ABSTRACT

The purpose of this experiment is to test for interference in visual perception.

The stroop test is an effective way of measuring the difference between visual perception with interference and visual perception without interference.

For the purpose of this experiment a two-tailed hypothesis was chosen.

Hypothesis (H1), ‘ that there will be a significant difference in the participants information processing time under two different conditions of the stroop effect, Condition A and Condition B’, the Null Hypothesis (H2) proposed that there would be no significant difference in the participants information processing time under two different conditions of the stroop effect, Condition A and Condition B’.

A random sample of a homogenous population was used for the experiment. Statistical tests which were applied were ‘t’ test and Spearman’s Rho. The level of significance was 0.05, this means that there is a one in twenty chance that what occurred in the stroop experiment occurred by chance factors and allows for (n-1) degree of freedom ie a 19/20 chance that the IV affected the DV. The critical value used is 2.861.

The experiment discovered that there was a significant difference in the participants processing times for Condition A and Condition B, thereby proving H1, ‘that there will be a significant difference in the participants information processing time under two different conditions of the stroop effect, Condition A and Condition B’. Thus showing that interference in information processing does occur under different conditions.

INTRODUCTION

It is the cognitive School of Psychology which is involved in exploring and investigating the way the mind processes and stores information.
Cognition can be divided into groups which include but are not confined to attention, language, thought processes, memory, perception and problem-solving.

A cognitive psychologist will explore these hypothetical constructs by carrying out experiments which require the participants to use memory or problem solving skills.

Automatisation is a process whereby tasks which are regularly or frequently performed become almost automatic so that they require very little active memory or problem solving in order to be performed, e.g. reading, the physical process of driving, riding a bicycle, recognising colours and sounds are functions, which make use of the process of automatisation. It is when interference occurrs in this process that the individual becomes aware of some of the functions their brain is performing. Our brains experience a constant bombardment of sensory information and stimulation from our sense organs. The brain then has to sort out the important sensory information from the not so important information, to make the process easier the brain uses automatisation so that some tasks can be completed using very little of the sensory information required to complete other tasks. The processing and organising of incomming sensory information is known to psychologists as perception. Perception is each individual brains interpretation of external stimuli, we can not be 100% sure that everybody percieves the world around them in exactly the same way and therefore we can assume that in part, at least, perception is unique to each individual.

The Stroop effect (Stroop 1935), is an effective way of showing how interference can occur in the process of automatisation. The Stroop effect shows how the brain can become confused by a combination of words and colours and slows down the information processing time. In cognitive psychology the information processing procedure is often compared to the processes used by a computer.

The Stroop effect phenomenon can be shown in the experiment known as the Stroop colour-word test. This experiment deomonstrates how responses and automatic processing are subject to interference.
It is expected that this experiment will show that some tasks which are normally processed by the brain automatically take longer to complete and require a greater amount of attention when interference occurs.

Previous studies which have explored interference have been carried out by many psychologists, Kahneman (1973) put forward the idea that human beings have only a limited amount of processing capability and the information processed by the brain is dependant upon how much processing is taking place at one time, therefore if the processor was being used to near mazimum prcessign capability there is litle room for other information and this information is therefore unprocessed and is left out (Gross, fourth edition, 2001, p191).
Later Norman & Brobrow (1975) put forward the idea that there are two distinctly different processes by which information is dealt with in the brain, the process used being entirley dependant upon the type of information to be processed. The processes are called data limited processing and resource limited processing. The quality and speed of the processing is defined by the external influences at the time of processing, therefore, external stimuli can ‘interfere’ with the processing capabilities of the brain ( Gross, Fourth Edition, 2001, P192). Broadbent (1982) showed that when two tasks are performed at the same time interference does occur because there is some disruption in the speed and efficiency of how the brain copes with more than one task. (Gross, Fourth Edition, 2001, p192).
It was Schneider and Shiffrin (1977), who carried out studies into processing and labelled two forms of processinexplanation further andg as Automatic Processing, that which makes virtually no demand on attention and Controlled Processing, that which makes large demands on attention, i.e. tasks which require concentration to perform. (Gross, Fourth Edition, 2001, p193).
The stroop effect demonstrates these two types of processing and how they cause confusion when they are in action together competing for priority in processing, this is known as interference.

METHOD

This experiment was undertaken using the repeated measure design, which is when all of the participants in an experiment experience all conditions. This serves the purpose of allowing the participants themselves to act as the control for the experiment. All of the participants in this experiment experienced both Condition A – 3 lists of neutral words printed in coloured ink, and Condition B – 3 lists of Colour words printed in coloured ink. To avoid learned behaviour affecting the results of the experiment, the group of participants were divided into two sections, the first 10 participants were given lists 1, 2 & 3 first followed by lists 4, 5 & 6. The second 10 participants were given Lists 4,5 & 6 initially followed by Lists 1,2 & 3.

The participants were approached individually and asked if they would like to take part in an experiment, which was examining perception. The Participants were chosen at random, from the Students who attend James Watt College, North Ayrshire Campus.
The experiment took place in a small room adjacent to the library and the Participants were tested one at a time.
The Participants were all given the same 2 pieces of paper to read, which would act as a simple test for colour blindness and dyslexia. The first sheet was an explanation of what was required of the participant for the purpose of the experiment, the second piece of paper contained four boxes each coloured in a different primary colour red, yellow, blue and green. This also assured the experimenters that each pariticpant was of a simillar standard of intellectual ability. The participants were reassured that this was not a test of intelligence or intellectual abilities and that there were no right or wrong answers. Once the experimenters were satisfied that the participant could distinguish the primary colours and the participant was at ease, the participant was asked if he/she was ready and the experiment began.

In the room were 3 students carrying out the experiment, 1 to record the times for each list on a chart, another to record the mistakes made for each list on a separate chart and one with a stop watch to time the participant for each list.

Materials:
Chart to record time Three lists of Neutral words
Chart to record Mistakes Three lists of colour words
Stop watch Test card of primary colours
Pens Passage for participants to read
Procedure:

Participants were given times to come to the room adjacent to the library, they were met by a member of the experiment team and introduced to the other members of the team to put them at ease. They were then asked to sit down at a table and were asked to read a short passage and a test card containing four coloured rectangles one of each , red , blue, green and yellow. The participant was then asked if they understod what was required of them and it was reittereated that it was the colour of ink that was required to be named not the written word. Once it was established that the participant felt at ease and understood what was requied of them he/she was asked to indicate when he/she was ready. The participant was then given each list one at a time. The times were recorded by a member of the experiment team using a stop watch and written down on the time chart, any mistakes were recorded by another member of the team on a mistake chart. When the participant was finished reading all six lists tey were thanked for participating and reassured that the experiment was not of intelligence or intellectual abilities. The participants were told the true nature of the experiment and thanked for participating.

RESULTS

The raw data from Condition A and Condition B was then totalled and the figures rounded up or down to form whole numbers. The mean and mode were then calculated for each participant and the mean and median for each list in condition A was calculated and then the mean and median for each list in Condition B was calculated. The standard deviations for each condition were also calculated.

Stroop Effect:

Condition A Condition B
(Neutral words) (colour words)
Mean = 11 Mean = 14
Mode = 10 Mode = 11

Total mean for Total Mean for
Condition A Condition B
216.67 284.65

Standard Deviation Condition A = 5.10

Standard Deviation Condition B = 7.63

Condition A shows a significantly lower result than Condition B.

TREATMENT OF RESULTS

Spearman’s Rho was used to provide inferential statistics and descriptive statistics were used to form Graphs to illustrate the results. Because the experiment used a two-tailed hypothesis and because the experiment itself was of a parametric design i.e. the participants were drawn from a normal population distribution and the data tested is continuous a ‘t’ test was performed. This test would show whether the Hypothesis was to be rejected or proven.

The ‘t’ test result is as follows;

Condition A Condition B
Participants =20 Participants =20
Total mean result=216.67 Total mean result =284.67

Degree of freedom = 19 Critical value of ‘t’ = 2.861
Significant level of ‘t’ = 0.05 (because this is a two-tailed hypothesis)
The mean difference between Condition A and Condition B = 3.4
‘t’ = 6.64

Spearman’s Rho result for this experiment Rho = 0.99 (see appendix )
Size of n = 20 level of significance = 0.05

Spearman’s Rho test was used to analyse the data because this experiment used a two-tailed hypothesis, with a sample size of 20. The relationship between the IV (participant times) and the DV (Stroop effect) were examined to see if one variable could be attributed to the difference in the other variable this is what Psychologists term correlation. Spearman’s Rho is used to assess the correlation between the variables in the experiment. The strength of correlation is determined by the number of ‘r’ this can vary between 1.00 and –1.00.

Discussion:

This experiment shows that it takes longer for the brain to distinguish colours when a colour name is written in a different coloured ink, than it does to distinguish colours when a neutral word is written in coloured ink. It appears to be that some confusion occurs in the processing methods of the brain, which slows reaction times, thus showing that some perceptual interference is occurring.
H1 ‘that there will be a significant difference in the participants information processing time under two different conditions of the stroop effect, Condition A and Condition B’ can therefore be accepted and H2 ‘that there would be no significant difference in the participants information processing time under two different conditions of the stroop effect, Condition A and Condition B’ can be rejected.

If this experiment were to be repeated it would be interesting to see if a stimulant such as caffeine or a depressant such as alcohol would have any effect on the results. This experiment took place in May when a lot of the participants may have been under stress because of examinations and the workload at the end of the academic year. It also took place at lunchtime when students may have been concerned over how long the experiment would take because they hadn’t had their lunch or were perhaps sluggish because they had just eaten. However students at James Watt College provided a varied age range within it’s population.

This experiment supports previous ‘stroop effect’ experiments and other experiments, which test for interference, Cherry for example tested for interference in the processing of sound by asking participants to listen to different sounds in each ear, one sound was ‘shadowed’ by the participants, they were then asked to relate back what they had heard, the participants had much greater recall of the sounds which were not shadowed and had difficulty in remembering the shadowed sounds, (Gross, Fourth Edition, 2001, p196).

Flowers et al (1979) used numbers to demonstrate the stroop effect,
They found that people had difficulty in saying how many numbers were in a row and were more likely to read the actual written numbers as follows.

555
1111
2
33333
44
555
44444
5555
3
444
222
33
444
111
3
222

This version of the Stroop effect also demonstrates that interference occurs in visual processing because the learned action of reading dominates the process of counting (Gross, Fourth edition, 2001, p194).
CONCLUSION

The purpose of this experiment was to show that interference in perceptual processing can occur and that some cognitive processes require a greater amount of attention than others. The experiment also showed that there is an element of fallibility in automatisation.

To test this theory of cognition it was decided that the Stroop Colour-Word test be used.

This test Validated H1, ’that there will be a significant difference in the information processing time under two different conditions of the Stroop effect, Condition A and Condition B’ and rejected the Null Hypothesis H2,’ that there will not be a significant difference in the information processing time under two different conditions of the stroop effect, Condition A and Condition B’

Thus it can be concluded that for the sample used the Stroop Effect Theory has been validated.(S.McGonigal)