Psychology 1000 Lecture Notes - Cornea, Ossicles, Thalamus
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9 Nov 2011
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Tuesday October 25th
Sensory and Perceptual Processes
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:
• Stimuli activate sensory receptors
• Sensory receptors translate information into nerve
impulses
• Specialized neurons analyze stimuli features
• Stimulus pieces are reconstructed and compared to stimuli
in memory
• Perception is then consciously experienced
Psychophysics: Sensitivity to Stimuli
• Absolute limits of sensitivity
- Dimmest light in which we can see objects
- Softest sound we can hear
• Recognizing differences between stimuli
- Smallest difference in brightness detectable
- Recognizing differences between tones
Stimulus Detection
• The Absolute Threshold
- The lowest intensity at which at 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
Stimulus Detection
• The amount of energy required to overcome the Adaption
level is known as the DIFFERENTIAL THRESHOLD and it is
subject to variation with changes in circumstances
• Locke’s experiment
- Materials: 3 buckets/large bowls
- Method: fill 1 with very hot water, fill with very cold water,
and fill 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 due to the prior ADAPTION.
Signal Detection Theory
• Decision criterion: A personal standard of certainty before a
person will say that they detect a stimulus
• Affected by: conservativeness or boldness, increasing
rewards for hits or costs for misses
• Bold subjects show high Hits and High False alarms
• Conservative subjects show high misses and Correct
rejections