Introduction
Sensation is the process of collecting all information from the outside world and sending it to the brain using the nervous system. It is described as a passive process since one does not need to consciously take time to sense. On the other hand, “perception is the process of actively selecting, arranging and interpreting the information rendered to the brain through the sensory system” (Gibson, 1986).
Thus the process of perception occurs in two main stages or processes. The first process that occurs is sensation. The sensory system is composed of the sensory organs nose, eye, tongue and the skin and the nervous system that transfers the information in form of impulses to the brain. The next step is the process of organizing the received stimuli so as to make a meaningful idea of the situation. A selection or discrimination of the received information is done to define what is meaningful and important to the body. Motivation is used to consider what is important to the body and thus pays selective attention to the stimuli. For example, “students in a class will pay attention to the teacher disregarding noise coming from outside because they are motivated by learning” (Goldstein 2009). Thus it is clear that perception is more than just sensation. Many scholars have argued this out in the perception theories.
One of the theories put forward is the Top-down Processing theory of visual perception. In this theory, Gregory (2009), argues that “perception of a visual stimulus is a process that requires building on past images so as to make out the final image.” The theory suggests that the information that reaches our brain from the eye is, in most cases, distorted or lost. Therefore the brain refers to some past experience so that we can actively construct the image.
Research and experiments in the top-down theory have been extensively done. This has proved that perception can be ambiguous since the brain can develop two hypotheses and is incapable of deciding between them. A good example is the Necker cube. It has been proved that staring at the crosses of the cube will flip the orientation of the cube. Therefore one pattern or image will have produced two different perceptions that the brain is not able to discern. The second research that has been done on the top-down theory of perception explains why unlikely objects are sometimes deemed to be what they are not. In the research, a mask of a nonexistent object or being is made. In this experiment, there was an overpowering need to liken the mask to something familiar like a dragon in a comic or a story.
The second theory that has been suggested is the Bottom-Up or Direct Theory Processing of visual perception. The theory directly contradicts top-down theory by asserting that the information received from the environment is enough to perceive without reference to any past experience. According to this theory, perception is the sensation that what we see is what it is and that no further interpretation is needed. This means that “received information from the sensory system is analysed from simple specifics to complex conclusions” (Gibson 1986).
An example for this argument is the straight motion parallax. In this illustration, as we move in a car or in a train, the motion of objects closer to the car move faster than those far from the car. This is true simply due to the relative distance between the objects and the car.
In the research of this theory, it was proved that optic flow patterns that pilots experience give them true information about the position, speed and direction at which they are flying. The demonstration suggests that if there is any flow in the optic range, then the perceiver is in motion. The center of the flow is the point that indicates the direction of motion of the perceiver. If the optical flow is seen to be coming out of this center, the perceiver is moving towards the point and vice-versa.
Other experiments that prove this theory is the superimposition theory that suggest that an object that blocks another is perceived to be closer. Another fact is that an object appears smaller when it is further away than when it is near.
This theory has however come under criticism. The direct theory has failed to explain the perception of illusions or nonexistent objects. For example, the theory cannot explain why vertical distances are generally overestimated compared to the horizontal distances.
Neither the Top-down nor the Bottom-up theories of visual perception is adequate to make a complete and accurate perception of the situation at all times. The bottom-up theory is based on the perceiver enjoying enough time to view the object and is reliant on the clarity of the object. While the top-down theory relies on a lot interpretations and experience. Scholars have suggested that the use of past experience combined with the clarity of the stimuli input will go along way in perceiving our environment. Perfect perception has to go beyond sensation and stimuli clarity.
References
Coren, S., Ward, L., & Enns, J. (1999). Sensation and perception. London: John Wiley & Sons, Incorporated.
Gibson, J. J. (1986). The ecological approach to visual perception: Resources for ecological psychology. Chicago: Routledge.
Goldstein, B. (2009). Sensation and perception. New York: Cengage Learning.
Gregory, R. L. (1996). Sensation and perception;Longman essential psychology. London: Longman.
May, M. (2007). Sensation and Perception. New York: Infobase Publishing.
Wolfe, J. (2009). Sensation and perception. Boston: Sinauer Associates, Inc.
