An experiment was carried out with an opportunity sample of sixth form college students as participants. The aim was to study the effects of prompts on people’s perception of visual illusions (perceptual set). The participants were each shown 10 visual illusions, which could be seen in two ways, and asked if they could see both forms or not. The prompt was given in the question the participants were asked. The experiment tests people’s perception (and comes under cognitive psychology). The Mann-Whitney U test showed the results to be significant at the p=0.05 level, which means that the experimental hypothesis was accepted which states that the results would favour the prompted condition.
Perception and perceptual set are areas studied by cognitive psychologists. Our ability to perceive is often based on expectations, if people expect to see more than one form of an image; they may be more likely to do so than if they have no expectation, this is due to perceptual set. Perceptual set is a non-intentional mental predisposition that influences how we perceive visual and non-visual information. When a person is given only partial data their brain fills in what it expects the missing information to be.With visual illusions, there is more than one way to view the same image, and our vision will flicker between them, provided that we are able to see both forms of the image. Bugelski and Alampay (1961) did an experiment in which they showed people an image which could either be perceived as a rat or as an old man wearing glasses. Before the participants where shown this image, they were shown either images of human faces or images of animals:
Since the participants were either expecting to see another face or another animal, their perception was changed, and consequently 100% of the animal group saw a rat in the last image and between 73-80% of the faces group saw a face of an old man with spectacles. There was also a control group, which was not shown any images beforehand, and 81% of this group said that they saw the image as that of a man rather than a rat.
Based on expectations affecting our perception of visual illusions, it was expected that people given prompts would be more likely to see both forms of the visual illusions, and so the hypothesis was developed around this. The rationale of this experiment was to see if perceptual set exists amongst students.
Research hypothesis: There will be a significant difference in the number of illusory figures seen by a group if participants given prompts than those not when presented with ambiguous figures.
Null hypothesis: There will be no significant difference in the results of the two conditions.
The experimental method for this study is a laboratory experiment; this method was chosen as control over extraneous variables was necessary. This method suffers from demand characteristics, but this was overcome by a control. The experimental design of this study was independent measures. The advantages of this design are that the same test can be used (which is essential for this study), and it reduces order effects. The independent variable of this experiment was whether a prompt was given to the participant in the question or not, the dependant variable was the score out of ten that the participants achieve.
The study used an opportunity sample, in which the population was made up of students, and the sampling frame was students from a sixth form college aged between 16 and 18. Altogether, forty participants were tested in this study, twenty randomly assigned to each condition by tossing a coin to avoid order effects.
The images that were shown to the participants were all images which could be seen in two forms, so that they could say whether they could see both forms of the image or not and be scored accordingly. There were ten images in total; shown one after another to the participants (see script in appendix). When the participants were being shown the images they were asked either “How many things do you see?” if in the prompt condition, and otherwise “What do you see?” if in the non-prompt condition. Each participant was tested individually and shown all ten images. This is a standardised procedure which can easily be replicated.
If participants said that they could see both forms of the image, they were asked to outline both forms of the image, in order to ensure that they could actually see both forms of the image and that they were not lying due to demand characteristics.
The participants gave consent, but were not told the aim of the experiment, this was necessary to reduce demand characteristics. There was no personal data gathered, participants had the right to withdraw at any time, the participants did not suffer any harm, and at the end of the experiment all participants were debriefed.
Measurement and analysis of data
The participants were given a score of either 1 if they could see both forms of the image or 0 if they couldn’t for each image. After each test on a participant, they were given a score out of ten for all of the images. These scores were used in the statistical tests.