Authors: Arthur Koestler
Janus (47 page)
AN EXPERIMENT IN PERCEPTION*Experience suggests that a common error in processing visual sequences is
Arthur Koestler and James J. Jenkins
The writers are indebted to Donald Foss for collecting and coding the data.
Thanks are also due to Professor Douglas Lawrence and Professor Ernest
Hilgard of Stanford University and to Professor Arnold Mechanic and
Joanne D'Andrea of California State College at Hayward for their generous
facilitation of the study.
ABSTRACT
inversion or transposition of two or more adjacent items. This phenomenon
suggests that information concerning the identity of items and their
positions may be partially separable. A perception experiment was performed
with tachistoscopic exposure of 5-, 6-, and 7-digit sequences. Abundant
evidence was found for transposition errors. Further, such errors were
distributed in a serial position curve much like that found for errors
of single items.
* See Chapter 1, 13, and p. 297. Reprinted with permission fromWhile information-processing in visual perception has received increasing
Psychon. Sci., 1965, vol. 3, pp. 75-6.
PROBLEM
attention in recent years
[1]
, one common phenomenon of faulty
processing which may have some theoretical significance seems to have been
ignored. We refer to the inversion (or transposition) of adjacent items
in a sequence of numbers shown in a tachistoscope. Though such errors are
common enough in bookkeeping and have earned a special proofreader's mark,
they are absent from discussions of visual perception or memory span in
standard works such as Osgood
[2]
and Woodworth and Schlosberg.
[3]
their correct sequence must either involve the
ordered
storage of
the individual items or the storage of information relating to that
order. Both information identifying an item and information defining
its place in the sequence must be available for the S
successful performance of the task.
not easy to demonstrate. If a subject makes a single error of identity,
reporting either an incorrect number or a blank, it may indicate that
he has lost only identity information. This argument, however, is
inconclusive, because if the subject had acquired no information at all
regarding the offending item, but complete information regarding other
items, the outcome would be the same. The inversion of two digits or
the permutation of three or more digits, on the other hand, furnishes
a compelling argument because it is
prima facie
evidence that the
identity information is accurate while the positional information is
incomplete or distorted.
of transposition could be observed under laboratory conditions and to
describe the locus of its probable occurrences in a given sequence.
METHODThe stimulus materials were 80
4x6
notecards upon which digit
sequences were typed in elite type. The 80 sequences were divided into
four sets of 20 cards each. The first set showed sequences 5 digits in
length; the second and third sets showed 6-digit sequences; the fourth set
showed 7-digit sequences. The sequences contained the digits
1-9
with never more than a single digit repeated on a given card. The repeated
digit, if any, never occurred without at least one intervening digit. The
sets were presented in the order given above. A random arrangement was
made of each set. This arrangement was used in the forward order for
half the Ss and in reverse order for the remainder. The materials were
presented in a mirror-type tachistoscope.
The S held a plunger switch which activated the tachistoscope.
The E
in place. The S activated the tachistoscope when he was ready. He
was instructed to say the digit sequence aloud immediately after its
appearance, and was encouraged to guess if he was not sure of one or
several items. The S always knew how many digits were shown. Responses
were recorded on a tape recorder. Only one exposure per sequence was
given and the S was not given any information about the correctness of
his response.
Two practice sequences with ascending limits were given to accustom the S
to the apparatus and to provide the E with some information on threshold.
The test sets were then presented. One-minute rest periods were given
after each set.
Exposure duration was individually adjusted for each S. Pilot work
suggested that transpositions occurred most readily at the point where
the S was beginning to miss single digits in the sequence. Therefore,
the E attempted to have the exposure interval long enough that the proper
number of digits would be reported but short enough that they were not
always reported with complete accuracy. After every five cards the E
decided whether to keep the exposure the same or to change it. Since there
were practice effects in the task and since the task became appreciably
more difficult, E continued to modify the presentation time during the
course of the experiment. Generally 10-msec steps were employed in such
changes but with an occasional S whose performance was markedly inferior
the step span was increased.
RESULTS AND DISCUSSIONResponses were transcribed from the tape and scored. The following categories
were employed:
C -- correctResults are given in terms of these scoring categories in Table I.
E -- gross error
I -- one digit incorrect, or 'blank' reported for a single missing digit
T -- transposition of adjacent pairs of digits with rest of
sequence correct
T1 -- transposition of three or more digits with remainder correct
IT -- transposition of two or more digits and one digit incorrect
O -- other errors, usually experimental or equipment errors
Examination of the table shows that transposition provides an important
source of errors. It is, however, difficult to find a statistical model
which would provide a precise evaluation of the statistical significance
of such errors. As Woodworth and Schlosberg
[4]
point out in
their discussion of scoring memory span, any scoring system which attempts
to provide separate credit for accuracy and order is arbitrary. Thus,
any statistical model must make assumptions about the S's strategies
on the one hand (e.g., Did the S note that digits can repeat within
a sequence and, if so, did this alter his guessing behaviour in the
appropriate manner?) and the interrelationships of error types (which
we do not yet know) on the other. Fortunately, the question is not
crucial for present purposes. The only question that need be asked here
is whether there is more transposition than would be expected by chance
(however chance is to be defined).
Table I. Distribution of Responses by Categories for Each Stimulus SetWe think the answer to that is clear. Of the 140 errors on the 5-digit
(280 items)
---------------------------------------------------------------
Scoring code 5 digits 6 digits 6 digits 7 digits
---------------------------------------------------------------
C 130 60 65 12
E 21 67 47 122
I 50 43 50 21
T 23 23 32 12
T1 2 14 5 9
IT 44 64 73 96
O 10 9 8 8
---------------------------------------------------------------
sequences, 69 involve transpositions; of the 211 and 207 errors on the
6-digit sequences, 101 and 110 respectively contain transpositions; of the
260 errors on the 7-digit set, 117 contain a transposition. It is evident
that until the task becomes exceedingly difficult (and the response
unscorable), approximately half the errors involve transpositions.
No reasonable 'guessing' or chance model we have contrived can account
for this finding. It seems simplest to conclude that in a large portion
of the errors the S has the correct information as to the identity of some
of the digits but has lost the information as to their precise location.
As a first step in describing the phenomenon, the distribution of errors
over positions was obtained for the simplest errors of both types. Table
II shows the location of the error for each instance when one digit was
incorrect (I error). Table III gives the location of the pair of items
transposed when only single transposition was observed (T error). It can
be seen that both sets of distributions for all sequence lengths show the
same serial position effect, suggesting that both kinds of error are
susceptible to the same form of interference. If one has all the individual
items, he is least likely to have precise position information in the latter
half of the sequence. Conversely, if one lacks the identity of an item,
it is most likely to be one from a position in the latter half of the list.
The most probable transposition for any particular length of sequence
appears to involve the inversion in order of the item in the most difficult
position in the sequence and the item immediately preceding it.
The psychological nature of each kind of error is not at all clear but it
seems likely that future work will help narrow the alternatives. It would
be particularly interesting to know, for example, whether transposition
is equally common when the experiment is conducted with Sperling's procedure
or with a rapid sequential procedure such as that used in short-term memory
research.
While we cannot at present make any decision as to the underlying nature
of the transposition phenomenon, we feel that this experiment concurs
with common experience in pointing to a pervasive distortion in the
visual perception and reporting system which theories of information
processing must take into account.
Table II. Position of Errors in Cases of a Single Incorrect DigitAPPENDIX III
Position
-------------------------------------
Sequence 1 2 3 4 5 6 7
--------------------------------------------------
5-digit 1 1 4 34 10 - -
6-digit 0 2 1 4 31 6 -
6-digit 0 1 3 11 25 10 -
7-digit 0 0 2 0 7 8 4
--------------------------------------------------
Table III. Position of Transposed Digits in Errors Involving a
Single Transposition
Positions transposed
Sequence 1-2 2-3 3-4 4-5 5-6 6-7
5-digit 0 2 18 3 --- ---
6-digit 0 2 1 17 3 ---
6-digit 0 5 1 21 5 ---
7-digit 0 0 0 3 7 2
NOTES ON THE AUTONOMIC NERVOUS SYSTEM*In general (but there are, as we have seen, important exceptions) the action
* See p. 140.
of the two divisions is mutually antagonistic: they equilibrate each other.
The sympathetic division prepares the animal for emergency reactions
under the stress of hunger, pain, rage and fear. It accelerates the pulse,
increases blood pressure, provides added blood-sugar as a source of energy.
The parasympathetic division does in almost every respect the opposite:
it lowers blood pressure, slows the heart, neutralizes excesses of
blood-sugar, facilitates digestion and the disposal of body wastes,
activates the tear glands -- it is generally calming and carthartic.
Both divisions of the autonomic nervous system are controlled by the
limbic brain (the hypothalamus and adjacent structures). Different authors
have described their functions in different terms. Allport
[1]
related the pleasurable emotions to the parasympathetic, the unpleasant
ones to the sympathetic. Olds
[2]
distinguishes between
'positive' and 'negative' emotive systems, activated respectively by
the parasympathetic and sympathetic centres in the hypothalamus. From a
quite different theoretical approach, Hebb also arrived at the conclusion
that a distinction should be made between two categories of emotion,
'those in which the tendency is to maintain or increase the original
stimulating conditions (pleasurable or integrative emotions)' and 'those
in which the tendency is to abolish or decrease the stimulus (rage,
fear, disgust)'.
[3]
Pribram has made a similar distinction
between 'preparatory' (warding-off) and 'participatory' emotions.
[4]
Hebb and Gellhorn distinguish between an ergotropic
(energy-consuming) system operating through the sympathetic division
to ward off threatening stimuli, and a trophotropic (energy-conserving)
system which operates through the parasympathetic in response to peaceful
or attractive stimuli.
[5]
Gellhorn has summarized the
emotional effects of two different types of drugs: on the one hand the
'pep pills', such as benzedrine, and on the other the tranquilizers,
such as chlorpromazine. The former activates the sympathetic, the
latter the parasympathetic, division. When administrated in small
doses, the tranquillizers cause 'slight shifts in the hypothalamic
balance to the parasympathetic side, resulting in calm and contentment,
apparently similar to the state before falling asleep, whereas more
marked alterations lead to a depressive mood'.
[6]
The
benzedrine-type drugs, on the other hand, activate the sympathetic
division, cause increased aggressiveness in animals, and in man in small
doses alertness and euphoria, in larger doses over-excitation and manic
behaviour. Lastly, Cobb has summed up the implicit contrast in a pointed
form: 'Rage is called the most adrenergic, and love the most cholinergic
characteristically parasympathetic reaction'.
[7]
What this short survey indicates is, in the first place, a general trend
among authorities in this field to distinguish between
two basic categories
of emotion
-- though the definitions of the categories differ. In the second
place, there is a general feeling that the two categories are correlated to
the two divisions of the autonomic nervous system.
APPENDIX IV
UFOs: A FESTIVAL OF ABSURDITY*
* See above, Chapter XIV.There is an understandable, but questionable connection in the public's
mind between CETI (communication with extraterrestrial intelligence)
and UFOs (unidentified flying objects, vulgarly called flying saucers).
At the CETI conference in 1971*, UFOs were only mentioned in passing, and
none of the participants suggested that they were of extra-terrestrial
origin. The main reasons for this scepticism were summed up by the
astrophysicist Carl Sagan:
Such [advanced extraterrestrial] civilisations will be inconceivablyThe words that I italicized refer -- as the context indicates -- to the
in advance of our own. We have only to consider the changes in
mankind in the last 104 years and the potential difficulties
which our Pleistocene ancestors would have in accommodating to
our present society to realize what an unfathomable gap 108 to
1010 years represents, even with a tiny rate of intellectual
advance. Such societies will have discovered laws of nature
and invented technologies whose applications will appear to us
indistinguishable from magic. There is a serious question about
whether such societies are concerned with communicating with us,
any more than we are concerned with communicating with our Protozoan
or bacterial forebears. We may study microorganisms, but we do not
usually communicate with them. I therefore raise the possibility
that a horizon in communications interest exists in the evolution
of technological societies, and that a civilization very much more
advanced than we will be engaged in a busy communications traffic with
its peers; but not with us, and not via technologies accessible to
us. We may be like the inhabitants of the valleys of New Guinea
who may communicate by runner or drum, but who are ignorant of the
vast international radio and cable traffic passing over, around and
through them [my italics].'
* See above, p. 282a.
hypothesis that UFOs may be space-vehicles, or automated probes released
from larger mother-ships (like the landers released from the Viking
orbiters). In spite of the aerial acrobatics which they are reported
to perform, the appearance and behaviour of UFOs is too close to
'technologies accessible to us' to qualify as fit for magicians. As to
the argument that we are too primitive to be worthy of study, one could of
course object that our ethologists and anthropologists do not share this
arrogant attitude towards lowlier forms of life and culture. But there is
again a counter-argument: if our galaxy is as brimful with life as the
astrophysicists tell us, then there must be some system of priorities
for the magicians' exploratory survey-programmes, and even among lowly
civilizations we may not be of special interest. If, on the other hand,
we are as interesting as our terran chauvinism whispers into our ears,
then why do UFOs so studiously avoid contact with us, by radio, or lasers
or holographs -- not to mention some advanced techniques of ESP? Evasion
of contact is indeed the chief characteristic and common element in the
antics of flying saucers. And as for the few cases in which contact with
'humanoid' UFO passengers is alleged, they represent, as one eminent
ufologist wrote, 'a veritable festival of absurdity'. [2]
Why, then, bring up this disreputable subject at all? Firstly, because it
seems to me that it would be cowardly, after discussing extraterrestrial
civilizations, to pass over UFOs in silence -- although, as I said,
the two subjects may be unconnected. In the second place, UFOs --
unidentified (or unexplained) flying objects as distinct from IFOs
(identified flying objects) do seem to exist, whatever their origin.
This belief is apparently shared by nearly a half of American astronomers.
The following extract is from an article in the
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