Muller-Lyer Illusion Essays Examples

The Muller-Lyer illusion is a useful tool for investigating the effects of the environment on human perception. The illusion shows that humans use the surroundings of an object to make a judgment of the size of that object, which is not necessarily accurate. The theory of size constancy suggests that we can usually make a judgment about the size of an object based on depth perception, the nearby objects, what we already know, and other factors. The Muller-Lyer illusion is an example of that system being tricked due to the presence of an acute or obtuse angle. It is size constancy that causes the lines to appear distorted and differing in length, despite the fact that they are not. Experiments on the Muller-Lyer illusion show that people consistently make the judgment that the line with the obtuse angles is longer than the one with the acute angles.
In this experiment, the Muller-Lyer illusion was used to gather data about perception. As expected, the individuals in this study consistently estimated the line with obtuse angles to be longer than the one with acute angles. In the first experiment, the estimated length for the acute condition was 5.485 compared to 6.1975 in the obtuse condition. The second experiment showed 5.555 for the acute condition compared with 6.3425 in the obtuse condition. This provides evidence that it is size constancy that is causing the effect, rather than shape constancy, as there shape constancy allows us to see an object as being the same shape even when the perception is different. If shape constancy was playing a role, it is likely that the participants would perceive the lines as being the same shape and therefore have no difficulty making an accurate judgment about the length of those lines.
The theory of shape consistency is used to explain why we can see a door, for example, from several different angles but still perceive it to be a rectangle. The perception of distance and the environment is, again, the major factor in allowing us to make this assessment. In the case of this experiment, it could be argued that participants perceive the line to be two different shapes because of the angles that are flanking it. Despite this, the more likely argument stems from the fact that we are used to using diagonal lines as depth cues. In a normal perspective drawing, the lines diagonally face inwards, due to the fact that objects that are further away appear smaller. Our brains take this information and allow us to perceive the object as being the same size all across. In the acute angle scenario, the lines are pointing inwards in a similar way, which causes our brain to process it as being further away and thus smaller.
The theory of size constancy would also support the idea that the participants would see the lines as the same length as the shapes themselves (the angles) are the same, just put into different perspectives. If size constancy applied here, then it would be likely that the brain would be able to process the fact that these two shapes are the same and the line would appear the same. The argument that the angles represent depth of vision similar to what is shown in a perspective drawing is more convincing as it gives a real example of how we perceive things based on the visual cues around them. As such, it seems likely that the major player in this is the concept of size constancy rather than shape constancy, based on the arguments outlined above.