Perception

Why would someone study perception? What does studying perception mean? Perception is a conscious sensory experience. It happens when an electrical signal is sent from a stimulus, and those signals are turned into an idea of something, compared with the knowledge we already have. Take for instance the cafe I am in. Everything that I see when I look outward is the “environmental stimulus” – everything I can see has the possibility of being taken in more closely. I decide to focus my attention on my cup of coffee. This is called the attended stimulus. It is similar to when you look through your viewfinder in your camera and then focus on one part of the image.

When I look at my cup of coffee, light reflects on the back of my eye (the retina) and a representation of what the coffee is and looks like is sent to my brain. This is when the actual act of what we often think of “perception” occurs. Our brain will take our experience with the item into account. We already know this is coffee. We might also know that it tastes good. That it is not tea. That it is not cola. That it is warm. We may also take an action. I picked up my coffee and drank some of it.

The process of sending the representation of what we see to the brain is the most technical part of the process. First there is transduction. The energy from the light on the retina activates neurons that are sent to the brain and activate more neurons and soon this information is processed. What the retina “saw” the brain now “sees”. The foreknowledge that we come with that helps this processing is called “top down processing. It takes into account our experiences. Bottom up processing is whatever we are taking in at the moment. The image that is processed on the retina by the light.

It is helpful to study perception because we become more aware of how our mind works, how sight works, and how what we see may only be an idea of what is truly in front of us.

There are two different ways to study perception. The first is psychophysical. This came about in 1860 when Gusav Fechner wrote Elements of Psychophysics. He wrote about measuring the relationship between the psycho (perception) and physics (stimuli) in a quantitative method. The physiological approach measures the relationship between stimuli and the physiological process.

When you say “studying perception” it implies that there are ways to measure what one perceives. This is done in several different ways. Describing, recognizing, detecting, perceiving magnitude and searching.

If someone asks you “what did you perceive?” this is the phenomenological method. This is the most general, and first step, because it describes what we saw and when we saw it. What does something taste like? What color is it? How far away is it? This gives us a basic idea of what someone has perceived.

When we recognize an object and name it, for example “red” or “far” we are continuing to use the phenomenological method.

We detect a perception by using quantitative methods. Limits, adjustment, and constant stimuli. These are described in Gustav Fechners book Elements of Psychophysics. These methods are called the classical psychophysical methods. They were the original methods used to measure stimulus/perception relationship. To be able to detect a stimulus it must be of a certain level. This level is called the absolute threshold. For instance, the smallest flash of light that would be detectable would be an absolute threshold. To determine this you may turn the music on the radio up very slowly until someone is able to hear it. This would be a method of limits. It is done in steps. The method of adjustment is done continuously until the observer can barely detect a stimulus. The method of constant stimuli is presented in different intensities in a random order to see which are detectable.

The difference threshold is the smallest difference between two stimuli that a person can detect. The easiest example to use is weight. It is much easier to tell the difference between a 25lb bag of rice and a 1lb bag of rice than it is to tell the difference between a 25 and 24 bag of rice.

Another method of measuring perception would be the ‘search’ – an example be looking for your friends face in a crowd. While we are fairly sensitive to faces (faces being one of the first things we perceive) it can be difficult to find a friend in a crowd if we don’t know what they are wearing, if they are the same height as everyone else, if the crowd is especially large, and so on. It is also interesting to note our reaction time when we do find our friend. How long does it take between the presentation of our friends face and our recognizing that we have found the right person?

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