main experiments. The preliminary experiments
were exploratory and normative. Blind and sighted subjects,
all with blindfolds over their eyes, were placed at various
distances in front of either a wall or a portable masonite
board. They were asked to walk toward the obstacle and
(1) indicate their first perception of it and (2) to approach
it as closely as possible without touching it. In each of
the preliminary experiments, twenty-five trials were
obtained from each subject. The average distance and mean
variation of the subject's first perception and final
appraisal were computed for the statistical data of tables.
In the first experiment the end wall of a large hall was
the obstacle and the starting point of the subject varied.
In the second experiment the screen was the obstacle and
its position was varied; the subjects started from a fixed
point. In the third experiment the position of both the
subject and the screen was varied. The authors found that
while the blind in this study possessed a high degree of
ability to perceive obstacles at a distance, the sighted
could easily acquire this ability with practice.

The purpose of the four main experiments by Supa,

Cotzin, and Dallenbach was to control certain sensory cues.

The first main experiment was conducted in order to determine
whether pressure sensations aroused by reflected air waves
were necessary to the perception of obstacles. The second
main experiment was designed to ascertain whether or not
aural stimulation by reflected sound waves was a necessary
condition for the perception of obstacles. In the third
main experiment the exposed areas of the skin were left
open to air and sound waves but all auditory stimuli were
drowned out by a masking sound conducted to a set of head-
phones worn over the ears of the subject. In the fourth
main experiment each subject was placed in a sound proof
room with high-fidelity headphones over his ears through
which he could listen to the sounds of the experimenter
who, carrying a microphone, walked in another room towards
the obstacle. All subjects were able to report first
perceptions and final appraisals in this experiment where
only ear stimulation could play a role. Their most general,
relevant conclusion to be noted here was that "aural
stimulation is both a necessary and sufficient condition
for the perception of obstacles."1

Fletcher investigated the accuracy with which blind-
folded subjects could localize the distance of sound sources.
Three main variables were studied. They included the dis-

tance of the sound source from the subjects, the frequency

 

1M. Supa, M. Cotzin, and K. M. Dallenbach, "Facial
Vision: The Perception of Obstacles by the Blind,".Amer;can
Journal of Psychology, LVII (April, 1944), p. 183.

10

of the sound source, and the audible angle at the subjects.
His findings indicated that the subjects could localize the
distance of sound sources with more than chance accuracy.
Distance was the only significant variable.1
A study by McCarty and Worchel makes reference to

the possibility of a mechanism similar to the one used by
bats in their environmental orientation.

It is known that bats use a type of vocal radar to

guide them in utter darkness, and thus it would seem

that a similar mechanism is at work in humans; but if

an object is closer than fifty feet the echo and

original sound blend to such an extent that they can-

not be heard separately by the human ear.

Work by Cotzin and Dallenbach, however, indicated
that rather than being the pure echo, it was a dif-
ference in tone between the original sound and the
echo. This is known as the Doppler Shift, and it is
the same as the often observed difference in the sound
of a car as it approaches and then recedes."

In other words, the blind perceive objects when they hear

a rise in pitch of the echo (Doppler Shift). This difference

in frequency with its relative intensity and manner of

presentation tells them where the obstacle is located.
Griffin has investigated some of the variables in

sound localization. He stated that a thermal noise (100

through 12,000 cps) was more effective in detecting an

obstacle than were pure tones. He also noted that pure

 

1John L. Fletcher, "Localization of Sounds in Depth,"
U. S. A. Medical Research Laboratory Report, MXMLVII, .
NO. 302 ll (1957), P. 1E.

2M. McCarty and P. Worchel, "Rate of Motion and
Object Perception in the Blind," New Outlook for the Blind,
XLVIII (November, 1954), p. 315.

11

tones of 10,000 cps and higher provided for more accurate
detection of obstacles than the frequencies 125-8000.1
One of Griffins' studies dealt with the acoustical
orientation of the oil bird, steatornis. He made an
acoustic analysis of the sound emitted by this bird while
flying about in a totally dark cave. By emitting sounds
the bird was able to avoid obstacles while in flight. The
most appreciable components of the emitted sounds were
between 6000 and 10,000 cps. The average frequency was
7000 cps; the duration of each sound was about one msec.
with intervals between sounds averaging 2.6 msec. When the
ears of the bird were plugged, they lost theirwebholocation
ability.2
An investigation into the function of auditory

frequencies in sound localization was authored by Fedderson,
Jeffres, Sandel and Teas. They stated:

We may conclude that the localization of high frequency

pure tones, where there is no cue provided by the onset

of the tone, demands a difference of level at the two

ears which can be provided only by tones above 5000 cps.

At the lower frequencies where diffraction around the

head is less and the differences of level, therefore,

smaller, the subject consistently underestimates the

azimuth angle. This underestimation decreases with
increasing frequency and increases with increasing

A__A._
1%

1Donald R. Griffin, Listenin in the Dark, New Haven:
Yale University Press, 1958), p. 308.
2Donald R. Griffin, "Acoustic Orientation in the 011

Bird, Steatornis," National Academy of Sciences, XXXIX,
No. 8 (1953), PD. 88 ~93.

12
azimuth angle.1
One of the parameters of the present study is
concerned with the presentation of the stimulus. Both
continuous and interrupted tones are utilized. Zwislocki,
Hellman, and Verillo conducted a study in this regard. It
was their impression that
Neural responses to pulses seem to be more easily
detected and quantified than responses to other
sound stimuli. Consequently, in the search for physio-
logical correlates of certain characteristics of
psychophysical responsesé pulse stimuli appear
particularly attractive.
von Bakesy has written of the spatial attributes
of sounds. He stated:
Perception of the distance of a sound depends upon
characteristics of the sound field that still are not
well understood, but in the experimental situation the
apparent distance was determined simply by loudness.
The less the loudness, the farther away from the head
the sound image seemed to be, and when the loudness
remained constant this distance was always the same.3
The ratio of the direct sound to the reverberant
sound intensity has been suggested by Fletcher as a factor
influencing depth localization. He specified that
. . . either a reduction in loudness or a decrease in

ratio of direct to reverberant sound intensity, or both,
cause the sound to appear to move away from the observer.

 

1W. E. Fedderson et al., "Localization of High
Frequency Tones," Journal of the Acoustical Societ of
America, XXIX (September, 1957), pp. 399-91.

2J. Zwislocki, R. P. Hellman, and R. T. Verillo,
"Threshold of Audibility for Short Pulses," Journal of

the AcousticalfSociet of America, XXIV, No. 10 (1962),
pp. 162+8‘520

3Georg von Bakesy, Ex eriments in Hearin , (New York:
NcGraw-Hill Co., Inc., 1960), p. 280.

13

. . .It has not been found possible to put these
relationships on a quantitative basis. Probably a
given loudness change, or a given change in ratio of
direct to reverberant sound intensity, causes dif-
ferent sensations of depth depending upon the character
of the reproduced sound and upon the observer's
familiarity with the acoustic conditions surrounding
the reproduction. Since the depth localization is
inaccurate even when listening directly, it is
difficult to obtain sufficiently accurate data to be
of much use in a quantitative way. Because of this
inaccuracy, good auditory perspective may be obtained
with reproduced sounds even though the properties
controlling depth localization depart materially from
those of the original sound.1

The auditory skills of blinded individuals training
with pilot dogs were investigated by O'Neill, Oyer, and
Baker. The purpose of their study was to determine whether
a significant relationship existed between the ability of
blinded individuals to use a pilot dog successfully and
their hearing acuity, hearing discrimination, and sound
localization ability. Fifty-three subjects were admin-
istered a battery of tests which included the following:
(1) pure tone threshold tests, (2) sound discrimination
tests, and (3) sound localization tests. The trainees under
study were evaluated for each subject's relative skill in
the use of a pilot dog by trainers employed in the Pilot
Dog training program. The results suggested that auditory
acuity and the ability to localize sound may determine

 

1Harvey Fletcher, Speech and Hearing in Communi-
cation, (Princeton, New Jersey: D. Van Nostrand Co., Inc.,
1953), PP. 221-22.

14

proficiency in the use of a pilot dog by a blinded person.1

In summary, the literature contains several studies
which are related to this thesis. It suggests that the
higher auditory frequencies should allow for the greatest
accuracy in the judgment of distance from a sound source.
The main variables affecting the auditory perception of the
distance of a sound source include auditory frequency, the
distance from the sound source, the manner of presentation
of the auditory stimulus, the intensity of the auditory
stimulus, and the acoustical characteristics of the environ-

ment.

 

1John O'Neill, Herbert Oyer, and Donald Baker,
"Auditory Skills of Blinded Individuals Training With

Pilot Dogs," Journal of S eech and Hearin Research, I,
No. 3 (September, 1958), pp. 262-67.

CHAPTER III

SUBJECTS, EQUIPMENT AND PROCEDURES

Subjects
The subjects for this study were thirty-six high school

students at the Michigan School for the Blind. Nineteen
boys and seventeen girls participated in the study. All
subjects were required to pass a pure tone hearing test at
a ten-decibel level for each ear. The following frequencies
were employed: 500, 1000, 2000, 4000, and 8000 cps.

All students had been examined by an ophthalmologist
and declared legally blind prior to their admission to the
school. All of the students were totally blind. The few
who had light perception were blindfolded before being
exposed to the testing situation.

All except three of the thirty-six subjects had lost
their visual acuity before the age of two. Most of the
subjects had been blind since birth; retrolental fibroplasia
was the major cause for the visual losses as indicated by
the ophthalmological reports. The three remaining subjects
had lost their vision at age three, five and sixteen respec-
tively.

Only students with average or above average intel-
ligence as determined by school achievement were utilized.

All subjects were randomly selected within the visual,

15

16

auditory and intellectual restrictions mentioned.

Equipment

The experiment was conducted in a room which had
been partially treated with acoustical tile. A table
indicating the acoustical specifications of the room is
found in Appendix A. These specifications were computed
by the Building Division of the State of Michigan.

Pure-tone signals were generated for the experiment
by a Maico Audiometer, model H1-B. The pure tones were
directed from the audiometer through a six inch speaker,
type #6 CM-47 manufactured by the Oxford Electrical Cor-
poration. The three pure tones presented were 500 cps,

2000 cps, and 8000 cps.

Procedures
Prior to the experiment each student had satis-
factorily passed a pure-tone screening test at ten decibels
in each ear for the frequencies previously mentioned. The
following instructions were read to the subjects before the
experiment began:

In just a moment you will be asked to listen closely

to a particular tone. You will be exactly ten feet
from that tone. Next you will be taken back a greater
distance from that tone and asked to walk forward

until you again think you are ten feet from that tone.

A guide rope is provided as an aid in walking a straight
line. Remember: walk forward until you are ten feet
from the tone. Once you have estimated the correct
distance, remain standing still until further
instructions are given. Do you have any questions?

The speaker was positioned one foot from a wall and

17

five feet above the floor. A fifty-five foot guide rope

was fastened between the speaker and a pole. The speaker
was positioned at the approximate head level of the subjects
and pointed toward the head of each subject.

Afterthe subject had the opportunity to hear the
stimulus at exactly ten feet from the sound, an irregular
path was followed, thus attempting to disorient the indi-
vidual. One of three different starting distances was
employed for each subject. Subjects were positioned at
either 26 feet, 38 feet, or 50 feet from the auditory
signal. One of two types of auditory signals (continuous
vs. intermittent) was presented to each subject. The
intermittent tones were manually pulsed every .5 second
for a .5 second duration.

The table in Appendix B indicates the intensity of
the stimuli presented. The intensity was presented at
50 decibels above audiometric zero. Audiometric zero for
each frequency was ascertained by determining the threshold
tested at a distance of three feet from the sound source.
This procedure was conducted in the sound field of the
actual test room on a pair of normal ears.

Once the subject had completed his estimate of ten
feet, his judgment error was measured. The judgment error
was the distance between the exact ten foot mark and the
heels of the subject. The error was recorded in inches and

employed as the basic measure or score in the experiment.

18

Three fundamental conditions were explored in this
experiment. There were several levels for each condition.
Each combination of conditions, or events, was presented
to two randomly selected subjects from the sample of thirty-
six. The table in Appendix C indicates the specific combi-
nations of events presented to each subject.

The first condition examined was auditory frequency.
Three different auditory frequencies were presented. They
were 500 cps, 2000 cps, and 8000 cps. One of the purposes
of this study was to determine if certain auditory frequen-
cies allow for a more accurate judgment of distance than
other auditory frequencies.

The second condition investigated in this study
concerned the type of presentation of the auditory signal.
The two types of presentation were continuous tones and
intermittent tones. Another purpose of this thesis was to
determine which type of presentation allows for more accuracy
in the judgment of distance from a sound.

The third condition of this study dealt with the
manner in which the blind individual's initial distance
from a sound source affected his perception of a distance
of ten feet. The subjects were randomly placed at three
different starting distances from the sound source. Those

distances were 26 feet, 38 feet, and 50 feet.

CHAPTER IV
RESULTS AND DISCUSSION

maria

A 3 x 3 x 2 factorial analysis of variance was
employed to determine the significance of differences
between mean scores.1

Six basic questions were posed at the outset of this
study, namely:

1. Do certain auditory frequencies allow for a more
accurate judgment of distance than other auditory
frequencies?

2. How does initial distance from a sound source affect
the blind individual's perception of another pre-
determined distance?

3. Which type of presentation allows for a more accurate
judgment of distance: a continuous or intermittent
tone?

4. Is there a dependence of presentation (continuous vs.
intermittent) on distance from the sound source in the
auditory perception of a distance of ten feet?

5. Is there a dependence of auditory frequency on initial

distance from a sound source in the auditory perception

 

1Allen L. Edwards, Experimental Design_in Psycho-
lo ical Research, (rev. ed.; New York: Rinehart Co., Inc.,
1950), p. 201-07.

19

20

of a distance of ten feet?

6. Is there a dependence of auditory frequency on presen-
tation (continuous vs. intermittent) in the auditory
perception of a distance of ten feet?

The results of the analysis of variance are

indicated in Table 1.

TABLE 1
ANALYSIS OF VARIANCE

 

 

 

Source of Sum of d. f. Mean F
variation Squares , Square

Frequency (F) 1927.72 2 963.86 ....
Distance (D) 264.05 2 132.03 ....
Presentation (P) 7921.79 1 7921.46 3.24*
F x D 21233.79 4 5308.45 2.33*
F x P 169.73 2 84.87 ....
D X P ~. 5401.06 2 2700.53 1.66*
F x D x P 4907.75 4 1226.94 ....
Within

Treatments.~ 41825.56 18 2323.64 ....
TOTAL 83651.12 35

 

*The resulting F was not statistically significant
at the .05 level of confidence

Inspection of Table 1 reveals that no significant
F ratios were obtained at the .05 level of confidence. The

triple interaction variance (F x D x P) was combined with

21

the Within Treatments variance in an effort to further
evaluate for significant results. No significant F scores,
however, resulted from this procedure at the .05 level of

confidence.

Discussion

There was no statistically significant difference
in the three frequencies relative to judgments of distance.
No one frequency yielded more accurate judgments over
another. Auditory frequency was not demonstrated to be a
significant variable as it pertained to a judgment of dis-
tance from a sound.

There was no statistically significant difference
in the three starting distances relative to the judgment
of a sound source.

There was no statistically significant difference
in manner of presentation of the stimulus relative to a
judgment of distance. Neither the continuous nor the inter-
mittent tone was demonstrated as allowing a more accurate
judgment.

After assessing the statistical significance of the
three parameters of this study, the interaction among these
variables was computed. The interaction of presentation by
distance was not statistically significant as it pertains
to accuracy in the judgment of distance. The interaction
of frequency by distance was not statistically significant

relative to accuracy in the judgment of distance. The

22

interaction of frequency by presentation was not a statis-
tically significant variable influencing the accuracy in
judgment of distance.

The physical dimension of the auditory stimulus in
the present investigation was held constant for each subject.
Due to the acoustical properties of the room, however, the
subjects may have perceived variations in intensity.for the
various distances. These variations in intensity were
measured by a Mine Safety Appliance sound pressure level
meter. The ambient noise in the test room at ten feet from
the sound source was 46 db. The auditory frequencies pre-
sented were analyzed by a narrow band filter with a range
of 200 cps above and below each frequency. The measurements
are indicated in Table 2.

In this regard Békésy notes that "an increase in
loudness produces a clear reduction in the distance of the
diffuse image. Thus it seems that loudness has an effect
upon the perceived distance only in the absence of the other
more determinant physical cues."1

There are several factors which might account for
the negative results of this study. One factor is the size
of the sample utilized. A larger sample might have yielded
significant results, especially with regard to the frequency
by distance interaction. The frequency by distance F ratio
obtained was 2.33; an F ratio of significance at the .05

 

/
1Bekésy, op, cit., p. 304.

23

level of confidence is 2.93. As previously suggested, a

larger sample might have indicated significant results.

TABLE 2
SOUND PRESSURE LEVELS IN TEST ROOM

 

 

 

Frequency Distance from Sound Pressure
Analyzed Sound Source Level
500 cps. 10 feet 55 db.
500 cps. 26 feet 56 db.
500 cps. 38 feet 51 db.
500 cps. 50 feet 52 db.
2000 cps. 10 feet 41 db.
2000 cps. 26 feet 38 db.
2000 cps. 38 feet 36 db.
2000 cps. 50 feet 39 db.
8000 cps. 10 feet 56 db.
8000 cps. 26 feet 40 db.
8000 cps. 38 feet 33 db.
8000 cps. 50 feet 32 db.

 

Another factor which might account for the negative
results of this study concerns the acoustic characteristics
of the test room. Although the reverberation time for the
room was relatively low (1.24 seconds), it is conceivable

that the time lag and accompanying distortions might have

influenced the subjects perception of distance from a sound

24

source. Conducting this same experiment in an anechoic
chamber might reveal different findings.

It is particularly interesting to note that frequency
did not play a significant role in the perception of dis-
tance from a sound source by the blind. This finding stands
in contradiction to some of the findings in the review of
the literature. Griffin, for example, stated that the
higher pure tones (around 10,000 cps) provide for more
accurate perception of obstacles than the lower frequencies
(125-8000 cps). Again, the acoustical characteristics of
the room might account for this apparent discrepancy.

In summary, the findings of this study do not support
the hypothesis that auditory frequency, method of presen-
tation, and distance as defined in this thesis are signif-
icant variables relative to the blind individual's judgment
of distance from a sound source. Both the size of the
sample and the acoustical characteristics of the test room

are factors which might account for the negative results.

CHAPTER V

SUMMARY AND CONCLUSIONS

Summary
This study is concerned with the auditory skills of

blind individuals. It investigates one aspect of the ways
blind individuals utilize sound in mobility and orientation.
The purpose of this thesis was to analyze the effects of
auditory frequency and manner of presentation of signals

on judgment of distance by blind individuals. Six basic
questions were posed at the outset of the research. These
questions were initially posed in Chapter I and elaborated
on in Chapter IV.

A review of the literature revealed some studies
which related to this thesis but none which had a similar
experimental design. Earlier research by Cotzin and Dallen-
bach1 and more recent investigations by Griffin2 infer that
the higher auditory frequencies might allow for the greatest
accuracy in the judgment of distance from a sound source.

Several authors3:4 have indicated some of the

variables affecting the perception of the distance of a

 

1Cotzin and Dallenbach, op, cit., p. 512.
2Griffin, Listeningfin the Dark, 100. cit.
3Harvey Fletcher, op. cit., pp. 221-22.
4Békésy, op, cit., p. 208.

25

26

sound source. These variables include auditory frequency,
distance from the sound source, manner of presentation of
the auditory stimulus, intensity of the auditory stimulus,
and acoustical characteristics of the environment.

The experimental procedure utilized thirty-six
visually handicapped students at the Michigan School for
the Blind. Each of them had normal hearing and average
intelligence or above average intelligence. Nearly all of
the subjects were blind at birth.

Three primary variables were investigated in this
study. The first variable was auditory frequency. The
three frequencies utilized were 500 cps, 2000 cps, and
8000 cps. Another variable was the manner of presentation
of the sound stimulus. Both a continuous tone and an
intermittent tone were employed in the experimental pro-
cedure. The pure tone auditory signals in this study were
generated from an audiometer through a speaker into the
test room. The third variable was the distance from the
sound stimulus. The subjects were positioned at three dif-
ferent distances from the sound source; those distances
were 26 feet, 38 feet, and 50 feet.

The subjects were led into the test room and given
the instructions outlined in Chapter III. Next, they were
taken to a location exactly ten feet from the sound stimulus.
Each subject was randomly presented one stimulus. It was

one of the three frequencies mentioned above and was

27

presented as a continuous tone or an intermittent tone.
The table in Appendix C indicates the exact conditions for
each subject.

After the subjects had the opportunity to hear their
stimulus at a distance of ten feet from the sound source,
they were disoriented in the room and repositioned at
either 26 feet, 38 feet, or 50 feet from the sound stimulus.
Their instructions were to walk forward until they again
perceived the distance of ten feet from the sound source.
Their only clue was the auditory stimulus presented to them.
Each subject participated in just one condition.

The error judgment for each Subject was measured and
recorded. An analysis of variance was computed to determine
the significance of differences among mean scores. The
results of the statistical computation revealed nonsignif-
icant findings. None of the F scores were statistically
significant at the .05 level of confidence. This study
indicated that auditory frequency, distance from the sound
source, and manner of presentation of the auditory stimulus
were nonsignificant variables affecting the perception of
distance from a sound source by the blind. The interactions
between these variables were also nonsignificant at the
.05 level of confidence. It is conceivable, however, that
a larger sample and a change in the acoustical specifications
of the environment might find one or more of these variables

more significant than indicated in this study.

28

W
The following conclusions are noted on the basis of
the results obtained in this investigation:

1. It cannot be said that any of the auditory frequencies
investigated allows for a more accurate judgment of
distance from a sound source than the others.

2. It cannot be said that the initial distance from a
sound source affects blind individuals' perception of
another predetermined distance.

3. It cannot be said that either type of presentation
(continuous vs. intermittent) allows for a more accurate
judgment of distance than the other.

4. It cannot be said that there is a dependency of pre-
sentation (continuous vs. intermittent) on distance
from the sound source in the auditory perception of a
distance of ten feet.

5. It cannot be said that there is a dependency of auditory
frequency on initial distance from a sound source in
the auditory perception of a distance of ten feet.

6. It cannot be said that there is a dependency of auditory
frequency on presentation (continuous vs. intermittent)

in the auditory perception of a distance of ten feet.

Implications for Future Research
It would be interesting to repeat this experiment
With a larger number of subjects. Since the F for frequency

by distance interaction was almost statistically significant

29

at the .05 level of confidence, a larger sample might yield
significant results.

Additional research relative to the function of
auditory signals in the perception of distances is needed.
It might be found that some type of mechanical guidance
device emitting an auditory signal could be utilized by the
blind in negotiating the obstacles of their environment.
Also, such a device might be employed by the military in
detecting obstacles at distances which cannot now be located

by conventional means.

B IBLIOGRAPHY

31
Eagles

Davis, Hallowell, and Silverman, Richard. Hearing and Deaf-
ness. New York: Holt-Rinehart and Winston, Inc., 1960.

Edwards, Allen L. Experimental Design in Psychological
Research. rev. ed. New York: Rinehart and Co., Inc.,

19 0.

Fletcher, Harvey. Speech and Hearing in Communication.
Princeton, New Jersey: D. Van Nostrand Co., Inc.,

1958.

Griffin, Donald R. Listenin in the Dark. New Haven: Yale
University Press, 1958.

Hirsh, Ira J. The Measurement of Hearing. McGraw-Hill Co.,
Inc., 195 .

Lowenfeld, Berthold. Our Blind Children. Springfield,
Illinois: Charles C. Thomas Pub., 1956.

Newby, Hayes A. Audiology. New York: Appleton-Century-
Crofts, Inc., 1958.

von Bakesy, Georg. Experiments in Hearing. New York: McGraw-
Hill Co., Inc., 19 O.

Zahl, Paul. Blindness. Princeton, New Jersey: Princeton
University Press, 1950.

Articles

Cotzin, M., and Dallenbach, K. M. "Facial Vision: The Role
of Pitch and Loudness in the Perception of Obstacles
by the Blind," American Journal of Ps cholo , LXIII
(1950), 512. ,

Fedderson, W. E. et al. "Localization of High Frequency
Tones," Journal of the Acoustical Societ of America,
XXXIX (September, 1957), 98 -91.

Fletcher, John L. "Localization of Sounds in Depth," U. S, A,
Medical Research Labopatory Report, MCMLVII, No. 302
11 (1957). 14:

32

Griffin, Donald R. "Acoustical Orientation in the Oil Bird,
Steatornis," National Academ of Sciences, XXIX,

McCarty, B., and Worchel, P. "Rate of Motion and Object
Perception in the Blind," New Outlook for the Blind,
XLVII (November, 1954), 316

O'Neill, John, Oyer, Herbert, and Baker, Donald. "Auditory
Skills of Blinded Individuals Training With Pilot
Dogs," Journal of S eech and Hearing Research, I,
No. 3 (September, 1953). 262-67. '

Supa, M., Cotzin, M., and Dallenbach, L. M. "Facial Vision:
The Perception of Obstacles by the Blind " American

Journal of Psychology, LVII (April, 1944 .183.

 

Weiss, Carl. "Reality Aspects of Blindness As They Affect
Case Work," The Famil , (February, 1954) 12.

Zwislocki, J., Hellman, R. P., and Verillo, R. T. "Threshold
of Audibility for Short Pulses," Journal of the

Acoustical Society of America, XXIV, No. 10 (1962),
1 -52 o

Unpublished Materia;

American Association of Instructors of the Blind, "Orien-
tation and Mobility Terms," St. Louis, Missouri,
March, 1962. (Mimeographed.)

Appendix A

34

Appendix A

ACOUSTICAL SPECIFICATIONS OF ROOM
WHERE STUDY WAS CONDUCTED*

 

r fi

 

Surface Material Area Coef. Absorb.
Ceiling Tectum 2" 5800 .65 3700
Floor Asphalt Tile 5700 .03 171
Wainscott Plastic Paint 2250 .06 135
Walls Painted Block 5260 .06 314
‘Walls Tectum 2" 2037 .65 1324
Air 143,000 éu. ft. 143
TOTAL 5787

 

Room dimensions: 62 feet by 92 feet
5,700 square feet
143,000 cubic feet

 

Reverberation time: Key:
Formula: T = ,05V T = reverberation
a time
T : .05 (143.000) V = room volume
5857
a = total
T = 1.24 absorbtion

*Source: Building Division, State of Michigan

Appendix B

36

Appendix B
INTENSITY OF THE STIMULI

 

 

 

Cycles Minimum Audible Intensity Level
Per Sound Field In Of Presented
Second Reference to Atten- Stimuli in Refer-
uator Setting* ence to Atten-
uator Setting

500 35 db. 85 db.

2000 30 db. 80 db.

8000 30 db. 80 db.

 

*The intensity of the stimuli utilized in this

emperical study was presented at 50 decibels above the

minimum audible field.

The minimum audible field was

ascertained by determining the threshold for each of the
three frequencies tested at a distance of three feet from

the source.

This procedure was conducted sound field in

the actual test room on a pair of normal ears.

Appendix C

PRESENTATION OF STIMULI

38

Appendix C

 

 

 

Subject Starting Frequency Tone
Number Distance Tested Presentation

1 26 feet 500 cps. Intermittent
2 38 feet 500 cps. I

3 50 feet 500 cps. I
4 26 feet 2000 cps. I

5 38 feet 2000 cps. I

6 50 feet 2000 cps. I
7 26 feet 8000 cps. I

8 38 feet 8000 cps. I
9 50 feet 8000 cps. I
10 26 feet 500 cps. Continuous
11 - 38 feet 500 cps. C
12 50 feet 500 cps. C
13 26 feet 2000 cps. C
14 38 feet 2000 cps. C
15 50 feet 2000 cps. C
16 26 feet 8000 cps. C
17 38 feet 8000 cps. C
18 50 feet 8000 cps. C
19 26 feet 500 cps. I
20 38 feet 500 cps. I
21 50.feet 500 cps. I
22 26 feet 2000 CPS. I
23 38 feet 2000 cps. I
24 50 feet 2000 cps. I
25 26 feet 8000 cps. I
26 38 feet 8000 cps. I
27 50 feet 8000 cps. I
28 26 feet 500 cps. C
29 38 feet 500 cps. C
30 50 feet 500 cps. C
31 26 feet 2000 cps. C
32 38 feet 2000 cps. C
33 50 feet 2000 cps. C
34 26 feet 8000 cps. C
35 38 feet 8000 cps. C
36 50 feet 8000 cps. C

 

Appendix D

40

Appendix D
ERROR JUDGMENT FOR EACH SUBJECT IN INCHES

 

 

Subject Error Judgment

 

1 54 Inches

2 7 Inches

3 54 Inches

4 10 Inches

5 111 Inches

6 216 Inches

7 28 Inches

8 51 Inches

9 85 Inches
10 72 Inches *
11 6 Inches
12 39 Inches
13 7 Inches *
14 34 Inches
15 55 Inches
16 9 Inches
17 21 Inches
18 22 Inches
19 192 Inches
20 10 Inches
21 7 Inches
22 46 Inches
23 5 Inches *
24 31 Inches
25 120 Inches
26 72 Inches
27 11 Inches
28 8 Inches *
29 31 Inches
30 2 Inches
31 3 Inches *
32 120 Inches *
33 47 Inches *
34 8 Inches
35 58 Inches
36 35 Inches *

 

*Nearly all of the subjects tended to overestimate
the judgment of ten feet. The asterisk indicates those
subjects who underestimated the judgment of ten feet.

MEAN SCORES IN INCHES

41

0F ERROR JUDGMENTS

 

 

 

variable Conditions of Mean Score
Variable
Frequency 500 cps. 40.27 Inches
2000 cps. 57.08 Inches
8000 cps. 43.33 Inches
Presentation Continuous 32.06 Inches
Intermittent 61.72 Inches
Distance 26 feet 46.42 Inches
38 feet 43.83 Inches
50 feet 50.42 Inches
F x P 500 cps. - Continuous 26.33 Inches
2000 cps. - Continuous 44.33 Inches
8000 cps. - Continuous 25.50 Inches
500 cps. - Intermittent 54.17 Inches
2000 cps. - Intermittent 69.83 Inches
8000 cps. - Intermittent 61.17 Inches
F x D 500 cps. - 26 feet 81.50 Inches
500 cps. - 38 feet 13.50 Inches
500 cps. - 50 feet 25.75 Inches
2000 cps. - 26 feet 16.50 Inches
2000 cps. - 38 feet 67.50 Inches
2000 cps. - 50 feet 87.25 Inches
8000 cps. - 26 feet 41.25 Inches
8000 cps. - 38 feet 50450 Inches
8000 cps. - 50 feet 38.25 Inches
F x D Continuous - 26 feet 17.83 Inches
Continuous - 38 feet 45.00 Inches
Continuous - 50 feet 33.33 Inches
Intermittent - 26 feet 75.00 Inches
Intermittent - 38 feet 42.67 Inches

Intermittent - 50 feet

67.50

Inches

 

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