METHOD OF AVERAGE
ERROR
By
Navdeep Batth
Lecturer
D.A.V. College For Girls
Yamuna Nagar
• It is one of the oldest and most fundamental method.
• The aim of the method is to determine equal stimuli by
active adjustment .
• Observer is provided with standard stimulus (Ss)
• Variable stimulus (Vs) is also provided.
• Variable stimulus is greater or less than standard
stimulus
• Observer adjusts variable stimulus until it seems
equivalent to standard stimulus.
• Number of such judgements are obtained from
observer.
OTHER NAMES
• Method of reproduction
• Method of adjustment
• Method of equivalent stimuli
ORIGIN OF THE
METHOD
• According to Titchner “ the method is free
gift to psychophysics from the exact
sciences of physics and astronomy.”
• Fechner introduced this method into
psychophysics .
• Used for visual and tactual
measurements.
AN EXPERIMENT OF
MULLER LYER ILLUSSION
• Variable stimulus is the line with feathers or feather
headed line
• Standard stimulus is a arrow headed line
• In half of the observations variable stimulus should
be on observer’s left and on right in other half.
• These two space arrangements are denoted
as L and R.
• The trial should start with variable stimulus
obviously too great so that the movement of
the terminal arrow is inward.
• In other half variable stimulus variable
stimulus is set obviously too small so that
the movement is outward.
• This is denoted by I and O
• There are consequently four possible
combinations of condition RO, RI, LO and LI.
• Counterbalancing is followed within each
set of trials.
• Experimenter should randomize the
setting among large, medium and small
starting length for variable stimulus.
DESIGN OF THE
EXPERIMENT
Sr.No
R
L
R
L
I
O
O
I
I
O
O
I
1
11
9
10
9.2
8.8
13.5
13.5
13.4
2
9.8
9.4
9.3
9.7
13.6
14.4
13.9
14.6
3
10.2
9.5
9.5
10.2
13.7
15.2
14.7
15
4
10
9
9.2
9.5
14.3
14.2
14.3
14.9
Mean
10.25
9.22
9.5
9.65
12.6
14.32
14.1
14.47
• RLRL design is used.
• This is used to control space error.
• IOOIIOOI design is used to control
movement error.
• If the mean of the judgment is greater than
variable stimulus and difference is positive.
• This shows that feather headed line is
overestimated.
• Arrow headed line has been underestimated.
• There are other constant errors.
• CONSTANT ERROR OF SPACE
• Mean of all right trials – Mean of all left trials
2
Mean of all right trials = 48.04 = 12.06
4
Mean of all Left trials = 46.07 = 11.51
4
12.06 – 11.51 = 0.49 = 0.24 cm
2
2
• CONSTANT ERROR OF MOVEMENT
• Mean of all Inward trials - Mean of all outward trials
2
Mean of all Inward trials = 46.97 = 11.74
4
Mean of all Outward trials = 47.14 = 11.78
4
= 11.74 – 11.78
2
= - 0.04 = - 0.02 cm
2
• PRACTICE/FATIGUE EFFECT
Mean of first 50% trials – Mean of last 50% trials
2
Mean of first 50% trials = 38.62 = 9.65
4
Mean of last 50% trials = 55.49 = 13.87
4
= 9.65 – 13.87
2
= - 4.22 = - 2.10 cm
2
• POINT OF SUBJECTIVE EQUALITY• It is the point where participant/subject
perceives arrow headed line equal to feather
headed line
• PSE = Mean of all the trials
8
= 94.11 = 11.76 cm
8
• CONSTANT ERROR
PSE – Standard stimulus
=11.76 – 15
= - 3.24 cm
DETERMINATION OF DL
• Probable error is calculated.
• Standard deviation from PSE value is
measured.
• Standard deviation is calculated from PSE
value.
• Standard deviation is multiplied with a
constant value i.e. 0.6475
ADVANTAGES
• This method has practical advantage of
economizing the time of both E and O.
• This method is useful when number of
measurements are to be made in a limited
time.
• This method is “most natural” of all methods.
• The observer participates actively in the
judgement.
DISADVANTAGES
• Perceptual Vs Motor errors
• Constant time error
• Other uncontrolled errors
APPLICATIONS
• It applies in those cases where observer can
manipulate the variable stimulus.
• Applied where variable stimulus is constantly
variable.
• Most useful application in study of visual extent.
• It has been used in the study of visual intensities.
• Used in study of tonal attributes, pitch and
intensities.
• It has been adapted to the study of bodily
movements.
• It can be adapted to certain problems in
memory.
Method OF CONSTANT
STIMULI
• It is most accurate and widely applicable method.
• They are employed in the measurements of
stimulus limens, differential limen equal sense
distances and equivalent stimuli.
• The difference between this method and method
of constant stimuli is that the stimulus is
presented in random and quasi random fashion.
• This eliminates error of habituation and error of
anticipation.
OTHER NAMES
• METHOD OF CONSTANT STIMULUS
DIFFERENCE- The same comparative stimulus
are compared with standard stimulus.
• FREQUENCY METHOD – As the frequency of
each stimulus value to be presented to the
participant is same.
• The experimenter presents the stimuli which
lie in the transition zone.
• Experimenter uses the stimuli which lie in the
range between those which can always be
perceived and those which can never be
perceived.
• Limited range is used because in each trial all
the stimulus values have to be presented.
DETERMINATION OF AL
• Determine the range of stimulus values –
• The stimulus that is perceived just above zero
percent of the trials.
• The one that is perceived little below hundred
percent of the trials.
• This is selected as range to be employed.
• Selection of stimulus values –
• Experimenter selects few stimulus values from
the range .
• Some above and some below tentative AL.
• Spacing stimulus values at equal intervals –
• The stimulus values are placed at equal
intervals on stimulus continuum.
• Number of trials are determined –
• For the experiment 10 trials are determined.
• Number of trials should be determined before
beginning with the experiment.
• Presentation of stimulus in random order –
• Stimulus values should be presented in random
order.
• Various randomization techniques can be used.
•
•
•
•
Slip method.
Random number tables.
Flip of coin
All stimulus values should be presented equal
number of times.
DETERMINATION OF AL
• Let us take the ordinary two point tactual
threshold.
• Region on the skin is selected on which the
limen is to b determined.
• E makes some preliminary trials with compass
points or asthesiometer.
• Transition zone is roughly determined.
• Some judgements are “two” and some are
“one”.
• Experimenter selects five stimuli such that the
middle one is probably close to the limen.
• The smallest stimulus is likely to give report of
“two” about 5% of the time.
• The largest stimulus to give report of “two” 95%
of the time.
• The stimulus intervals are equal.
• Experimenter then applies the stimulus in
random until each stimulus has been applied
equal number of times.
• The data from which the limen is to be
computed consist of the proportion of the
time each stimuli receives the judgment
“two”.
HYPOTHTICAL DATA
Stimulus
(in cm)
1
2
3
4
5
6
7
8
9
10
%
(2)
p
%
(1)
p
5
2
2
2
2
1
2
2
2
2
2
90
.9
10
.1
4.5
2
2
1
2
1
2
2
2
2
2
80
.8
20
.2
4
2
1
2
1
2
2
2
2
2
2
80
.8
20
.2
3.5
2
2
2
1
2
2
1
1
2
2
70
.7
30
.3
3
2
1
2
1
2
2
1
2
2
1
60
.6
40
.4
2.5
1
1
1
1
2
2
1
2
2
1
40
.4
60
.6
2
1
1
1
2
1
1
1
1
1
1
10
.1
90
.9
• THE INTERPOLATION METHOD• The two point limen is that separation of two
points that yields 50% judgment of “two” and
50% judgment of “one”.
• In the data 50% judgment of 2 responses lie
between 40% to 60%.
• AL is in between 3cm and 2.5 cm.
• AL is computed by difference between 3cm
and 2.5cm.
•
THE PROPORTION METHOD –
• AL = sl+ (sh – sl) (.5 –pl)
ph – pl
•
Where,
sl = stimulus immediately lower than the limen.
sh = stimulus immediately higher than the limen.
ph = proportion of “two” for the stimulus
immediately higher than the limen
pl = proportion of “two” for the stimulus
immediately lower than the limen
• AL = 2.5 + ( 3 – 2.5) (.5 – .4)
.6 - .4
= 2.5 + (0.5) (.1)
0.2
= 2.5 + 0.05
0.2
= 2.5 + 0.25
= 2.75 cm
DETERMINATION OF DL
• This requires the addition of a standard stimulus.
• On each trial a pair of stimuli and one of the
variable stimuli are presented to subject.
• Subject judges whether one member of the pair
is “greater than” or "less than” the other or
middle category such as “equal” or “doubtful”
• Experiment begins with determining DL for lifted
weights.
• Three category judgment is done.
• The standard weight is of 50 gm.
• The variable weights range from 40 to 60 gm.
• Observer lifts the standard weight (50 gm) first
and variable weight after that in half of the trials.
• In other half of the trials variable weight is lifted
prior to the standard weight.
• He renders judgment always with respect to the
second stimulus reporting it “greater”, “less” or
“doubtful” as compared with the first.
DATA FROM LIFTED WEIGHT
EXPERIMENT
Stim
ulus
1
2
3
4
5
6
7
8
…20 +
=
-
60
+
+
+
+
+
+
+
+
+
20
0
0
58
+
+
+
+
+
+
+
+
+
20
0
0
56
+
+
+
+
+
+
=
+
+
18
2
0
54
=
+
+
=
+
+
+
+
+
15
5
0
52
=
+
=
=
=
+
+
+
+
10
7
3
50
=
=
=
=
=
=
+
+
+
8
10
2
48
=
=
-
=
=
=
=
=
=
6
10
4
46
=
-
-
-
-
=
=
-
-
2
8
10
44
-
-
-
-
-
=
-
-
-
0
1
19
42
-
-
-
-
-
-
-
-
-
0
0
20
40
-
-
-
-
-
-
-
-
-
0
0
20
UT
55
51
51
53
51
51
49
47
49
LT
45
47
47
47
47
43
43
45
47
• Upper threshold (UT)
• UT = Sl + ( Sh – Sl) ( .5 – Pl)
( Ph – Pl)
• Lower Threshold (LT)
• LT = Sl + ( Sh – Sl) ( .5 – Pl)
( Ph – Pl)
• IU = UT – LT
• DL = IU
2
• PSE = UT + LT
2
CE = PSE – standard stimulus
ADVANTAGES
• It is a versatile method and has broad range of
applicability.
• Limens can be determined accurately.
• Computational processes are very refined.
• Experimental errors as found in method of
limits are avoided.
DISADVANTAGES
• The method is not as economical as other
methods.
• Various kinds of biases in judgment can be
there.
THANK YOU