Edward Bradford Titchener.

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tional, etc., as we please, by prearranging the conditions
under which the experiment is performed.

The reaction experiment consists, on its objective side,
in the accurate measurement of the time elapsing between


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320 Synthesis of Action, Reaction Experiment

the occurrence of the sensory stimulus and the execution
of the movement in response to it; on its subjective
side, in the introspective examination of the conscious
processes which run their course during this time, and
for some 2 sec. before it. The responsive movement
may follow at once upon the sensing of the stimulus, or
may be restrained until certain connections have been
formed in consciousness. In the former case we speak
of a simple^ in the latter of a compound reaction.

Fig. 10.

Method, — Figure 10 shows one of the sets of apparatus most
commonly employed in the reaction experiment. A and B are
different rooms : the reactor sits in the reacting room, B, the
experimenter, who notes the time taken by the reaction, in the
registration room, A, Reactor and experimenter are separated
in order that the reactor's introspection may be undisturbed by
noise, etc.

a is a telegraph key. The reaction movement employed
with this set of instruments consists in the lifting of the first or
second finger of the right hand from the button of the key. b is
a steel hammer (§ 29), the head of which can be lowered so as to

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§ 92. The Synthesis of Action 321

strike upon a steel block placed beneath it. The sound made
by the fall of the hammer is the stimulus to which the subject in
the present experiments is to react. ^ is a screen, which pre-
vents the reactor from seeing the hammer fall, and consequently
moving his finger too soon (reacting to sight, instead of to

Hammer and key are connected with an electric clock, or
chronoscope, e. The clock has two dials. A complete revolu-
tion of the hand of the lower dial occupies 10 sec, a complete re-
volution of that of the upper dial, ^ sec. The circumference of
each dial is divided into 100 parts ; so that the unit of measure-
ment on the lower dial is ^ sec, that on the upper, ^w^^ ^^^*
To read the time from the clock, therefore, we have only to add
the figures of the upper to those of the lower dial; if the lower
hand points to 76, and the upper to 25, the time is 7.625 sec.
The chronoscope goes only when the electric current is passed
through a magnet, which is attached to the clockwork.

The wires which connect together hammer, key and chrono-
scope run to the battery y^ by way of a com mutating key, d. The
function of this key is to change the direction of the current sent
through the chronoscope in successive experiments. In one ex-
periment, the current takes the direction "''"^ f^" ; in the next,
the direction +rX+~. This reversal is necessary, since a current
which travelled always in the same direction would permanently
magnetise the chronoscope magnet, and so alter the times recorded
by the dials.

Below the shaft of the hammer b is placed an electromagnet, g,
wires from which run to the battery/', by way of the commutator
(f. Closure of the commutator sends a current through the mag-
net, and the head of the hammer is thus pulled down upon the
steel block.

We will suppose now that an experiment is to be made. The
experimenter, seated before the chronoscope in the registration
room, closes the commutator d. Having done this, he signals to
the reactor (by means of an ordinary electric bell, not represented
in the Figure) to prepare for the reaction movement. The reactor


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322 Synthesis of Action, Reaction Experiment

lays his right arm on the table which carries the reacting key, «,
and rests the first or second finger of the right hand upon the but-
ton, thus closing the key. We have ( i ) a closed, d closed, and
b open. Two seconds after his signal (§ 41), the experimenter
closes the commutator ct ; the hammer falls. The sound stimulus
is thus given, while we have (2) a closed, ^closed, and b closed :
the chronoscope hands begin to move. The reactor, hearing the
hammer fall, raises his finger from the button of a, — /.<?., * reacts.*
We have (3) « open, b closed, and d closed : the chronoscope
stops with the breaking of the circuit at a. If the hands pointed
to 7.625 at (2), and the dials now read 7.819 at (3), we know that
the whole time, from the dropping of the hammer to the moving
of the finger, was .194 sec. This interval is called the 'reaction
time * ; and its unit, the thousandth of i sec, is called a * sigma'
(Greek <r).

While the experimenter is reading the reaction time firom the
dials of the chronoscope, the reactor writes out an introspective
account of his reaction-consciousness, beginning from the sound-
ing of the signal bell, 2 sec. before the hammer fell, and ending
with the snapping of the finger from the button of the reacting
key. Presently the signal is again sounded by the experimenter,
and a new experiment begins. It is customary to limit a series
of experiments to 15 or 20, since the strain of attention necessary
for reacting and for the subsequent introspection is very great, and
the reactor soon becomes fatigued (§ 10).

The psychological laboratories contain many forms of the re-
acting key, many kinds of instruments whose function it is to give
the stimulus which starts the reaction experiment, and many appa-
ratus for time registration. The responsive movement need not be
made with the finger ; it may be performed by lips, eyelid, vocal
organs, tongue, foot, etc. And the stimulus need not be auditory ;
it may be visual, tactual, etc. Moreover, the movement may be
movement not of a single finger, but of different fingers in dif-
ferent experiments : in such cases a five-finger key is employed.
And the impression may not be known beforehand to the reactor ;
it may be one of a number of colours, sounds, etc. : in such caser
the apparatus which gives the stimulus becomes very complex.

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§ 93- ^^^ Simple Reaction 323

The reaction time in the instance given above is the time
elapsing between the fall of the hammer and the movement of the
finger from the key. Within this time, the external stimulation
has made its way through the. ear, and the excitation set up in
the hair-cells of the basilar membrane has travelled to the brain.
Moreover, the outgoing excitation has run down the right arm, to
the finger-tip. No one of these physiological processes is accom-
panied by a conscious process. Plainly, then, the reaction time
is the duration of more than a simple action-consciousness : it is
the duration of this, plus the duration of certain physiological pro-
cesses. It is, unfortunately, impossible to measure the physiologi-
cal processes by themselves, and subtract the time which they
require from the total reaction time ; so that every recorded re-
action time is somewhat too long. This fact, while it does away
with the absolute value of the figures read from the chronoscope,
does not lessen their relative value. If a reaction time which in-
cludes, say, the formation of an association of ideas is longer than
a reaction time which does not, the difference may be referred,
other conditions being equal, to the association.

§ 93. The Simple Seaotion. — In the simple reaction
experiment, the movement follows at once upon the sens-
ing of the stimulus. In other words, the simple reaction
is an artificial impulsive action. But the impulsive action
of real life passes over into reflex action; and in like
manner the simple reaction, by a fitting preadjustment of
its conditions, may be brought very near to the reflex
type. We thus have two forms of simple reaction : the
true or impulsive form, or, as it is usually termed, the
' sensorial * reaction ; and the curtailed or reflex-like form,
usually termed the ' muscular ' reaction.

(i) The Sensorial Reaction, — \xi the sensorial reaction
experiment, the reactor is directed to hold his attention
from the outset upon the sensory stimulus, and to withhold
the reaction movement until he has sensed that stimulus.

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324 Synthesis of Action, Reaction Experiment

At the beginning of the experiment, therefore, conscious-
ness is dominated by an idea of end, and by a centrally
aroused sensation (or verbal idea) which corresponds to
the expected stimulus. When the stimulus is given, this
centrally aroused object-idea is replaced by the periphe-
rally aroused sensation, which brings with it the recogni-
tive or cognitive mood. We now have two of the three
factors in the impulse: the ideas of object and of end.
These are immediately supplemented by the idea of move-
ment, and the motor response to the stimulus is made.

The stages in the formation of the reaction-consciousness (sen-
sorial reaction) may, therefore, be tabulated as follows :

( i) idea of end plus anticipation of object ;

(2) idea of tndplus idea of object, with mood of * at home * or

' of course * ;

(3) idea of end plus idea of object plus idea of movement ;

(4) sensations set up by movement.

The idea of end soon ceases to play any considerable part in
the reaction-consciousness. At first it may be vividly present, as
the idea of gaining control over the attention, getting practice in
introspection, adding to the sum of psychological facts, doing a
piece of prescribed work well, etc. But with frequent repeti-
tion of the experiments, it loses its original definiteness, until, in
course of time, all that is left of it is the cognitive mood set up by
the sight of the reaction table, screen, etc.

The duration of the simple sensorial reaction differs
according to the sense department from which the object-
idea is taken, i.e., to which the stimulus appeals. This
time difference is, in all probability, due to the phyisiologi-
cal conditions of stimulation of the different sense-organs,
and accordingly has no psychological significance.

The sensorial reaction time has been determined in the spheres
of sight, sound, pressure, taste, smell and temperature. But the

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§ 93- ^^^ Simple Reaction 325

conditions of stimulation in the three last cases are so variable
and so little understood that the time measurements are of small
psychological value. For purposes of introspective analysis and
comparison, therefore, we must confine ourselves to reactions in
the domain of sight, sound and pressure.
The average durations are as follows :

(i) Sensorial reaction to light : 2700-;

(2) Sensorial reaction to sound : 225 cr ;

(3) Sensorial reaction to pressure : 2iocr.

(2) The Muscular Reaction, — In the muscular reaction
experiment, the reactor is directed to hold his attention
from the outset upon the movement which is to be made'
in response to the stimulus. At the beginning of the
experiment, therefore, consciousness is dominated by the
ideas of end and of movement. When the stimulus is
given, and the object-idea added to these two ideas, the
impulse is complete: motor response to the stimulus is
immediately made.

The sensorial reaction can never pass over into a reflex
action, since, by the conditions of the experiment, move-
ment cannot take place until the ideas of end and of
object have been supplemented by the idea of move-
ment. The muscular reaction, on the other hand, may,
in course of practice, come very near to the reflex type.
In the first place, the idea of end tends to disappear,
as the reactor grows accustomed to the experiment. In
the second place, the concentration of attention upon the
movement to be made paves the way for the actual move-
ment ; the attention does for this movement what biologi-
cal conditions have done for other movements which are
of the true reflex order ; there exists, for the time being, a
sort of ' reflex arc ' (§ 66) between the sense-organ to

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326 Synthesis of Actioft, Reaction Experiment

which the stimulus appeals and the muscles concerned in
the reaction movement, — just as there exists a permanent
reflex arc between, e,g,y the pressure organs in the cornea
of the eye and the muscles concerned in winking. Hence
it is intelligible that the muscular reaction should be quick
and spasmodic, and that it should oftentimes seem, when
introspectively examined, to have taken place automati-
cally, reflexly, without the intervention of any object-idea
at all.

When the reactor is new to the reaction experiment, the stages
in the formation of the reaction-consciousness (muscular reaction)
may be tabulated as follows :

( 1 ) idea of end plus idea of movement ;

(2) idea of tnAplus idea of movement plus idea of object ;

(3) sensations set up by movement.

But in its most reflex-like form, as performed by a highly
practised subject, the reaction is accompanied only by the follow-
ing processes :

( 1 ) idea of movement ;

(2) sensations set up by movement.

The idea of end lapses altogether, and the object-idea comes
to consciousness later, after the movement has been made.
The average durations of the muscular reaction are as follows :

(i) Muscular reaction to light : i8o<r ;

(2) Muscular reaction to sound : 1200- ;

(3) Muscular reaction to pressure : iio<r.

These times are too long to be pure reflex times : the winking
reflex occupies only about 500-. But they are reflex-like. This
is borne out not only by the verdict of introspection, but also by
the fact that the muscular reaction is not infrequently made too
soon, or made in response to the wrong stimulus. If the attention
has done its work thoroughly, and the * reflex arc * is well con-
nected in all its parts, there is a constant tendency for the move-

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§ 93- Tf^^ Simple Reaction 327

ment to ' go off * ; any slight provocation, such as the creaking of
a chair in the reacting room, is enough to bring about the jerk
of the finger from the key.

The difference between the average sensorial and the average
muscular reaction time amounts, as the tables show, to about
1 00 or or ^ sec. The difference is so constant that the experi-
menter, as he reads the figures from the chronoscope, can tell
whether the subject is reacting in the one way or the other.
This objective control is most valuable, since it enables us to
educate the reactor in introspection, to aid him in gaining sub-
jective control of his action by acquiring a mastery over the
attention (§97).

The Mean Variation, — If we are to estimate the introspective
power of the reactor, we must know not only the average duration
of his sensorial and muscular reactions, but the regularity or irreg-
ularity with which he reacts. Thus suppose that in three succes-
sive sensorial reactions to sound the chronoscope read iiocr,
3200- and 245 <r. The average of these three times is a good
average : 225 <r. But the irregularity is so great that the reactor
could not be credited with any considerable degree of control
over his attention.

Hence it is usual to record not only the average reaction time
of each reactor, but the mean variation of that time. By the
'mean variation* we mean the average difference between the
average reaction time and the single reaction times gained in
the course of an experimental series. Thus iioo- differs from the
average time (2250-) by 1150-; 3200- differs from it by 950-; and
245 <r differs from it by 200-. The mean variation in this case is
(115 +95 + 20) -5- 3 (the number of experiments in the series) ;
/>., 77cr.

The mean variation of a practised reactor is locr for muscular
reactions, and about 25 <r for sensorial.

The simple reaction experiment can be varied in many ways.
Thus we can investigate the influence of the intensity of stimulus,
of variation of the time allowed for preparation of the attention,

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328 Synthesis of Action. Reaction Experiment

of the omission of the signal, of the occurrence of distracting
stimuli, etc. The results of such experiments are all valuable as
throwing light upon the working of the attention.

§ 94. The Discrimination Beaction and the Cognition Re-
action. — In its sensorial form, the simple reaction is an
artificial impulsive action. In the experience of everyday
life, we have conflicts of impulses with one another, the
result of which may be inaction or selective action, and
conflicts of impulses with other groups of associated ideas,
the result of which may be inaction or volitional action.
Now if we can introduce these conflicts into the course of
the reaction experiment, we shall be able objectively to
measure and subjectively to examine the two most compli-
cated forms of the action-consciousness.

It is possible, by the help of the reaction method, to
put together an artificial selective or volitional action.
But the end cannot be reached by a single step. We
must advance to 'choice reactions,' as they are termed,
by way of the 'discrimination reaction' and the 'cognition

(i) The Discrimination Reaction, — The discrimination
reaction differs only in one respect from the simple senso-
rial reaction. In the latter, the subject reacts to a single
known stimulus; in the former, to one of two or more
known stimuli. The reactor is told, e.g.^ that he will be
shown either black or white, and that he is to react when
he has cognised the black as black or the white as
white ; but he does not know which of the two brightness
qualities to expect in each particular experiment. He has
to ' discriminate ' the stimulus which is actually employed.

(2) The Cognition Reaction, — The cognition reaction
differs in two respects from the simple sensorial reaction.

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§ 94- Discrimination Re action ^ Cognition Reaction 329

In the first place, the subject is required to react only
when he has cognised some one of two or more possible
stimuli ; the cognition reaction is a discrimination reaction.
In the second place, the reactor does not know, except in
a quite general way, what stimulus he is to expect. Thus
he may be told that he will be shown a light stimulus,
and that he is to react when he has cognised this stimulus
as a particular brightness or a particular colour; but nothing
more explicit is said.

If we wish briefly to characterise these three forms of reaction,
we may say that (i) the simple sensorial reaction involves cogni-
tion of one known stimulus, (2) the discrimination reaction in-
volves cognition of some one of a number of known stimuli, and
(3) the cognition reaction involves cognition of some one of a
number of unknown stimuli, — ' unknown,* that is, so far as igno-
rance is permitted by the conditions of the method at large.

For an analysis of the ' cognition * which is involved in each
case, </. § 72. The reader must remember that the titles ' discrim-
ination reaction * and * cognition reaction * are employed in narrow
and special senses. The ' discrimination reaction * implies a cog-
nition ; and the ' cognition reaction * implies a more elaborate dis-
crimination than does the ' discrimination reaction * technically
so called.

Both the discrimination reaction and the cognition reaction are
longer than the simple sensorial reaction. The time differences
between the latter and certain forms of the cognition reaction are
given in the following table :

The ' cognition * of a colour requires 300- ;

The 'cognition* of a printed letter requires 500-;
The 'cognition* of a short word requires 500-.

With simple stimuli, of this kind, there is hardly any difference
between the durations of the discrimination and cognition reaction.
The rule seems to be, however, that discrimination requires a
slightly shorter time than cognition.

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330 Synthesis of Action, Reaction Experiment

§ 95. The Choice Reaction. — The choice reaction is an
artificial selective or volitional action.

(i) The Choice Reaction as Selective Action, — This re-
action, in its simplest form, is a direct development from
the discrimination reaction. The reactor is told, e.g,, that
he will be shown either black or white, and that he is to
react only when he has cognised the black as black or the
white as white. So far, the directions are the same as
those for the discrimination reaction. But further, he is
to react to black by a movement of the right hand, and
to white by a movement of the left hand. This additional
direction introduces a conflict of impulses into the course
of the experiment.

(2) The Choice Reaction as Volitional Action, — This
reaction also is built up, in the first place, from the dis-
crimination reaction. The reactor is instructed as before,
except that he is told to react to black by a movement of
the right hand, and not to react to white at all. There is
thus introduced into the experiment a conflict between an
impulse and another group of ideas.

Both forms of the choice reaction, however, may be based
upon the cognition reaction, instead of the simpler discrim-
ination reaction. Thus the reactor may be told that he will
be shown a colour or a letter, and that he is to react by
naming the impression, i.e,^ by a movement of the vocal
organs. He is here left in entire ignorance as to what
colours or what letters will be exposed. The reaction will,
in this case, be an artificial selective action. Or he may be
told that he will be shown either a colour or a letter, and
that he is to react to the former by naming the given
impression, but not to react to letters at all. In this case,
the reaction would be an artificial volitional action.

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§ 95- ^^^ Choice Reaction 331

(i) It is plain that the time occupied by the conflict of im-
pulses in the first form of the choice reaction will depend very
largely upon the reactor's practice, and upon the number of
impressions used. If no more than two stimuli are employed, —
say, black and white, — the connection of black with right-hand
movement and of white with left-hand movement may become so
stable, in course of practice, that there is really no conflict of
impulses in the case. The reaction may come to be as much a
matter of course as the taking of a knife in one's right hand
and a fork in one's left (§ 96). On the other hand, if ten col-
ours are used, and the reactor instructed to reply to each colour
by the movement of a particular finger, there will nearly always
be some conflict of impulses, hovever great the amount of

The following may be taken as instances of the duration of the
choice reaction^ (selective action), {a) Nine persons were re-
quired to react to two intensities of sound by movements of the
two hands. The average time of the choice reaction was 3160-.
When we remember that the simple sensorial reaction to sound
occupies 2250-, and that the remaining 910- represents not only
the ' choice,' /.<?., the conflict of impulses, but also the ' discrimina-
tion,' /.<?., the cognition of the loud as * the loud ' and the weak as
*the weak' sound, we see that the conflict of impulses in the
experiments was not very serious. 'Choice' could not have
occupied more than 60 (t.

(b) In another investigation, ten persons reacted to ten impres-
sions (the figures i, 2, 3, 4, 5, I, II, III, IV and V) by movements
of the fingers of the two hands. The average time of reaction
was 6100-. If we subtract from this total 2700- for the simple
sensorial reaction time, we have a remainder of 340 a-. Allowing

1 The figures given here and later in the chapter must be regarded as quite
rough averages. The duration of a compound reaction varies so greatly with
variation of the experimental conditions, and conditions have varied so greatly
in the investigations as yet carried out, that it is very difficult to make any
general statement as to the time occupied by the processes of * choice ' and

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332 Synthesis of Action. Reaction Experiment

30-500- for * discrimination/ we have 290-3100- as the time
occupied by the conflict of impulses.

{c) We now come to the consideration of choice reactions
which presuppose not the * discrimination ' reaction but the * cog-
nition * reaction. Two persons reacted to colours, letters and
short words : the reaction movement consisted in the articulation
of the name of the given impression. The average times were :
for colours, 5500; for letters, 4100; for short words, 3900-.
From the first we must subtract 270 -|- 300 : the time occupied by

Online LibraryEdward Bradford TitchenerAn outline of psychology → online text (page 27 of 30)