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Chapter 5

Psychology chapter 5.doc

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Psychology- The study of human behaviour Chapter 5 Perception Sensory processing Sensation is the detection of simple properties of stimuli such as brightness, colour, warmth and sweetness. Perception is the detection of objects, their locations, their movements, and their back- grounds. Transduction Transduction means leading across and is the process by which the sense organs convert energy from the surroundings into neural activity. Each sense organ responds to a particular form of energy from the surroundings Receptor cells release chemical transmitter substances that stimulate other neurons, therefore altering the rate at which they fire. The somatosenses do not need the presence of receptor cells to fire however some cells require the receptor cell in order to send the electrochemical impulse Sensory Coding How is it that even though the same action potential is sent through all neurons, they all manage to code for millions of things? what makes each signal special from the oth- ers? A code is a system of symbols or signals representing information. this is very similar to stop signs and traffic lights There are two types of coding involved in the brain: Anatomical Coding is the ability for the brain to interpret the location and type of sen- sory stimulus according to which incoming nerve fibers are active. If you were to rub your eye you would give it a non visual stimulus however the brain will interpret the sig- nal coming from the eye as light, this is why you see stars Temporal coding is the condition of information in terms of time. The simplest form is rate. The intensity of the stimulus is not measured by magnitude, no signal can be stronger than the other. The only difference is the rate of fire and depending on that, you will feel pain worse or less. Psychophysics Psychophysics is the systematic study of the relationship between the physical charac- teristics of the stimuli and the sensations they produce. (Physics of the mind). There are two ways of measuring peoples sensations: The principle of just noticeable difference was what Ernst Weber measured when doing his experiments. He wanted to know the smallest change in the magnitude of a stimulus that person can detect. According to Ernst, the difference between weights for people to notice the difference was a 1/40 ratio. If the weights were differed by more than 1/40, then the people would notice. brightness had a ratio of 1/60. These fractions were known as weber Fractions. Gustav Fencher used this to test peoples sensations to light brightness by slowly changing the brightness of one of two lights until someone would notice a difference. A graph was then constructed. The jnd increases with the intensity of the stimulus. The resulting graph is a logarith- mic function. IF webers principle did not hold the graphs points would scrunch up near the end of the graph Stevens suggests that the physiological magnitude of the stimulus is measured by: S= KI^b Where k is a constant and (I) is intensity raised to the power b. b is a number between zero and one. If the value is greater than one, then the graph ignores webers principles. Signal Detection Theory states that every stimulus requires discrimination between signal (stimulus) and noise (background). The threshold is the line between not perceiv- ing and perceiving.the just noticeable difference can also be known as the difference threshold. The absolute threshold is the minimal value that a stimulus can be detected. Overall the threshold is the point at which the subject detects the stimulus 50% of the time. Some experiments are done where it is tested if you hear a sound or not. At this point however, your response bias may play a role in whether you say yes or no. hits say yes you heard the sound Misses say no you did not detect a sound Correct negatives are saying no when the stimulus is not present False alarms are saying yes when the stimulus is not present Payoff reduces the response bias, one that is payed a dollar for every hit will say yes ALL the time. One that is fined a dollar for every false alarm will not respond whatsoev- er. This payoff affects the way people will respond The ROC (receiver operating characteristic) shows performance when the sound is diffi- cult to detect. Vision Light Wavelength is the distance between one crest and the other in a wave. Wavelength in visible light ranges from 380 nm to 760nm. The different wavelengths have different colours The entire spectrum of waves is known as the electromagnetic spectrum, the part we can detect are known as the visible spectrum. The eye and its functions The transparent cornea forms a bulge at the front of the eye and admits light The sclera is a tough white membrane that coats the rest of the eye The Iris consists of two muscles that control the contraction and dilation of the eye. The brain controls these muscles and thus regulates the size of the pupil
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