Determination of equal stimuli by the Method of Average Error

Problem: The purpose of this experiment is to determine the extent of visual illusion in the

Muller-Lyer illusion apparatus by using the method of average error.

Material Required: Muller-Lyer illusion apparatus, paper and pencil.

Procedure: The experimenter in advance should prepare observation table in record book for

noting down the judgements.The table should have two space and two movement conditions with the sequence of RO, LI, LO, RI, LI, RO, RI, and LO. The experimenter should give the following instructions: “Look at this board, there are two lines. These two lines as you see are unequal in size. I will keep the length of this line as constant and go on varying the length of variable line in small units, either increasing or decreasing. At every step you should tell me whether SV is equal to SS or not. When you feel they are equal, I will stop”.

Result: In all, there are 4 ascending series (RO, LO, RO, LO) and 4 descending series (RI, LI,

RI, LI). Thus, we have eight conditions. The means for R and L spaces and means for O and I movements have to be worked out. The main aim of this experiment is to determine the discrepancy between the SS (arrow heads) line and the average of the subject’s judgements(Mj). This is the extent of illusion. This is the main constant error(Ec) of the experiment.

The formula to find out space error is : Mr-Ml/2 ;

Mr = Mean of the right space Ml = Mean of the left space The formula to find out the movement error: Mo-Mi/2;

Mo = Mean of outward movement Mi = Mean of inward movement The formula to find out constant error is : Mj-SS= Ec

Mj = Mean of all judgements SS = Standard stimulus Ec = Constant error

Discussion: Discuss the results obtained in Muller-Lyer illusion experiment. State the extent of

illusion whether it is due to to overestimation or underestimation. State whether the result is in accordance to the assumption of the experiment. The SS line should be underestimated in comparison with the SV. Compare the space and movement error and state which is greater and why. Is the constant greater than the space and movement error, if so, why? Any variation in the subject’s judgement in the ascending series from the descending series has also to be explained. Ø Memory Experiments (STM/LTM)

Short Term Memory (STM) is a working memory that serves as a transfer station between both input from our outside environment and output from our inner environment. For eg., we remember a telephone number we have looked up long enough to dial it. It has been identified with primary memory of William James (1890), who defined primary memory as the contents of the consciousness and the psychological present.

STM differs from long term memory (LTM) in three ways. First, items initially stored there are fragile and easily forgotten. Second, relatively few items(three to seven) can be stored there, so STM is of limited capacity. And third, the coding format of items stored in STM seems to be predominantly acoustic or articulatory in nature. In contrast, LTM retention is more permanent, has an apparently unlimited capacity, and stores items in a primarily semantic format.

In order to trace out the time course of forgetting from STM, it is necessary to prevent rehearsal. This is because rehearsal is generally held to be the primary vehicle for maintaining information in STM and transferring information to LTM. STM is of limited capacity, and has been variously estimated as seven+ – two, when its capacity is measured by memory span experiments (Miller,

1956), and as few as four to five items when its capacity is measured by the number of letters we

can report from a brief visual exposure (Sperling, 1960).

Unless the new material is simple, we need rehearsal to keep in STM. In rehearsal the information or task is practiced in one way or the other, overtly or covertly. The event is simply repeated several times. The aim here is merely to keep the material available until it can be used, or until it can be stored in some integrated manner.

The importance of rehearsal was demonstrated when experimental subjects were unable to remember a single nonsense syllable for just a few seconds. The experimenter presented them with a three letter syllable followed by a number. Each subject observed the word visually, and then to prevent rehearsal, was required to count backward by 3 or 4 from a randomly selected three digit number. When the subject was asked the syllable three seconds later, it was repeated correctly only about half the time. With successively more counting, recall continued to decline, and after 18 seconds, less than ten percent of the syllables were recalled (Peterson & Peterson,

1959).

Experiment: Paired-Associate Learning: Immediate memory span(non-sense syllable)

Problem: To measure the immediate memory span for an individual using the method of paired-

associate learning for non-sense syllable.

Material: A list of non-sense syllables not less than 10 (in a pair, there should be two non-sense

Procedure: The experimenter should have made all the preparations before hand. The pairs of

non-sense syllables should be neatly typed or written with sufficient space between the two, so that it is legible to the subject. The list should be pasted in the rotating drum having full visibility of the two syllables in the window. The drum should be adjusted in such a way that the pair of non-sense syllables should be exposed only for two seconds.

After the preparations, the following instructions have to be given to the subject: “Please look at the small window of the drum (showing it). You will see two non-sense syllables together in a line with a hyphen between them. The first word is the stimulus and the second is the response. I will present them in pairs only for a period of two seconds. I will show you ten such pairs. You will have to observe each pair carefully and learn to associate with them. After presenting all ten pairs of these non-sense syllables, I will stop it for a few seconds. Then I will show you only the first syllable of the pair. Then your task is to produce the corresponding response syllable of that particular stimulus. As soon as you see the first stimulus or the first syllable of the pair, you at once call the response syllable within two seconds before the appearance of the second stimulus. If you have any doubt, you may ask me”.

The experimenter at once should start the memory drum to move step by step for two seconds exposing a pair of syllables at every step. When all the ten pairs are presented, the experimenter should stop for a period of six seconds and then start presenting the stimulus of each pair alone. The subject at once should recall the response for the stimulus. After presenting all the ten stimulus syllables alone, the experimenter should take the introspective report from the subject and send the subject. If the experimenter has asked the subject to write down the responses on paper, then he should collect the paper from the subject.

Results:

l The experimenter will analyse the responses and find out correctly associated response syllables

l The results may be presented in a tabular form as shown below:

Sl. No. (1) 1 2 3 4 5 6 7 8 9 10 Paired-associate and the stimuli

(2) XEW-MNK CIL-GOF LHE-KAM ZSW-XPJ FXC-BKE QJY-LIX MEG-HGI DUV-BXT SEK-WKl JOX-UTR Stimulus Syllable (3) XEW CIL LHE ZSW FXC QJY MEG DUV SEK JOX Response syllable by the subject (4) Result (5)

l The number of correct stimulus-response associations may be taken as the immediate memory span

l Collect group data and present in a tabular form as given below:

Serial No. Immediate Memory Span Remarks

1 2 3 4 5 6 7 8 9 10 Mean

l Calculate mean immediate memory span for the group for non-sense syllables in the method of paired-associate learning.

Discussion: Discuss what is your subject’s immediate memory span? What is the group mean?

Are there any personal characteristics that influence memory span? Discuss your results with reference to earlier studies.

Ø Reaction Time Experiments

The problem of reaction time was one of the earliest to be studied in experimental psychology.

Helmholtz, Galton, Donders were the first to do experiments on reaction time. The original

experiments were simple and attempted to study the time taken by the person to notice a single stimulus and produce an appropriate response. Later experiments starting with the work of Donders, tried to study reaction time in more complicated situations.

The minimum time between the presentation of a stimulus and the subject’s response to it is known as reaction time. It is one of the oldest dependent variable in experimental psychology. There are various specialized types of reaction time. The minimum lag between a single simple stimulus (e.g. a light or tone) and the subject’s making of a single simple response (e.g. pressing a button or releasing a switch) is known as simple reaction time. Any reaction time when two (or more) stimuli and two (or more) responses are employed is known as complex reaction time. In some situations, there may be several stimuli but a person may have to respond to only one of them, i.e. he has to discriminate one stimulus from the others and respond. This is called discriminatory reaction time. Where a subject has to respond whenever anyone of a number of stimuli occur, but has to make completely different responses depending on the particular stimulus. This involves not only a discrimination of the stimulus but also a choice of a response. This is called choice reaction time. This takes the longest time.