tically significant (P<.001). The maximum

* information transmission for these sessions was

nearly 3.0 bits.

Mean amounts of information transmitted in
sessions that used unequal numbers of stridence
levels and durations are presented in Figure 2.
There appears to be a tendency for experienced
Os to transmit more information than naive
ones, and for performance to be more efficient
for identifications of stimulus combinations
with more durations (W.) than levels of
stridence (W,). The data of Figures 1 and 2
are combined in Figure 3 to illustrate general
trends, :

The results of an analysis of variance of the
data of Figure 2 are summarized in Table 1;
it is apparent that both the experience of O
and the amount of information available to O
significantly affect 1. The highly significant

* influence of the kind of stimulus combinations
presented indicates that performance is more
efficient for identification of duration than of
stridence (see Figure 2). None of the inter-
actions were statistically significant.

>
°
1

THEORETICAL MAXIMUM.

Sad
°
T

Ae wy
os Wp

O- -0 wy
NAIVE GROUP.
0-0 WD

1 1 ‘
4 8 2
NUMBER OF STIMULUS COMBINATIONS

expen. snour {

BITS OF INFORMATION TRANSMITTED
.
°

Ficune 2. Mean information transmitted when identify
ing combinations with either more stimulus intensities than
durations (W,) or the reverse (W,).

2 4.07
940 r rs
E E
z THEORETICAL MAXIMUM. 2 L
z , z
F g
= a
. 3.0-
23.of z*
2 2
FI Fi
z q z q
=
2 2
z EXPER. GROUP a——a 2
L 7 5 20,
S20 NAIVE GROUP O— 8
$ o
2 e
5 i 4 on Fi a. ran : :
4 8 V2 16 4 8 12 16
NUMBER OF STIMULUS COMBINATIONS NUMBER OF STIMULUS COMBINATIONS
i’ ‘
? 4

Ficune 1. Mean infSfmation transmitted when identify-
ing combinations with an equal number of stimulus
intensities and durations.

Ficuns 3, Mean information transmitted as a function of
the complexity and type of stimulus display.


SUMMARY

The number of possible absolute identifica-
tions of electrical cutaneous stimuli varying in
both stridence and duration was investigated
for both experienced and naive Os. In some
sessions, an equal number of stridencies and
durations were used; in others there were more
stridence levels than durations or the reverse.

Maximum transmission of information’ was

“with combinations of four stridence levels and

four durations. The channel capacity was
about 2.97 bits for the experienced Os and
2.76 bits for the naive ones. Experience was
not a statistically significant factor when an
equal number of durations and stridence levels
were used, In sesssions with unequal numbers
of durations or stridencies, experienced Os
transmitted significantly more information and
both groups were more efficient when identify-
ing combinations with more durations than
stridence levels.

Experienced Os identifying ~stimuli varying
in stridence or duration under conditions com-
parable to those of the present study have been

to transmit about 1.45 to 1.7 bits in
each of these (unidimensional) situations. The
value of 2.97 bits of this study was just a little
less than the simple sum of the performances
obtained with the dimensions used singly, but

’
i

it was also apparent that the dimensions are
not fully interchangeable.

REFERENCES

1. Alluisi, E. A., Conditions affecting the amount of in-
formation | in absolute judgments. Psychol. Rev., 1957,
, 97-103. :

2 Attneave, F., Applications of information th to
prychology. New York: Holt, (59, ont

3. Békesy, G. von., Experiments in hearing. New York:
McGraw-Hill, 1960,

4. Hartman, E. B., The Influence of practice and pitch-
distance between tones on the absolute indentification
of pitch. Amer. J. Psychol., 1954, 67, 1-14.

5. Hawkes, G. B., Absolute identification: of duration.
Percept, mot. Skills, 1961, 13, 203-209.

6. Hawkes, G. R., Cutancour discrimination of electrical
intensity. Amer. J. Psychol., 1961, 74, 45-53.

7. Hawkes, G. BR, and Warm, J. S, Maximum I, for
absolute identifications of cutaneous electrical intensity
Tevel. J. Paychol., 1960, 49, 270-288,

8. Hawkes, G. R. and Warm, J. S., AT for electrical
cutaneous stimulation. J, Ps: 1961, 51, 263-271.

9. McGrath, Lb Performance sharing in dual-mode
monitoring. Human Factors Res., Inc., Tech. Rep.
740-1, Los Angeles, Calif,, 1962,

10. Miller, CG. A., The magical number seven, plus or
minus two: some limits on our capacity for processing
information. Psychol. Rev., 1956, 63, 81-87.

11. Pollack, L, The information of elem: auditory
displays. Il. J. accust. Soc, Amer., i008, 28, 765-769.


).

much more difficult, especially for inexperi-
enced Os. In agreement with the results for
identification of stridence levels, use of a rela-
tively large physical range of stimulation re-
sulted in significantly better performance than
the use of a more restricted range, Relatively
minor changes in perceptual spacing engen-
dered by separation of the stimuli by an equal
number of jnds or by equal apparent sensation
magnitudes made no significant difference in
information transmitted,

Many investigators have reported that far
more than 3.0 bits may be transmitted if ad-
ditional dimensions are used in the stimulus
display. I, with multidimensional identifica-
tions has been reported to range from ap-
proximately 3.0 bits when identifying combina-
tions of pitch and loudness (11) to a very
large number of bits when attending to speech,
music, and other complex displays (2).

The present study investigated the channel
capacity for multidimensional identifications of
electrical cutaneous stimuli varying in both
stridence and duration. Based on the reduction
in efficiency found when identifying stimulus
durations presented at a weak rather than a
strong stridence level, particularly if inexperi-
enced Os are used (5), it was predicted that
performance in the multidimensional situation
would not be a simple summation of I, with
these dimensions used singly. Both jéxperi-
enced and naive Os were used. ,

METHOD *

The apparatus wis essentidlly the same as
that used previously (5), Alternating current
at a frequency of 100 cps was applied/to O
through a 12-mm, diameter electrode resting on

the index-finger pad; a 25-mm. diameter in-

active electrode rested on the palm. The in-
tenflty values of the stimuli were the same as
the extended rane values of Hawkes and
Warm (7), i.e., intensity levels eliciting pain
were included, Stimulus durations were the
“same as the extended range values used by
Hawkes (5), 50 to 1500 msec.

Group 1 consisted of five Os, all of whoii

had participated in two different experiments
involving absolute identification of electrical

cutaneous stimulus duration (5). A second
group of five Os had had no- prior experience
in studies involving absolute identifications.
Both groups participated in all phases of the
present investigation, and all Os were given
a familiarization session in which electrical
cutaneous stimuli were demonstrated in order
to avoid any possible complication from the
use of intensity levels eliciting pain. No
emotional or other difficulities were reported.

In three sessions, identifications were made
of stimulus combinations of equal numbers of
stridence levels and durations (2 x 2, 3 x 3, or
4 x 4), An additional six sessions were de-
voted to identification of stimulus combinations
with either more stridence levels than dura-
tions, or the reverse (2 X 3,3 2,2*4,4x 2,
3 x 4, 4 x 3). Order of presentation was
counterbalanced. In order to determine
whether or not errors in the 4 X 4 session could
be due to relatively close (perceptual) spacing
of the stimuli, in an additional session Os again
identified combinations of two stridencies and
two durations, In this tenth session, the stim-
ulus values were the same as the two middle
values used in the 4 X 4 session. In each
session, O was given a chart showing the num-
ber of stridence levels and durations to be used
in the particular session, and the code number
to be used to identify appropriately each com-
bination. All stimulus combinations used in
a given session were demonstrated prior to ab-
solute identification by Os.

‘

RESULTS

Figure 1 présefits mean amounts of informa-
tion transmitted: (I,) for those sessions involv-
ing equal numbers of stridencies and durations.
Note that none of the Os made errors’ when
+presented combinations of two stridence levels
and two durations. Further, none of the Os
made errors in the 2 X 2 session in which the
stimulus values were the same as the two
middle values of the 4 X 4 session. The data
on which. Figure I is based were tested by
analysis of variance to determine the influence
‘of Complexity (amount of information available
to 0), Experience, and the interaction of C x E.
Of these, only Complexity proved to be statis-

~. -2-


TABLE 1

Summary of Analysis of Variance of Information Trans-
mitted When Identifying Stimulus Combinations Containing
an Uneqnal Number of Durations and Stridence Levels.

Error

Source df MS Tem F P
1. Subjects (S) 8 8593 — — —
2. Complexity (C) 2 726427 13 3693 .001
3. Experience (E) 1 702002 1% 821 05
4. Weighting (W) 1 5980.02 12 27.06 001
5 CXE 2. .92047 Wo —- —
6&CxW 2 5927 10 —
TEXxW -1 375 WW _ _
&SxC 36 6 62553 100 _
92SxW 8 18713 1° — —
10 SxCxW 6 2799 — —~ —
i. Excxw 2 78860 — — _

Pooled Error Terms
12. 1049 240 22100 — —
13. 10+ 8 32 199673 — — ——
TABLE 2

Summary of Analysis of Variance of Information Trans-
mitted When Identifying Combinations of an Equal Num-
ber of Intensities and Durations.

Source df ‘SS MS F P
Between a 9 3362.69 1
Experience (E) 1 760.04 760.04
error (b) 8 2602.65 325.33
Within Ss 20 43662.68 1
Complexity (C) 2 38968.07 19484.04 74.69 .001
CxE 2 52046 260.23
error (w) 16 4174.15 260.38
Total 29 47025.37

i?
TABLES |

Information Transmitted (Bits) by Each O Identifyin
Combinations of Equal Numbers of Stridence Levels and
Subject Number of Stimulus Com

Experienced Group
4 2 16
1 2.00 265 326

2 2.00 2.80 3.05

3 200 2.45 278

4 2.68 2.80 2.76

ty 2.00 249 3.01

Mean = 2.00 264 297
& Naive Group

6 2.00 215 259

7 2.00 270 2.92

8 2.00 2.63 266

9 2.00 20 2.98

0 2.00 279 268

Mean 2.00 254 2.76

DO

TABLE 4
Information Transmitted (Bits) b;

Combinations of an Unequal Num
and Durations.

Subject Number of Stimulus Combinations
6 8

Each O Identi
of Stidence Level

2
We We

ve ° oo
W, we Wy,
7 Experienced Group

225° 258 %240 257 276 3.00
226 240 250 263 297 329
215 238 232 248 267 271
238 229 203 #278 256 275
226 222 195 248 267 264

Mean 226 237 224 259 273 288
Naice Group

6 193 228 220 213 240 24

7 205 250 230 268 239 286

8 217 216 294. 232 243 260

9 191 222 214 231 212 226

10 198 86258 «6232 «6213 239 251

Mean 201 235 224 231 234 251

* More Intensities Than Durations ‘
°° More Durations Than Intensities

we

Rm Oto

DISCUSSION AND CONCLUSIONS

Comparison of the results of the present
study to performance measures with unidimen-
sional stimuli indicates that information trans-
mitted (I) with multidimensional cutaneous
stimuli may be a little less than the simple sum-
mation of the I, for the dimensions used singly.
This is consistent with the results of other
studies reviewed by Miller (10). The mean
amount of I, in the most complex display of the
present investigation (a matrix of 4 stridence
levels x 4 durations) was 2.97 bits for the ex-
perienced group,, In previous studies of ex-
perienced groups, when Os were asked
to identify four durations, I, was about 1.45 bits
for stimuli presented at 1.6 db .(re: absolute
threshold), and: some 1.70 bits for stimuli at
6.0 db (5); this averages to about 1.58 bits per
stimulus duration. When four stridence levels
were presented for identification, I, was about
1.60 bits when immediate knowledge of results
was fumished, and 1.45 bits without such
knowledge, and the difference was not statisti-
cally significant. This averages to about 1.52 bits
per stimulus stridence, The simple addition of
these values, then, furnishes a predicted I, in
the multidimensional situation of about 1.58

~4~


ADZIS (34,
CARI

ABSOLUTE IDENTIFICATIONS
OF

CUTANEOUS STIMULI
VARYING IN

BOTH INTENSITY LEVEL

-- DURATION

__— ppneessinia art.

CLEARINGHOUS JAN 3:
FOR FEDERAL SCIENTIFIC AND:
TECHNICAL INFORMATION

| Hardcopy Microfiche

oe

SEPTEMBER, 1962


|

_ + 152 or 3.10 bits per stimulus combining
duration and stridence; the value of 2.97 bits
found herein is just a little below this value.
Some of the stimuli of the present study were
of a low stridence level, and it has been dem-
onstrated that duration identification becomes
less efficient when weak stimuli are presented
(3); on the basis of this, as well as Miller's
general conclusion, it would not be expected
that I, with combinations of stridence and
duration would equal or exceed the simple sum
of average I, values.

The significantly better performance when
identifying combinations that used a larger
number of durations compared to efficiency
with combinations having a greater number of
stridencies is of considerable interest, especially
since the total possible range of stridency was
used. Efficiency of performance when identi-
fying unidimensional stridence levels is approxi-
mately equivalent to that for stimulus durations
(5, 7). In those studies, stimulus separation
along these two, dimensions was. not greatly
divergent in terms of number of just noticeable
differences (jnds), and it has been found that
changes in stimulus separation on the order of
a jad do not affect K (see 5). It cannot be
concluded, however, that these two dimensions
are fully interchangeable on the basis of the
apparent simple summation of I, when these
two dimensions are combined, as discussed in
the preceding paragraph. ‘This number of jnds
for stridence (about 26 of so according to
Hawkes (6) is perhaps qhite limited when
compared to tlie possible; jnds for duration
(cf. 8), where a vastly greater physical range
of stimulation may be us

It is suggested that when Os are identifying
combinations with opportunity for a choice in
attention between duration and stridence, de-

dection of duration is easier and thus becomes

the preferred ,dimension, Békeésy (3) has
reported that there is a variation in apparent
area of cutaneous sensations as stimulus in-
tensity is changed. Further, some of the
intensity levels of the present study elicited
sensations of pain plus tingle, and others only
tingle. It is possible that some of these sensa-
tional variations may have affected identifica-
tions ‘in the present experiment, with the

variations being more closely correlated with
stridence than duration, McGrath (9) has
reported that when attention sharing is required
between two modalities in a vigilance task,
detection of easy signals improves while detec-
tion of difficult signals is unaffected or declines.
A similar mechanism might be operative when
Os are asked to identify cutaneous stimulus
combinations with an unequal number of
stridence levels and durations.

Békésy also has pointed out many similarities
between the operation of the auditory and
cutaneous nervous systems. Note in this con-
nection that although I, for identifications of
unidimensional stridencies or durations is less
than comparable performance with acoustical
stimuli, efficiency with stridence-duration com-
binations appears to be about the same as
reported by Pollack (11) for identifications of
patterns of pitch and loudness, about 3.0 bits.
In spite of (or perhaps because of) the rel-
atively primitive state of development of the
cutaneous nervous system, in some situations
it may be about as efficient as the auditory
apparatus.

This study indicates that the kind of stimulus
display used (in this case, use of more dura-
tions than stridence levels in the combinations
presented) can significantly increase the amount
of I. A previous study (5) indicated that the
perceived stridence can affect I, with duration
identifications, In previous studies of cutaneous
identifications, neither immediate knowledge of
results nor relatively minor changes in stimulus
spacing significantly affected transmission of
information, whereas relatively gross changes
in stimulus spacing resulting from manipulation
of the physical range of stimulation did signifi-
cantly affect channel capacity.

In addition to the conditions specified by
Alluisi (1) as influencing channel capacity in
a particular study, it may be concluded that
experience it in tasks of similar nature will have
a significant effect both in multi-dimensional
(as in the present study) and undimensional
absolute identifications (4, 5).

-5-—


in

ABSOLUTE IDENTIFICATIONS OF CUTANEOUS STIMULI
VARYING IN BOTH INTENSITY LEVEL AND DURATION

Sensory Psychology Section

. FEDERAL AVIATION AGENCY
AVIATION MEDICAL SERVICE
AEROMEDICAL RESEARCH DIVISION
CIVIL AEROMEDICAL RESEARCH INSTITUTE
OKLAHOMA CITY, OKLAHOMA
SEPTEMBER 1962



i
i

ABSOLUTE IDENTIFICATIONS OF CUTANEOUS STIMULI
VARYING IN BOTH INTENSITY LEVEL AND DURATION?

GLENN R. HAWKES, PhD.

INTRODUCTION '

Alluisi (1) has pointed out that the ‘amount
of information transmitted in absolute discrim-
inations will tend to be a maximum when there
is (a) equal perceptual spacing of the stimuli,
(b) an equal number of S and R categories,
(c) immediate knowledge of results, ang (d) a
maximum physical range of stimulation. Inas-
much as varying the physical range will serve
to limit the perceptual spacing possible with
a given number of stimuli, conditions (a) and
(d) above may be combined by use of, the
phrase “optimal spacing of the stinguli.”
Furthermore, variation of a parameter jn the
stimulus series other than that being judged
can affect information transmitted (5). In
addition, the experience of O has been shown to
be gf significance either with immediate knowl-
ege of results (4) or without such feedback
(5), and individual differences may be quite
marked (1).

For many unidimensional absolute identifica-

* tions, information transmitted (1,) typically
falls between 2.0 and 3.0 bits (10). Values less
than 2.0 bits have been found for identifications

1 Based on data recorded at the U.S, Army Medical
Research Laboratory, Fort Knox, Kentucky.

of cutaneous stimuli varying in stridence? (sub-
jective intensity of the tactual sensations) or
in duration, even under the optimal conditions
specified by Alluisi, Hawkes and Warm (7)
found in the identification of electrical stri-
dence levels, that I, reached a maximum of
about 1.7 bits when Os were furnished im-
mediate knowledge of results, Although the
gain in I, produced by providing knowledge of
results was not statistically significant in that
study, the use of a physical range of stimulation
including pain-eliciting intensity levels did yield
significantly better performance than restric-
tion of the range to lower levels. In the re-
stricted range situations, I, reached a maximum
of only 1.4 bits. Absolute identification of
electrical cutaneous stimulus duration was
, found by Hawkes (3) to result in I, of up to
1.9 bits. If only stimuli of low striderfce were
used, however, duration identifications became

2The word stridence was chosen to designate the subjec-
tive intensity of tactual sensations for the following
reasons: (2) it refers in to loudness (subjective in-
tensity of acoustic stimulation); (b) it also
roughness (a tactual sensation), a word which
to describe auditory sensations; (c) its use
relatively infrequent, but not rare; and (d) its sight and
sound is harmonious with vision and audi-
tion, namely, brightness and

in

-1-