2007-10-18 - Perception
Perception is the interpretation of sensation. Perception is subjective, different, though there is sometimes an average subjective interpretation that seems to exist. You can see colors differently, even though the photons might be the same. Taste is subjective. These are rules and generalizations. Your perceptions are uniquely yours. WOMEN SEE RED. BE RED.
Thresholds
Threshold- passing point, keeping hay in a building. Absolute threshold- the point at which a stimulus can be detected 50% of the time. Wristwatch on a table - move to where you cannot hear it most of the time. The difference thresholds or Just Notable Difference (JND)- the minimal difference a person can detect between any two stimuli. Threshold is a point that you do not surpass, it is a limit, a constraint. For literature and discussion, thresholds can be passed, but not in the physiological case. These are measurements of your perception. When you are comparing stimuli, trying to decide at what point somebody begins to notice the difference, then that's JND. Suppose you're lifting a weight, a basic curl, and you've noticed a 5 lb weight, and what if you add an ounce? You don't notice. Add 2 ounches, you don't notice. Add 4 ounces, and you might notice it.
Suppose you had a tiny light in a dark room. At a certain threshold, for 10 times, you will notice the light only 50% even if you're trying because the light is faint, it's not as bright, it's not that you're not paying attention, it's that the light is just at the point where you can notice it, but you only notice it half the time. Nonconscious recognition means below the threshold.
These two measures measure the bottom point at which you begin perceiving, the other compares them.
See a flame 3 miles away on a clear dark night not 30 miles!. Hear the tick of a watch under quiet conditions at 20 feet. Taste 1 teaspoon of sugar in 2 gallons of water. Smell one drop of perfume diffused in a three bedroom apartment. Feel the wing of a bee falling on your cheek at a distance of 1 cm. These numbers were taken in the 1880s by the functionalists. In the 1880s they did not have the same measurement technology ... they were put more into a narrative, something the average person could understand. These are absolute thresholds, so all of this is half the time. What do you have to do to set up an experiment to make this true? You have to make sure that the person has 20/20 vision, you have to make sure the flame is burning at the same rate, burning at the same intensity and then there's flame, and what about phasing of the moons, or being within the city or not, etc. ? These are not true scientific descriptions ... they are historical. There are many variables to have to play with. You must know these thresholds.
Hypoglycemia, diabetics, pre-diabetics, --> are able to taste sugar more strongly than others.
Weber's law
Weber was the guy who thought about JND in the 1800s. Weber started thinking about, if you can measure threshold, you should be able to measure when people notice different stimuli. All it is: when you notice a difference between two stimuli, you stick with the JND name, and it's not complicated. He called it difference threshold: is the minimum amount by which stimulis intensity must be changed in order to produce a noticeable variation in sensory experience. This is a constant proportion- the change in perception is always in a constant proportion. So if you notice an extra 4 ounces, then you'd notice at 8 ounces, not at 5 pounds 3 ounces. So this is sort of discrete. Once you get the measurement, you will find it's a constant proportion.
Fechner's law
Fechner disagreed with Weber. So he generalized Weber's law into a natural logarithm. Weber says proportionality, and Fechner thought it was logarithmic (exponential, shifting). So he thought that instead of 5-5.4-5.8 you could feel possibly 5-5.4-5.6 or something. Fechner was the guy that made himself blind. Neither of these are right. Because perception is so subjective, you begin to expect a change, so your expectation changes whether or not you perceive it. Expectation is a factor.
Fechner was a professor at Leipzig in the 1800s. He came up with the psychophysical law - strength of sensation is proportional to the logarithm of stimulus intensity. Fechner came up with a philosophy that endowed consciousness to all matter. He used himself as a subject- burned his retinas out by staring at the local star.
Hermann grid, visual test
The Hermann grid tests your blind spot - the retinal ganglion cells help form the optic nerve which carries information to the brain. ON region responds to an increase in light while the OFF region responds to a decrease in light. This is one of the supports for the theory that you have an 'opponent process' happening in your eye, i.e. cones and rods that are paired together, but when they work together, one is on and the other is off, so only one could send a stimulis at a time.
Young-Helmholtz Trichromatic Theory
- You have three color channels. Those colors are red, green and blue and when we stimulate this combination we see other colors.
Opponent-Process Theory
- You have pairs of receptors that work together. One is on, the other is off. The pairs are simple: red-green pair, blue-yellow pair, and a black/white pair (rods instead of cones). In order to blend colors and see colors, you would have these going on and off that sends a code to the brain saying what color you are seeing, basically. Every color you see is still a blend. But for the opponent-process theory, it's the pairs working together to help you sort it all out. They have proven that these two theories are true.
They've found that the YHT theory and the OP theory are both right, and for the range of colors that we see, we have to use pairs that work together and blending that takes place.
Selective attention- when we focus our awareness only on limited aspects of all that we are capable of experiencing. This is where we "block" out some signals.
Gestalt theory- meaning whole psychology, how we organize our sensations into perceptions. One of the ways to organize your perceptions is via deciding, decision-driven organization. Right now, because you're in a class, you are focusing on certain stimulation, if not you would be focusing on other things ... if it was social, you would not be focusing on the board, but instead other things. Gestalt says that it is a choice. There's also form perception.
Diet changes can fix autism at young age? Autism as an industrial disease? ADHD and Autism -> diet driven?
Form perception organization.
Figure/Ground- figure are words and the ground is the white paper.
Grouping- stimuli together, perceived whole differs from the sum of the parts.
Easy to lump stuff together when you perceive things. People with really good memories tend to lump ideas together, or do things like, a grocery list, people with really good memories, would think to lump all of the vegetables together, and so they would know all the vegetables.
Grouping by proximity- perceive things that are closer together as tending to have some type of cohesion. You can do a test on this on Monday/Tuesday. Put some coins closer together or far apart, see how much they think there is.
Grouping by similarity- people will group things for simuliar objects
Continuity - smooth, continuous pattern
Connectedness - uniform and linked, spots, lines are a single unit
Typed words are a bunch of pixels.
Closure - the triangle optical illusion with the three pacman, you just assume there's a line where there really isn't
Binocular and monocular cues
Binocular cues- so these are cues that require both of your eyes or trick your eyes.
Retinal disparity- retinas receive slightly different images of the world, and when the brain compares these two images, they make one picture. Think about 3D movies. Or stand 10 ft apart, toss a ball back and forth.