Psych Muller-Lyer Illusion PDF

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Summary

Report on Lab Experiment B-The Müller-Lyer Illusion. The lecturer was Samuel Charlton ...

Description

Introduction The Müller-Lyer Illusion was an experiment conducted by German Psychologist ‘Franz Carl Müller-Lyer’ in 1889. The optical illusion experiment shows how participants can be deceived into perceiving things differently from the same image. The Illusion provided horizontal lines and two types of arrows. The arrows of which being diverging chevrons (arrows pointing away from the lines) and converging chevrons (arrows pointing inwards towards the lines). Although the horizontal lines are all the same in length, the lines with diverging chevrons can be perceived to be longer in length lines with converging chevrons. Thus, this experiment put this theory to test.

The Müller-Lyer Illusion was created to assist psychologists in answering complex questions. Psychologists attempt to explain these illusions by looking more into the brain and perceptual process work. And whether or not our pasts experiences have any effect on our perception of certain things (Department of Psychology, University of Bristol., n.d., para. 3). Furthermore, the main purpose of the experiment is to put the theory to test and to come to a conclusion whether or not the experiment supports the theory made regarding optical illusions.

Previous research on optical illusions included Richard Gregories concept of ‘misapplied size constancy scaling’ this of which applied to the optical illusion in that the the arrowheads engaged the part of the visual system that deals with depth cues in retinal images (Donaldson, D, and Macpherson F, 2017., para. 3). The result of this being that the line with the outward facing arrow was perceived as longer in length than the inward facing arrow because it was being processed as further away (Gregory, 1997).

My hypotheses will be put into practice where all of the students will be completing a version of the experiment carried about by Segall et al (1963). This consisted of the participants adjusting the length of an arrowhead between a horizontal line of converging and diverging chevrons, ‘arrows out’ and ‘arrows in’. Until the point of subjective equality, or where the point that divides is exactly in half.

The experimental hypotheses for the Müller-Lyer Illusion is that as the degrees of the arrowheads (chevrons) increase, the ability to place the third arrow head accurately near the middle of the line decreases as we are most affected by the illusion when the degrees are higher for the arrowheads (eg 60 degrees rather than 0 degrees). The Independent variable for this experiment was the degree that the angle head was angled at (0,15,30,45,or 60 degrees) this is the variable that we manipulated. The Dependent variable is how we measured how each participant placed their third angle head in relation to the centre line (mm) and how far off the central point each participant placed it.

Method

The experiment was done digitally on the application ‘Muller’, where it gave us specific instructions to follow. We were given a series of lines with an arrowhead at each end, where there was an additional (third) angle head in the middle. The angle head in the middle was to be dragged and placed to a point where we believed was central to the line given. Once completed, we would be required to press ‘enter’ or click ‘accept’ to move on to the next line. There were five different possibilities of angle heads that could have been presented (15,30,45, or 60 degrees of angle to vertical), as well as zero degree arrowheads (vertical lines). Each line was presented 12 times throughout the experiment, in random order. Thus there was a total of 60 trials/lines given throughout the experiment.

Results

Estimates Measure: MEASURE_1 95% Confidence Interval arrowhead

Mean

Std. Error

Lower Bound

Upper Bound

1

.069

.151

-.230

.369

2

5.827

.393

5.046

6.609

3

10.543

.485

9.579

11.507

4

13.683

.468

12.752

14.614

5

17.832

.524

16.790

18.874

The results from the experiment shown in the graph above supports my hypothesis because as the degrees of the arrowheads increase the accuracy of placing the third arrowhead central decreased. Thus, this shows that the illusion had on effect on our ability to perceive the central point accurately. The graph displays an exponential increase in the mean distance from the centre (mm). At zero degrees the mean distance from centre was 0.069mm, this made sense because when the degrees are lower (at zero degrees) as a participant I found it was much easier to place the third arrowhead near the central point of the line. At 15 degrees the ability of locating the central point became more complex and the accuracy was decreasing. This was shown with the mean increasing significantly to 5.827mm, thus it increased by 5.758mm from zero to fifteen degrees. The same pattern was seen at 30 degrees where the mean distance from the centre was not far off doubling at 10.543mm, increasing by 4.716mm. Again at 45 degrees the mean increased less than previously, but nonetheless still increased to 13.683mm, (an increase of 3.14mm). And finally at 60 degrees at the highest the mean distance from centre at 17.832mm. Overall, the results match up with the hypothesis and clearly support the theory that as the

degrees of the angle heads increase the ability to place the third arrowhead near the centre of the line decreases.

Discussion Overall the results of the experiment matched up with the previous research carried out by Richard Gregory with the concept of ‘misapplied size constancy scaling’, both of which concluding that as the degrees of the arrowheads increase, the ability of a participant to accurately place the third arrowhead in the middle of the line decreases. Thus, this indicates that the experiment was successful as we drew the same conclusions as Gregory did back when he was applying these theories to a practical setting. (Gregory, 1997).

There are a number of limitations of the experiment that may have affected the validity and reliability. There was the potential for distraction throughout the experiment as we were in a classroom full of participants completing it simultaneously. Furthermore, the rate at which the experiment could be completed at was dependent on how fast each participant placed each third angle head to each line. Thus, there was the potential for students rushing each of the trials and getting inaccurate results. There was also a minor source of bias in the experiment where we knew the expected result before we begun the experiment, therefore this could have assisted participants in some way or another participants, thus creating a source of bias. Because as participants, we knew what we needed to get for results therefore it was just a matter of physically gaining the results. As reinforced by the experiment description provided it stated “do not try to overcompensate to get a perfect answer now that you know what the answer is”. Another potential limitation was the number of trials and they could have been increased to gain a better representation of each participants ability, thus being a better representation of the overall experiment. Finally, the vision of participants was not checked therefore certain participants could have better vision in comparison to others. This created a source of bias as participants could have an advantage over other participants. If the vision was to be checked this would not only clear any bias but it would in turn better represent each participants true ability of the experiment.

References

Gregory R.L. (1966). Eye and Brain. New York: McGraw-Hill

Department of Psychology, University of Bristol, 8 Woodland. (n.d). Knowledge in perception and Illusion. Retrieved from Department of Psychology, University of Bristol http://www.richardgregory.org/papers/knowl_illusion/knowledge-in-perception.pdf

Donaldson, D. and Macpherson F. (2017). The Illusions Index. Retrieved from https://www.illusionsindex.org/ir/mueller-lyer...