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THESIS

LIBRARY

Michigan State
University

 

ABSTRACT

SENSITIVITY OF THE SKIN TO
PURE TONE FREQUENCIES

by Milen Gray

Two groups, comprising thirty-two adolescents and
thirty-two adults, were tested to determine to what degree
the sensitivity of the skin, in relation to the ability to
perceive changes in vibratory sensitivity, is affected by
increasing age. This sensitivity was tested by placing a
transducer, against the palm of the subject's right hand.
A pure tone was introduced into the transducer from a low
frequency audio oscillator at an input intensity of 100
decibels (re 0.002dyne/cm2). The intensity level was held
constant during the course of the study. Frequency was
varied logarithmically. The test frequencies for this
study ranged from 10 to 2000 cycles per second.

Upon completion of the study the test frequencies
were divided into 50 cycle band widths. The total number
of reSponses obtained from the adult and adolescent groups
were tabulated for each 50 cycle band width. The responses
obtained for each band width were then compared for the

adult and adolescent groups only up to a limit of 500Cps.

MILEN GRAY

The results of this comparison indicated no statis-
tically significant differences between these groups except
in the l-SOcps frequency range. A comparison of tactile
sensitivity within each group to sound stimuli of selected
frequencies was then made. Within the adult group a
statistically significant difference was obtained for two
of the three sets of frequencies tested. Within the
adolescent group a statistically significant difference
was obtained for each of the three sets of selected
frequencies tested.

In relation to age as a factor in the ability of the
skin to respond to changes in pure tone signals there
seems to be little difference between the adolescents and
adults used in this study. The only significant difference
would be in favor of the adolescent group in responding to
low frequency pure tone signals in the l-50cps range. The
greatest differences in cutaneous sensitivity seem to occur
within each group. In this respect the adolescent group
would seem to have a greater range in cutaneous responses
to pure tone signals than would the adults. This, however,

is still confined to the low frequency ranges.

SENSITIVITY OF THE SKIN TO

PURE TONE FREQUENCIES

By

Milen Gray

A THESIS

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

MASTER OF ARTS

Department of Speech

196A

 

G, I; "A '3 "3 'w“

ACKNOWLEDGEMENTS

The assistance of the Superintendent and Director
of Special Education of the Berrien County Intermediate
School District is greatly appreciated for their co-
operation in making the time and office facilities avail-
able for the writing of this thesis.

The assistance of the Watervliet High School,
Watervliet, Michigan, Fraternal Order of Elks, Lodge 544,
Benton Harbor, Michigan and the Benton Harbor chapter
of the Kappa Theta Chi sorority is gratefully acknowledged
for their help in providing the subjects used in this

study.

ii

TABLE OF CONTENTS

Page
ACKNOWLEDGEMENTS . . . . . . . . . . . . ii
LIST OF TABLES . . . . . . . . . . . . iv
LIST OF FIGURES . . . . . . . . . . . . v
LIST OF APPENDICES . . . . . . . . . . . vi
Chapter

I. NATURE AND IMPORTANCE OF THE PROBLEM . . 1
II. REVIEW OF THE LITERATURE. . . . . . . A
III. SUBJECTS, EQUIPMENT, AND TESTING PROCEDURE. 12
IV. RESULTS AND DISCUSSION . . . . . . . 18

V. SUMMARY, CONCLUSIONS. AND SUGGESTIONS FOR
FURTHER RESEARCH . . . . . . . . . 26
APPENDICES . . . . . . . . . . . . . . 30
BIBLIOGRAPHY . . . . . . . . . . . . . 38

iii

LIST OF

TABLES

Number and Percentage of Subjects
Responding to Test Frequencies

Comparison of Subjects for Test Frequencies

l-500cps in 50 Cycle Band Wid

\A

Tactile Sensitivity of Adults to Sound

Stimuli of Selected

Tactile Sensitivity of
Stimuli of Selected

-

L

'hs

Test Frequencies

Adolescen
Test Freq

iv

‘.
KI'
‘ 1
U.

s t

611’1 C

o
i

63.

Sound
s

O

21

22

23

LIST OF FIGURES
Figure Page

1. Percentage of adults and adolescents
responding to test frequencies l~2000
cycles per second in 50 cycle band
widths .

LIST OF APPENDICES

Appendix

I. Total Number of Responses, Within 50
Cycle Band Widths, for Test Frequencies
l—200cps for Adult Population .

II. Total Number of Responses, Within 50
Cycle Band Widths, for Test Frequencies
l-20000ps for Adolescent Group.

III. Test Form Based on Logarythmic Pure Tone
Frequency Scale. . . . . . .

vi

Page

31

33

35

CHAPTER I

THE NATURE AND IMPORTANCE OF THE PROBLEM

This study is concerned with the measurement of
perceived changes in vibratory stimuli as a function
of age.

The purpose of this study is to analyse the results

obtained from adolescents and adults in response to
changes in pure tone frequencies introduced through the
skin.

It is hoped that this study will provide answers to

the following questions:

1. Is there a significant difference between adoles-
cents and adults in the ability to notice grad-
uated changes in pure tone frequencies introduced
through the skin?

2. Are there any significant differences in tactile
sensitivity in relation to selected pure tone
frequencies within the adult population?

3. Are there any significant differences in tactile
sensitivity in relation to selected pure tone

frequencies within the adolescent population?

Hypotheses

 

To answer the above questions the following null

hypotheses have been proposed.

1. There is no significant difference in the
responses of adults and adolescents to changes
in pure tone frequencies introduced through
the skin.

2. There is no significant difference in tactile
sensitivity to selected pure tone frequencies
within the adult population.

3. There is no significant difference in tactile
sensitivity to selected pure tone frequencies

within the adolescent population.

Importance of the Study
It is thought that a measure of cutaneous sensitivity
to sound stimuli might be valuable in planning for future
developments that would utilize this avenue in the rehabili-

tation of the hard of hearing person.

Definition of Terms
For the purpose of this study, the terms used are
defined in the following manner:

Adolescent Population--Individuals ranging in age

 

from thirteen to twenty-one years of age.

Adult Population--Those individuals over twenty-

 

one years of age.

Cutaneous Area--Relating to the fatty portion of the

 

inner palm of the right hand.
Vibratory Sensitivity-—Sensitivity of the skin to
stimulation by a vibrating medium as introduced through

electrical current.

CHAPTER II

REVIEW OF THE LITERATURE

The Effects of Age on Vibratory Sensitivity

 

In a review of the literature pertaining to the
relationships between vibratory sensitivity and age, a
decrease of vibratory sensitivity in the later periods
of life has been noted. There tends to be a loss of
sensitivity in the ability of the skin to perceive
vibration.l

According to Pearson other authors have noted the
decrease of this sensory modality. This sensitivity
seems to be greater in childhood and adolescence and then
seems to diminish with age, particularly after the fifth
decade. Pearson also found that the ability to perceive
vibratory stimuli from the lower extremities becomes im-
paired in most persons after the fifth decade. Pearson
noted that Egger found that although vibratory sensitivity
may decrease with advancing age, a number of persons tested
by him aged 60, 70, and 80 and one over a hundred retained

their acutness of perception.2

 

1James E. Birren, "Vibratory Sensitivity in the Aged,"
Journal of Gerontology, II (1947), 267-268.

 

2G. H. J. Pearson, "Effect of Age on Vibratory Sensi-
Eility,” Archives of Neurology and Psychiatry, xx (1928),
82-496.

 

4

The Range of Cutaneous Sensitivity

Geldard noted in reviewing the range of frequencies
yielding sensations of vibration that whereas it is found
that little agreement exists as to what the upper and
lower limits are, various curves uniting frequency and
threshold amplitude are somewhat universal. Geldard
makes note of the maximum sensitivity as being in the
region of 250 cycles per second. However, the upper limit
is not known because of the technical difficulties of

moving the skin at high frequencies.3

Cutaneous Sensitivity in Relation
to Body Areas

 

Mason noted that:
A distinction is frequently made between sensations

of touch, relating to light contact, and of pressure,
relating to increased application of force

in cutaneous sensitivity studies.LL
Gilmer found that: (l) The regions of the skin most

sensitive to mechanical vibration were those spots which

were also highly sensitive to pressure, (2) There was a

marked difference between the dorsal and ventral sides of

the arm with respect to vibratory sensitivity stimulation.

 

3F. A. Geldard, "The Perception of Mechanical Vibra-
tion," Journal of General Psychology, XXII (1940), 281-289.

4R. E. Mason, Internal Perception and Bodily Function-
in (New York: International Universities Press, Inc.,
1951 , p. 344.

In general, the data support the hypothesis that vibratory
sensations form a perceptual pattern of feeling of which
pressure is but another temporal expression.5
Geldal’dagreeswith Gilmer’s pressure hypothesis
and goes on to state in somewhat different phraseology that
"vibration involves a mode of operation of the pressure
sense." Geldard in reviewing the literature pertaining to
the effect of changing the pressure component of the stimu-
lation noted that Cohen and Lindley (1938), found vibratory
thresholds (for a single frequency, 60cps) to be lowered
by increased pressure applied to the contactor. This
effect they attributed to "mechanical factors of increased
compression of tissue which under such circumstances may
become a better medium for the conduction of vibration."
Godfrey (1934), delivering low frequency vibrations (25-
lOOcps), found resulting sensations to be localized further
and further from the fingers with increasing pressure.
Knudsen found that the amplitude of vibration, for a
given frequency, seemed to be the important factor in de-

termining the intensity of vibration, and the amplitude of

 

5B. V. H. Gilmer, ”The Measurement of the Sensitivity
of the Skin to Mechanical Vibration,” Journal of General
Psychology, XIII (1935), 42-61.

6F. A. Geldard, ”The Perception of Mechanical Vibra-
tion: I. The History of the Controversy," Journal of
General Psychology, XXII (1940» 243-269.

 

vibration was used in measuring sensitivity. The
frequency of a vibrating body must change as much as 15
to 30 percent before a difference is noticeable by the
sense of touch. Touch is not well adapted to recognizing
small changes of frequency.7

Babkin, el~jal,, discovered a close relationship be-
tween the magnitude of stimulated surface and the measured
threshold of perceived vibration: increase of stimulated
area leads to decrease of threshold.8

Gilmer in a study dealing with the sensitivity to
mechanical vibration of different regions of the hand and
forearm found that the most sensitive areas tested were
the fatty portions of the palmer side of the hand and
finger tips. He also noted that larger contacting media
gave smaller values when lower frequencies were used; at
higher frequencies size was not a variable.9

Shewchuk and Zubek studied the discriminatory ability

of various skin areas as measured by a means of intermit-

tent stimulation. The technique used was an interrupted

 

7V. 0. Knudsen, "Hearing With the Sense of Touch,"
Journal of General Psychology, I (1928L 320-352.

 

8V. P. Babkin, 0. M. Rozen, L. N. Turmarkina, and
R. I. Cherniak, ”The Study of Vibrational Sensitivity and
the Factors Influencing It," Biofizika, VI (1961), 61—67.

 

9B. v. H. Gilmer, "The Measurement of the Sensitivity
of the Skin to Mechanical Vibration," Journal of General
Psychology, XIII (1935), 42-61.

 

 

air stream that stimulated the tongue, lip, cheek, fore-
head, neck, tip of the index finger, thumb, back of the
hand, forearm and upper arm. For each of these locations
a critical frequency of percussion (cfp) was determined.
The relationship between (cfp) and pressure was the same
for all 10 skin areas tested. The (cfp) for the lip,
tongue, and thumb was higher than that of the arms, neck,
and cheek.10
Békésy commented that it is known that the skin of
the arm is less sensitive than the skin on the thumb. He
further commented that this difference is a consequence of
the fact that the area of the sensory cortex correSponding
to a unit of surface on the thumb is much larger than that

correSponding to a unit of surface on the arm.11

Adaptation and Fatigue of the Skin
to Cutaneous Stimulation

 

 

Wedell and Cummings studied fatigue of the vibratory
sense. They discOvered adaptation to be a function of both
amplitude and frequency, being greater for the higher
values of each. They also found that sensitivity to Vibra—

tory stimulation applied to the palm of the hand is reduced

 

10L. A. Shewchuk and John P. Zubek, ”Discriminatory
Ability of Various Skin Areas as Measured by a Technique of
Intermittent Stimulation,” Canadian Journal of Psychology,

XIV (1960), 244-2u8.

llGeorg von Békésy, Egperiments in Hearing (New York:
McGraw—Hill Book Co., 1960), pp. 564—565.

 

fi' 5 to 15 decibels after three minutes of continuous stimu-

f lation. The loss of sensitivity is greater, the higher

the frequency, and the greater the intensity of the

V fatiguing tone. The effect proved to be somewhat non-

 

specific in that, after three minutes of continuous

stimulation, the loss was the same for a test frequency

higher than or equal in frequency to the fatiguing one.

Less decline had apparently occured if the test frequency

was lower than the original.12

 

 

Katz found that the sense of touch tires very

‘5“ .6

HT

readily but that the Vibratory sense shows very little

1.,

the effects of fatigue.13

 

Relationship Between Cutaneous Sensi-
tivity and Other Modalities

 

Békésy noted that:

When continuous vibratory stimuli are presented
on the skin the subject can differentiate several
attributes: (l) the frequency of the vibration,
which is analogous to pitch in hearing, (2) the
subjective magnitude of the sensation, which has
many features- in common with loudness in hearing
and (3) the sensation of the lateral spread along

the surface of the skin, which iprresponds to the
volume of the sound in hearing.

 

__m"-‘-|.‘I?_ JD. .-
. 1'- '

____-

d“. C. T

 

 

 

 

120. H. Wedell and s. B. Cummings, Jr., "Fatigue of

the Vibratory Sense,‘I Journal of Experimental Psychology,
XXII (1938), 429-438.

13K. Katz, ”The Vibratory Sense and Other Lectures,”
The Maine Bulletin, XXXII (1930), p. 10.

lLLGeorg von Békésy, "Funneling in the Nervous System,”

Journal of the Accoustical Society of America, XXX (1958),
399-412.

10

These three attributes Békésy referred to as vibratory
pitch, or pitch; vibratory magnitude, or loudness; and
lateral spread.

Hawkes concluded that auditory or cutaneous signals
will generally be usable in the situation where the
observer's task is to detect the presence or absence of
a signal.15

Yacorzynski in attempting to determine the minimal
number of vibratory thresholds, as a function of amplitude
of stimulation at different frequencies noted in conclusion
that:

It is necessary to study the vibratory threshold of
an individual case over a number of days in order to

get a good approximationéof his actual threshold under
the conditions studied.

Summary of the Literature

 

It has been noted, in reference to the relationship
between vibratory sensitivity and age, that this sensitivity
seems to be greater in childhood and adolescence and then
tends to decrease with advancing age but not always consis—
tently. In reference to the range of frequencies yielding
sensations of vibration there seems to be little agreement

as to the upper or lower limits, although one author notes

 

15G. R. Hawkes and M. Loeb, "Vigilance for Cutaneous
and Auditory Signals," Journal of Auditory Research, I

(1961). 272-284.

1

6G. K. Yacorzynski and M. Brown, "Studies of the
Sensation of Vibration,” Journal of Experimental Psychology,
XXVIII (1941), 509—516.

 

11

the maximum range of sensitivity as being in the region of
250cps. In cutaneous sensitivity studies a distinction is
frequently made between sensations of touch and of pressure.
It is generally felt that the use of pressure, relating to
the increased compression of tissue, provides a better
medium for the conduction of vibration than does that of
touch, relating to light contact. There seems to be

little specific agreement regarding those areas of the

body which may be regarded as more sensitive to vibratory
stimulation than others. It has been noted that the
sensitivity of the skin to vibratory stimulation tends to
diminish after a period of continuous stimulation. This
loss of sensitivity appears to be greater the higher the
frequency and the greater the intensity of the fatiguing
tone. It was noted in some instances with the presentation
of vibratory stimuli onthe skin the subject can differen—
tiate some attributes which are similar to pitch, loudness
and volume in hearing. It was also felt that cutaneous
signals can generally be used in situations where the
observer's task is to determine the presence or absence

of a signal.

CHAPTER III

SUBJECTS, EQUIPMENT, AND TESTING PROCEDURES

Subjects
The first group of subjects participating in this

study consisted of thirty-two high school seniors from
the Watervliet High School, Watervliet Michigan. The
second group of subjects participating in this study
consisted of thirty-eight adults drawn from the member-
ship of Lodge 544, Fraternal Order of Elks, Benton
Harbor, Michigan and the Benton Harbor chapter of the
Kappa Theta Chi sorority. The sole criteria for partici-
pation in this study was that of age.

The adult group consisted of thirty-six Caucasians
and two Negroes. All members of the adolescent group were
Caucasian.

0f the thirty-eight adults tested six were eliminated
from this study because of failure to respond to any
frequency tested. Their failure to respond to this study
is open to question either because of lack of skin
sensitivity, misunderstanding of directions, or some other

unknown cause. The members of this group consisted of

12

13

one male thirty-four years of age, one Negro male sixty-
five years of age, three females thirty-five, forty-three,
and forty-seven years of age, and one Negro female forty-
seven years of age. The remaining thirty-two adult sub-
jects used in this study consisted of twenty-one males and
eleven females ranging in age frOI 24 to 78.4 years with

a mean age of 43 years, a median age of 41.6 years and a
standard deviation of 4.2 years.

The thirty-two adolescents used in this study con-
sisted Cf nine males and twenty-three females ranging
in age from 16.9 years to 18.7 years with a mean age of
16.2 years, a median age of 17.4 years and a standard
deviation of .04 years.

The original seventy subjects were tested during the
week of September 30 to October 4, 1963. The adolescent
group was tested in the morning and afternoon of October 1,
1963 at the Watervliet High School, in an unused room
provided for that purpose. The adult females were tested
during the evening of October lst at the private residence
of one of the members of the Kappa Theta Chi sorority. The
male adult members of the Fraternal Order of Elks were
tested at the lodge hall on the afternoon of and evening

of October 3rd and during the afternoon of October 4th.

14

Equipment

 

The equipment utilized for this study consisted of

the following:

1.

2.

One Acoustically Treated Plywood Box.

Four - Channel Master 2-1/4” Speakers affixed
with a tight membrane over the cone front,
mounted on a metal frame in such a manner as

to permit variation of pressure on the skin area.
A Low Frequency Audio Oscillator, Model No. 2020,
Hewlett-Packard, with a constant drive 115 volt
synchronous motor attached by a flat drive belt
to the frequency dial.

One Tape Recorder - Wollensak, Model No. T1500,
produced by the Minnesota Mining and Manufactoring
Company.

Tape recording of broad spectrum white noise.

One set of earphones - Telephonics TDH-39.

One desk bell.

Procedure

 

Orientation tO‘the Test Situation

 

Each subject was asked to participate in a scientific

experiment designed to test the sensitivity of the skin to

various pure tone frequencies. He was informed that he was

not being asked to make evaluations that would involve any

judgements of right or wrong on his part. The use of

the earphones and the introduction of broad spectrum white
noise to minimize auditory cues was also explained before-
hand. The use of the desk bell to indicate individual
responses as they were felt was explained. Each subject
was requested to ring the bell when he first felt the
presence of any type of sensation on the skin and to
continue to indicate any subsequent changes or differences
noted until a point was reached where no further changes

could be felt by the subject under test.

Procedure During Testing Situation

Each subject participating in the study was seated
at a table upon which rested an acoustically treated ply-
wood box. Contained within this box were four transducers
affixed with a tight membrane over the cone front. These
transducers were mounted on a metal frame in such a manner
so as to permit variation of pressure on the skin area.
This framework was placed in line with an insulated opening
in the side of the plywood box through which the subject's
right hand was introduced. The subject was requested to
place his hand so that the palmer area was facing the first
transducer. At this point the transducer was placed firmly
against the fatty portion of the palmer area by the tester

and the box closed. The subject was then given the

16

necessary instructions regarding the procedure to be
followed during the course of this study:

When the experiment begins you will at some point
begin to experience a type of vibration coming from
the Speaker cone resting against the palm of your
hand. As soon as you become aware of any type of
sensation against your palm I want you to ring this
desk bell and to continue ringing this bell each
time you feel any type of a change in the vibration ,
against your palm. We will continue as long as you 1
are able to experience any type of change in this
vibration or until the vibration seems to disappear.
Please remember that there are no right or wrong
answers involved in this experiment. I am only
interested in your reactions to the vibrations felt
against the palm of your hand. Do you have any
questions at this point?

 

After the initial instructions had been completed
the earphones were placed on the subject's head and broad
Spectrum white noise was introduced at a volume level
pre-determined by the tester. The subject was seated so
that a minimum of visual cues would be received through
observation of the tester or movements of the frequency
dial of the low frequency audio oscillator.

At this point a pure tone of loops was introduced
to the transducer from the audio oscillator at an input
intensity level of 100 decibels (re 0.002dyne/cm2). This
intensity level was held constant during the entire course
of this study. Frequency was varied logarithmically.

The rate of increase in frequency was controlled by a
115 volt constant drive synchronous motor attached to the

frequency dial of the low frequency audio oscillator by a

17

flat drive belt. Speed was thus held constant during

the course of the study. With each response of the subject
under test, indicated by the ringing of the desk bell, the
corresponding frequency response was read from the

frequency dial and entered on a form (see appendix 3, p. 30)
corresponding to the cycle units inscribed upon th
frequency dial.

The original band width to be tested was 40-900 cycles
per second. During the course of each test the initial
frequency level was lowered to loops and allowed to reach
a maximum of 2,000cps as long as the subject continued to
respond to the perceived vibration emanating from the
transducer. This was done to cover differences in level
of response for subjects in the test situation. The
elapsed time involved during the experiment was three
minutes with an additional four to five minutes for instruc-

tions and questions by the subject.

 

CHAPTER IV
RESULTS AND DISCUSSION

Upon completion of this study the test frequencies
1-2000 cycles per second were divided into 50 cycle band
widths ranging from 1-5OCps to 105l—2000cps. The total
number of responses obtained from the adult and adoles-
cent groups were then tabulated and the number of
responses entered for each 50 cycle band width (see
Appendix I, pp. 31-32 and Appendix II pp. 33-34).

The total number and percentage of adults and
adolescents responding to each 50 cycle band width are
presented in Table 1.

The number of adults responding within each 50
cycle band width shows a marked decrease at the lOl-l50cps
level. A similar decrease is noted for the adolescent group
at the 151-200cps levels. Although some irregular gain
is made for both groups beyond these frequency level up
to 651-700cps neither group approaches the 50 percent
level of numbers responding. The number of subjects re-
sponding to test frequencies 701—750 cps and beyond then
diminishes consistently for both groups.

Figure 1 presents a graphic illustration of the
reduction in cutaneous sensitivity according to the

18

19

percentage of subjects responding within each 50 cycle
band width. For the purposes of presentation the percen—
tages listed in Table l have been rounded to whole
numbers.

TABLE 1 --Number and percentage of adults and adolescents
responding to test frequencies in band widths of 50 cycles.

 

 

 

No. of No. of
Adol. Adults
Frequency Responding % Adol. Responding % Adults
Range Total-32 Responding Total-32 Responding
1-50 27 86.4 15 48.
51—100 31 99.2 30 96.
101-150 22 70.4 16 50.
151-200 16 50. 9 28.8
201—250 8 25.6 14 44.8
251-300 12 38.4 10 32.
301-350 12 38.4 3 9.6
'351-400 6 19.2 7 22.4
401—450 8 25.6 4 12.8
451-500 10 32. 5 16.
501-550 7 22.2 10 32.
551-600 5 16. 10 32.
601-650 3 9.6 3 9.6
651-700 8 25.6 5 16.
701-750 1 3.2 2 6.4
751-800 2 6.4 l 3.2
80l~850 4 l2. 2 6.4
851-900 4 l2. 0 . .
901-950 0 . . -1 3.2
951-1000 5 l6. 0 .
1001-1050 1 3.2 0 . .
1051-2000 1 3.2 2 6.4

 

The percentage of responses for the adolescent
group, in reference to peak response levels below the 50
percent level, at 200cps and for band widths 500,700, and

lOOOCps presents an almost gradual decrease with frequency

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21

intervals of 300, 200, and 300cps for the band widths

noted above. In comparison, the percentage of adult
responses below the 50 percent level at l5OCps takes a
sharp drop after 240cps; and the peaks remain compressed
for band widths 350, 700, 850, and 95OCps with frequency
intervals of 150, 300, 150, and lOOcps for the band widths
noted above.

The responses obtained within each 50 cycle band
width were then compared for the adult and adolescent
groups up to 500cps. The 451-500 cycle band width was
used as a cut off point for analysis due to the lack of
multiple responses, for either group, beyond this point.
The means and tfscores obtained from this comparison
appear in Table 2.

TABLE 2.—-An analysis of responses comparing adolescents

and adults for test frequencies 1-500cps in 50 cycle band
widths.

 

 

Frequency Mean Score Mean Score Level of
Range Adult Adolescent df _t Confidence
1-50 0.7500 1.9062 62 4.22 Sig. at 1%
51-100 2.0625 2.5372 62 1.52 Non sig5%
101-150 1.1562 1.1875 62 0.08 " 5%
151-200 .3750 0.5000 62 .83 ” 5%
201-250 .4375 .3125 62 .89 ” 5%
251-300 .3125 .3750 62 .52 ” 5%
301-350 .0937 .3750 62 1.48 ” 5%
351—400 .2500 .1875 62 .54 ” 5%
401-450 .1250 .2812 62 1.41 ” 5%
451-500 .1562 0.3437 62 0.99 ” 5%

 

22

As indicated the only statistically significant difference
for these groups appear in the l~500ps band width beyond
the 1 percent level of confidence. This statistically
significant difference for the adolescent group at the
1—50 cps level may be due to a greater sensitivity to
cutaneous stimulation for this particular range of low
frequency pure tone signals than for the adult group.
The responses for the adult and adolescent groups
were then analysed separately for a selected set of
test frequencies to determine if any significant differ-
ence existed within each group in relation to tactile
sensitivity. The means and t-scores for the comparisons
within the adult group appear in Table 3.

TABLE 3.--A comparison of tactile sensitivity within the
adult group to sound stimuli of selected frequencies.

 

 

 

Frequency Mean Level of
Range Score df .2 Confidence
l-50cps 0.7500
5l-lOOcps 2.0625 62 4.77 Sig. at 1%
1-50 cps 0.7500
101—150cps 1.1562 62 1.11 Non Sig. 5%
51-100cps 2.0625
101-15OCps 1.1562 62 2.32 Sig. at 5%

 

The means and t—scores for the adolescent group
appear in Table 4.

23

TABLE 4.--A comparison of tactile sensitivity within the
adolescent group to sound stimuli of selected frequencies.

 

 

Frequency Mean Level of
Range Score df 3 Confidence
1-5OCps 1.9062
51-100cps 2.5312 62 2.03 Sig. at 5%
l-50cps 1.9062
101-150cps 1.1875 62 2.44 ” 5%
5l-lOOcps 2.5312
101-150cps 1.1875 62 4.55 " 1%

 

As indicated the t-scores for the adult group are
statistically Significant at the l and 5 percent level of
confidence for two of the three sets of selected test
frequencies. The t-scores for the adolescent group being
statistically significant for all three sets of selected
test frequencies either at the 5 OP 1 percent level of
confidence.

In both instances where a statistically significant
difference was obtained, to selected pure tone frequencies,
within the adult group the critical frequency range was
5l—lOOcps. For the adult group this would appear to be
the frequency range which provides the greatest degree of
variability in sensitivity to cutaneous stimulation within
this population.

For the adolescent group the pure tone frequencies

yielding statistically significant differences were the

24

1-50 and 51-100 cycle band widths. There appears to be a
greater range of response to cutaneous stimulation for low
frequency pure tone signals within the adolescent group
than for that within the adult group.

In reference to Table 2, there does not seem to be
any differences, in relation to a decrease in vibratory
sensitivity according to age among adolescents and adults
except for frequencies ranging from 1-50 cycles per second.
The findings in this area are contrary to those noted in
Chapter II, p. 4, where sensitivity was reported as being
greater in childhood and adolescence and then tending to
diminish with increasing age. In some instances (see
Table l and Figure l.) the adult group exceeded the
adolescent group in different frequency ranges although not
significantly so. It is possible that with the use of
larger numbers of subjects and more precise equipment that
a more significant difference might be found to exist.

During the course of this study, subjects from both
the adult and adolescent groups reported that once the
pure tone signals, introduced through the skin, reached a
certain peak they rapidly diminished until no sensation
could be perceived. It would appear that the point where
the last response for each subject was recorded (see
Appendix I, pp. 31—32 and II, pp. 33-34) may be the last

point where any degree of sensation could be perceived by the

25

subjects tested in this study. This would tend to indicate
a wide range of individual thresholds in responses to
higher frequency ranges.

Inquiries regarding the type of sensation perceived
by individual subjects was almost universally one of
pressure which gradually increased and then diminished. A
number of comments were also made by the subjects to the
effect that as the sensation of pressure increased the
signal became localized further and further from the
original point of contact.

The six adults who failed to respond to any frequency
range (see Chapter III, p. 10) presented a problem which
was not expected at the beginning of this study. Although
care was taken that all subjects understood the directions
before the actual experiment began (see Chapter III, p. 13),
it is possible that the subjects failed to understand the
directions adequately and as a result did not respond to
the test frequencies as desired. It is interesting to
note that of the six subjects failing to respond in this
study four were females in their middle thirties or late
fourties. Another point of interest is the fact that of
the only two Negro subjects used in this study both

failed to respond to any of the test frequencies.

CHAPTER V

SUMMARY, CONCLUSIONS, AND SUGGESTIONS
FOR FURTHER RESEARCH

Summary

Two groups, comprising thirty-two adolescents and
thirty-two adults, were tested to determine to what degree
the sensitivity of the skin, in relation to the ability
to perceive changes in vibratory sensitivity, is affected
by increasing age. This sensitivity was tested by placing
a transducer, contained within an acoustically treated ply-
wood box, against the palm of the subject's right hand. A
pure tone was introduced into the transducer from a low
frequency audio oscillator at an input intensity of 100
decibels (re 0.002dyne/Cm2). The intensity level was
held constant during the course of the study. Frequency
was varied logariythmically. The test frequencies for
this study ranged from 10 to 2000 cycles per second.

Upon completion of the study the test frequencies
were divided into 50 cycle band widths. The total number
of responses obtained from the adult and adolescent groups
were tabulated for each 50 cycle band width. The

responses obtained for each band width were then compared

26

27

for the adult and adolescent groups only up to a
limit of 500cps.

The results of this comparison indicated no statisti—
cally significant difference between these groups except
in the l-50cps frequency range. A comparison of tactile
sensitivity within each group to sound stimuli of
selected frequencies was then made. Within the adult
group a statistically significant difference was obtained
for two of the three sets of frequencies tested. Within
the adolescent group a statistically significant difference
was obtained for each of the three sets of selected

frequencies tested.

Conclusions

 

In relation to age as a factor in the ability of
the skin to respond to changes in pure tone signals, there
seems to be little difference between the adolescents
and adults used in this study. The only significant
difference would be in favor of the adolescent group in
responding to low frequency pure tone signals in the 1-500ps
range. The greatest differences in cutaneous sensitivity
seem to occur within each group. In this respect the
adolescent group would seem to have a greater range in
cutaneous responses to pure tone signals than would the
adults. This, however, is still confined to the low

frequency ranges.

28

Within the framework of this study it seems
justifiable to make the following conclusions:

1. There is no significant difference in the
responses of adults and adolescents to changes in pure
tone frequencies introduced through the Skin, with
the exception of the frequency range of l-50cps.

2. There is a significant difference in tactile
sensitivity to selected pure tone frequencies within
the adult population.

3. There is a significant difference in tactile
sensitivity to selected pure tone frequencies within

the adolescent population.

Suggestions For Further Research

In considering the findings which have resulted
from this study there are several areas which may prove of
interest for further study.

Although the responses of the subjects used in this
study were to some extent reactions to just noticeable
differences in changes of frequency it is felt that a
more precise evaluation of responses to lower and higher
frequency ranges could be accomplished by the use of
equipment which would record the response of the skin
directly without involving overt reactions by the subjects.

Since intensity was one of the variables controlled

in this study it would be of interest to note the skin

29

response to frequency ranges which are presented at
different intensity levels.

The investigation of possible relationships be-
tween auditory and cutaneous responses to pure tone
signals may be of special interest particularly in the
lower frequency ranges where there seems to be more

sensitivity in cutaneous stimulation to pure tone signals.

APPENDICES

3O

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Test Frequencies l-2000cps for Adult Population.

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BIBLIOGRAPHY

Books

Békésy, Georg von. Experiments in Hearing; New York:
McGraw-Hill Book Co., 1960, 564-565

 

Mason, Russell E. Internal Perception and Bodily
Functioning. New York: International Universities
Press, Inc., 1961, 344.

 

Periodicals

 

Ahrens, R. S. "A Study of Vibratory Sensitivity,”
Archives of Neurology and Psychiatry, XIV (1925),

793-

Babkin, V. P., Rozen, O. M., Turmarkina, L. N., and Cherniak,
R. I. "The Study of Vibrational Sensitivity and the
Factors Influencing It," Biofizika, VI (1961), 61—67.

Békésy, Georg von. "Funneling in the Nervous System,"
Journal of the Accoustical Society of America, XXX

(1958): 399‘812.

Békesy, Georg von. ”Human Skin Perception of Traveling
Waves Similar to those on the Cochlea,” Journal of the
Acoustical Society of America, XXVII (1955), 830-841.

 

Birren, James E. "Vibratory Sensitivity in the Aged,"
Journal of Gerontology, II (1947), 267-268.

 

Geldard, F. A. "The Perception of Mechanical Vibration,”
Journal of General Psychology, XXII (1940), 281—289.

Geldard, F. A. ”The Perception of Mechanical Vibration: I
The History of the Controversy,” Journal of General
Psychology, I (1928). 320-352.

Gilmer, B. V. H. ”The Measurement of the Sensitivity of
the Skin to Mechanical Vibration,” Journal of General
Psychology, XIII (1935), 42-61.

 

AI;

Hawkes, G. R., and Loeb, M. "Vigilance for Cutaneous
and Auditory Signals," Journal of Auditory Research,
I (1961), 272-284.

Katz, K. "The Vibratory Sense and other Lectures," The
Maine Bulletin, XXXII (1930), 10.

 

Knudsen, V. 0. "Hearing with the Sense of Touch,”
Journal of General Psychology, I (1928), 320-352.

Pearson, G. H. J. "Effect of Age on Vibratory Sensibility,"
Archives of Neurolpgy and Psychiatgy, XX (1928),
482-496?

Rosenberg, Gilbert, and Adam, A. HEffect of Age on
Peripheral Vibratory Perception,H Journal of the
American Geriatrics Sociepy, VI (1958), 471-481.

Shewchuk, L. A., and Zubek, John P. ”Discriminatory
Ability of Various Skin Areas as Measured by a
Technique of Intermittent Stimulation," Canadian
Journal of Psychology, XIV (1960), 244-24 .

Wedell, C. H..and Cummings, S. B. Jr. "Fatigue of the
Vibratory Sense,” Journal of Experimental Psychology,
XXII (1938), 429-438.

Yacorzynski, G. H., and Brown, M. "Studies of the
Sensation of Vibration: Variability Threshold as a
Function of Amplitude and Frequency of Mechanical
Vibration," Journal of Experimental Psychology,
XXVIII (1941), 509-516.

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