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Psych 1000 - Sensation and Perception - 1 .docx

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Psychology 1000
Dr T Biggs

Lecture 1: Sensory and Perceptual Processes Sensation and Perception Sensation  The process by which our sense organs respond to and translate stimuli into nerve impulses sent to the brain Perception  Organizing the stimulus input and giving it meaning Stages of Sensation and Perception 1. Stimuli activate sensory receptors 2. Sensory receptors translate information into nerve impulses 3. Specialized neurons and analyze stimuli features 4. Stimulus pieces are reconstructed and compared to stimuli in memory 5. Perception is then consciously experienced Psychophysics: Sensitivity to stimuli  Absolute limits of sensitivity o Dimmest light in which we can see objects o Softest sound we can hear  Recognizing differences between stimuli, measure the difference between what you can and can’t sense o Smallest difference in brightness detectable o Recognizing differences between tones Stimulus Detection  The lowest intensity at which a stimulus can be detected 50% of the time  However, the environment contains a background level of stimulation for each sense and this level (the ADAPTION level) must be overcome if a stimuli is to be detected The Absolute Threshold  Going to plot the amount of positive responses at 50.  Generic chart for psychophysics.  At: 50% say it is there and 50% say its not – that is our Absolute Threshold  Measured in units of physical energy depending on the type of sensation  Below 50% we don’t count because it is below guessing, everything over that is better than guessing  You have to take the absolute limit because it is the limit between below and above guessing. Examples of absolute threshold for all your senses  However, the environment contains a background level of stimulation for each sense and this level (the Adaption level) must be overcome if stimuli is to be detected  Background contains a level of stimulation for each sense and this level needs to be overcome  Sometimes this signal will be able to overcome Differential Threshold  The amount of energy required to overcome the Adaption level  Is subject to variation with changes in circumstances Locke’s Experiment  Materials: 3 buckets/large bowls  Method: fill 1 with very hot water, 1 with cold water, 1 with tepid water.  Procedure: subject closes eyes – place one hand in hot and the other in cold for approx 3 minutes. Then place both hands in tepid water  Ask subject to report sensation for each hand separately  Instruct subject to open eyes  Although both hands are in the same water the sensations differ to the prior Adaptation, they adapted to the hot and cold water and it exceeded adaption level. Signal Detection Theory  Detection Criterion: A personal standard of certainty before a person will say that they detect a stimulus, brought into play when they report into you. o Affected by:  Conservativeness (require more info) or Boldness (require less info)  Increasing rewards for hits or costs for misses  If you say yes and it is there, if you say no and it is not there = hit  If you say yes and it is not there, if you say no and it is there = miss o Bold subjects show high hits and high false alarms o Conservative subjects show high misses and correct rejections Conservative high in these cells Bold high in these cells o However, Criterions can be manipulated by changing the payoff for each cell of the response matrix: going to create a bolder subject o This shows perception is, to some extent, a decision Subliminal Perception  A subliminal stimulus cannot be perceived consciously but do register in the nervous system o “Subliminal” advertising during a movie. o Exp. the watch now becomes associated with that guy. Consciously you are not aware of it. o OR Exp. that is why apples light up on Macbooks when you turn them on, they are present but you never actually think about it.  Research Results  Stimuli about threshold influence behavior much more than subliminal stimuli  Subliminal stimuli have stronger effects on attitudes  Effects may be die to placebo effects – think something is going on and might lead towards it. The Difference Threshold  The difference threshold (just noticeable difference or JND) is the smallest difference between two stimuli that people can perceive 50% of the time. o Weber’s Law: the JND is directly proportional to the magnitude of the stimulus with which the comparison is made, can’t sense the chance (e.g. 1/50for weight) o (won’t be able to tell the difference between 200 – 203 pound but on th the 204 pound you can tell the difference. Weber’s Law The smaller the fraction the less change is necessary to produce a JND. Thus only a 2% change is necessary to detect a difference in lifted weights Compared to a 33% change necessary for a change in the taste of salt to be notices. **The more of it you use the more you will need to use in the future to sense a difference. You need to have ________ to sense a difference Sensory Adaption (Habituation)  Sensory neurons respond to a constant stimulus by decreasing their activity, (you will become habituated to a certain level of salt in your food), the stimulus that is used in the senses will decrease their activity. You can reverse this by not using those stimulations. Sensory Systems: Vision Retina: multilayered tissue at back of the eyeball Optic Disk – a small blind spot with no receptors where the optic nerve exits the eyeball Fovea – small, central area of the retina where acuity is greatest, Lens: becomes thinner to focus on distant objects and thicker to focus on closer ones. Iris: Regulates the size of the pupil Pupil: adjustable opening controlling the amount of light entering the eye Cornea: transparent protective covering Vision: Photoreceptors  Rods: o Black and white receptors o Sensitive to dim light  Cones: o Located in Fovea o Color receptors ¼ mm Vision: Transduction  Absorption of light by photopigments produces a chemical reaction changing the rate of neurotransmitter release at the receptor’s synapse  The greater the change in release, the stronger the signal passed into the optic nerve Vision: Visual Pathways  At the level of the retina one the rod & Cone receptors have transduced the photonic energy into electrical impulses the information is then passed to bipolar cells and from there to ganglion cells  This process condenses signals from 130 million receptors to a few million bipolar cells to less than a million ganglion cells.  Lateral Summation: A major source of this condensing is due to the fact that as many as sex Rods may be connected from one bipolar cell and several bipolar cells may converge on a single ganglion cell.  This means that signals which originate with Rods have poorer resolution than signals from Cones which are connect 1 to 1 or 2 to 1 with bipolar cells. Factors which Influence Vision  Although we have sent he system reduced input from approximately 130 million to just under 1
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