So how does this process work? Let’s start with the stimulus. Pretend you’re in the market. It’s seven in the morning, and you can feel the sun bearing down on your neck. The air is hot and sticky on your skin. It’s crowded and noisy, and all around you people are haggling over fruits and vegetables, while over everything hangs the distinct smell of a fisherman’s freshly-caught haul...
All of the sensations bombarding you – the hypothetical you in the marketplace – is considered a stimulus. Specifically, these are called environmental stimuli. Environmental stimuli surround us every day, but we don’t often notice them until they become attended stimuli. A stimulus becomes attended when you focus your attention on it – for example, can you find the pear in this picture?
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Eventually your attention will wander elsewhere, and the attended stimulus will change, but until then, your brain will be busy creating an image or representation of the pear in your eyes – this is called the stimulus on the receptors.
As your receptors receive energy from the environment, it undergoes a process called transduction in the nervous system, which transforms the energy from the environment to electrical energy. The pattern of light created in your retina when you saw the pear will be transformed into electrical signals which will activate neurons which in turn will activate MORE neurons. Eventually, these signals will reach the brain where it will be processed. One thing we must always remember is that although the signal that reaches the brain is a representation of the original stimulus, it is different from the original signal.
All of these will then transform into something we are aware of-- perception. Perception is a conscious sensory experience which results in recognition and action-- two important outcomes of the perceptual process. Recognition is our ability to place an object in a category that gives it meaning while action involves motor activities and moving through the environment (which would translate to our behavior in response to our perception of the stimulus).
Let’s go back to the market. Assume that you did see the pear. Once your brain receives the signal from the receptors in your eyes, you will be aware that what you’re seeing is a lone pear in a basket full of apples. Not only did you categorize the pear as being a pear, you also categorized it as not being an apple. Seeing as the pear does not belong in that basket, you pick it up, and you place it in its rightful place-- the basket with all the other pears. That is your action.
Your knowledge, whether learned years ago or recently obtained affects perception as well. The fact that you know what a pear is and how it looks like is an example of how knowledge learned years ago affects perception. There are 2 different ways of processing information and these are bottom-up processing and top-down processing. In bottom-down processing, processing is based on incoming data. For example, the incoming data would be the light on your retina coming from the pear and the apple. Then, that is when you perceive it to be an apple or a pear. Top-down processing, on the other hand, is processing based on knowledge. Since you have previous knowledge that apples are green and round, you perceive the things you see as apples.
As we’ve seen, the perceptual process is complicated and it happens faster than a blink of an eye. As you’re reading this, the perceptual process has probably gone through the motions a hundred times already. There are a lot more things to learn about perception and what we’ve discussed above is just the tip of the iceberg-- an overview of something bigger.
References:
Goldstein, E. B. (2010). Sensation and perception (8th ed). Belmont, CA: Cengage Learning.
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