The Importance of Size Constancy and Size Perception - Essay Example

?The Importance of size constancy and size perception. There has been considerable research in the past, to examine the way that perception of the size of an object actually works. It was thought previously that the size of an object and the distance of an object were perceived using similar processes in the brain. This explains why so much of the research on size perception and distance perception considers both of these concepts in joint studies. They were seen as being inextricably linked and so were examined using similar methods and experiments. The work of Haber and Levin (2001) re-examined this whole area and discovered that in fact the two dimensions of size perception and distance perception are not so similar after all, and that new methods are needed to tease out the differences between them. Haber and Levin (2001) noted that the bulk of past research had focused on perception of distance and that perception of size had received comparatively little attention. This is justified to some extent because the perception of distances, and of both moving and static objects within that space, is a process that humans need to become familiar with at a very early age, since this is necessary for humans to be able to move about in the environment. Perception of distances has to be very quick, and automatic, because it is needed all the time, in familiar and unfamiliar locations. Perception of size, on the other hand does not need to be checked constantly in the way that distance does, because once an object is recognized, a host of properties are accessed. This, or another similar object, has been experienced before, and the perceiver just remembers all of this information without having to perceive it anew every single time. This difference between perceiving distance, a task that that changes all the time depending on the location and the amount of movement in the person and the object in the environment, to perceiving size, which is much more fixed according to object type, is therefore very important. In effect this means that the perception of an object is not so much a process of perception but rather it is a cognitive process that depends on memory of past experience. Haber and Levin (2001) set up an experiment to test how big a role memory plays in perception of size. They realized that familiarity with an object was a key factor in its perception and so they devised categories for measuring this, including prototypic size which applies to all similar versions of an object. Assessing participants’ estimation of objects which were in view, and those which were not, data can be gathered that sheds light on the difference between seeing an object, and just thinking about it from memory. College students are able to estimate the size of common objects quite easily and accurately even when the objects are not visible. When they view objects which are unfamiliar to them, accuracy falls, suggesting that people rely more on memory of an object they are already familiar with, or of similar objects they have encountered in the past , than on perception of an actual object in the present. When there is a possible range of sizes for a particular object, which is called token variability, this also reduces accuracy, suggesting that both perception and cognition play a role. Distance was the most important factor in determining size, familiarity, and the variability in possible size of an object all played a role. Cognitive processes were used when distance information was poor. This suggests that distance is not the most important factor in estimating the size of unfamiliar objects. The researchers conclude that “our knowledge of the world and not our perception of the world determines our estimates of size in the world” (Haber and Levin, 2001, p. 1151). This creates a whole new area of research because it is still not clear exactly how size perception works. Later work by Wesp et al. (2004) on this problem of determining how size estimation is carried out set up an experiment to evaluate how well observers estimate the size of an object when it viewed in use. In the examples chosen (taking sand out of a ladle with a small spoon and a large spoon, for example), observers consistently over-estimated the size of the ladle when the process was long and laborious, with the smaller spoon, which suggests that perception is affected by other factors such as the observer’s understanding of the action that is taking place involving the observed object. This means that observers interpret the size using deductions about the action. The way that objects are used appears then also to be a part of the process that we use to perceive them: the size estimates that we hold in memory can be changed by experiences using an object, and by observed manipulation of an object. Something to do with the complexity of the viewing experiences brings in more elements of cognition, it appears, and this can distort size estimation by perception. The problem is addressed from yet another angle by Kaufman et al. (2006) who look more closely at perceived distance and actual distance, though they prefer the term “perceptual distance” because of past confusion in the use of the term “perceived distance”. They tested how far the cue of binocular disparity affects depth and size perception and concluded that it affected both estimations in a consistent way and that “distance is processed prior to angular size” (Kaufman et al., 2006, p. 455). Overall, therefore, it is becoming clear that size perception is indeed linked with distance perception, but these two processes are different, both in the order in which they are employed, and in the degree of cognitive processing that they entail. If similar experiments were to take place today, it is likely that experimenters would design them in such a way as to test static objects, familiar object, including some that exist only in one typical size, and some that can vary, and they would also test what happens when the objects are moved, and when they are actually manipulated in some kind of meaningful context. Only by looking at all these variables will it be possible to investigate fully the way that size is estimated. References Haber, R.H. and Levin, C.A. (2001) The independence of size perception and distance perception. Perception and Psychophysics 63(7), 1140-1152. Kaufman, L., Kaufman, J.H., Noble, R., Edlund, S., Bai, S. and King, T. (2006) Perceptual distance and the constancy of size and stereoscopic depth. Spatial Vision 19(5), 439-457. Wesp, R., Cichello, P., Gracia, E.B. and Davis, K. (2004) Observing and engaging in purposeful actions with objects influences estimates of their size. Perception & Psychophysics 66(8), 1261-1267. Read More