Perception

“Perception is the process by which we recognise what is represented by the information provided by our sense organs” (Sarma, 2010). As well as our ability to perceive the shape of the objects, we are also able to judge its location and its movements. Perceiving the location of things and their movements are all important roles of the visual system (Decety et al., 1997; Jeannerod, 1997 in Sarma, 2010). Depth perception requires that we measure the distance between us and the objects in the environment .Our ability to do this is aided by two types of cues: binocular (two-eyes) and monocular (one-eye) (Sarma, 2009). With binocular cues the eyes make conjugate movements so that they converge at the same point on the object (Sarma, 2009). Binocular vision is the part of the vision system which uses two eyes (Entzinger, 2009). It is the opposite of monocular vision, in which only one eye is, utilized (Entzinger, 2009). Convergence plays an important role for perceiving the distance of objects especially the distance of objects that are near hand to us (Sarma, 2009). Our eyes will be turned slightly inward when an object is in close proximity to our face, however when an object is further away our eyes tend to look straight ahead (Sarma, 2009). Retinal disparity and stereopsis also play other important roles in the perception of distance. Stereopsis is concerned with the perception of depth based on horizontal binocular parallax, which is a change in the way of viewing because of the existence of horizontally separated eyes (Wheatstone, 1938 as in Patterson, 2009). Binocular disparity evolves from binocular parallax, which is a change in the position of similar images that stimulate the two retinas (Patterson, 2009). Binocular cues have many benefits and one of which can be seen in the landing of aircrafts. Depth and distance perception are all important factors when landing a plane. “Stereopsis is considered an important depth cue especially for close range operations such as landing, formation flying, aerial refuelling, helicopter operations and ground operations” (Entzinger, 2009). In Monocular cues one of the most valuable sources of information in regards to the distance of objects is interposition (Sarma, 2010). Interposition basically refers to the fact that if you are looking at one object in the distance and another object was placed in between you and the first object, that you would automatically know which of the objects was closer to you (Sarma, 2010). In regards to the question at hand our familiarity with the size of objects is an important monocular distance cue. Let’s take a tractor for example. If a tractor casts a small image on our retinas, we will perceive it as being far away (Sarma, 2010). However with our knowledge of how big tractors are our visual system will automatically compute the distance from the size of the retinal image (Sarma, 2010). An important characteristic of the visual system is that it is always changing due to our movements, objects movements and due to the change in the lightening conditions. Even with all of this however, our perception of images still hugely remains the same. The two main constancies which revolve around this are form and brightness. With the brightness constancy, people can usually tell how white or grey an object is even when the level of brightness changes (Sarma, 2010). You will perceive a white sheet of paper as being white either in excellent lightening condition or even in poor lightening conditions (Sarma, 2010).You will also perceive a grey piece of paper as being grey in sunlight , even though it may reflect more sunlight onto your retina than a white piece of paper in the shade (Sarma, 2010). From constancy refers to the fact that as we approach an object we do not perceive it as becoming bigger (Sarma, 2010). Even though the image might be become larger on our retinas, we do not actually perceive it as becoming larger (Sarma, 2010). We perceive this change as a decrease in the distance between us and the object in question (Sarma, 2010). Our perception of the size of objects remains the same or relatively constant (Sarma, 2010). Psychologists sometimes refer to this as size constancy or height constancy, but size and height constancy only refers to certain aspects of form (Sarma, 2010). Before the twentieth centaury Hermann von Helmholtz suggested that form constancy was achieved by unconscious inference (Sarma, 2010). This is a mental computation of which we are unaware (Sarma, 2010). We already are aware of the size and shapes of familiar objects, therefore if an object appears small on our retinas we perceive it as being far away, while if an object appears large on out retinas we perceive it as being close to us (Sarma, 2010). Either way, we will always perceive the object itself as being the same size (Sarma, 2010). In conclusion it is evident from the above the importance perception plays in the field of our vision. It also highlights the importance of binocular cues and monocular cues, and how these can be associated with depth perception. Even though our visual system is constantly changing our perception of images still hugely remains the same and this is due to the various constancies which have also been outlined above. Reference List Entzinger, J.O. (2009). The role of Binocular Cues in Human Pilot Landing Control. Thirteenth Australian International Aerospace Congress. 13 (1), p1-15. Patterson, R. (2009). Human factors of stereo displays: An update. Society for Information Display. 17 (12), p987-996. Sarma, K (2010). Introduction to Psychology. 4th Ed. Great Britain: Pearson Education Limited. 258-266.