Psychology 1000 Lecture Notes - Lecture 5: Gestalt Psychology, Middle Ear, Auditory Cortex

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24 Jan 2017
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Sensation & Perception
Lecture 5 Notes
Sensation and Perception
o Sensation
The process by which our sense organs respond to and translate
stimuli into nerve impulses sent to the brain
o Perception
Organizing stimulus input and giving it meaning
Stages of Sensation and Perception
o Stimuli activate sensory receptors
o Sensory receptors translate information into nerve impulses
o Specialized neurons analyze stimuli features
o Stimulus pieces are reconstructed and compared to stimuli in memory
o Perception is then consciously experienced
Psychophysics: Sensitivity to Stimuli
o Absolute limits of sensitivity
Dimmest light in which we can see objects
Softest sound we can hear
o Recognizing differences between stimuli
Recognizing differences between tones
Stimulus Detection
o The absolute threshold
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 ADAPTATION level)
must be overcome if a stimulus is to be detected
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the amount of energy required to overcome the adaptation level is
known as the DIFFERENTIAL THRESHOLD, and it is subject to variation
with changes in circumstances
o Locke’s experiment
Materials: 3 buckets/ large bowls
Method: fill 1 with very hot water, fill 1 with very cold water, 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
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Although both hands are in the same water the sensations differ
due to the prior ADAPTATION
Signal Detection Theory
o 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 of misses
o Bold subjects show high hits and high false alarms
o Conservative subjects show high misses and correct rejections
o However, criterions can be manipulated by changing the payoff for each
cell of the response matrix
o This shows perception is, to some extent, a decision
Subliminal Perception
o A subliminal stimulus cannot be perceived consciously but do register in
the nervous system
“subliminal” advertising during a movie
o stimuli above threshold influence behavior much more than subliminal
stimuli
o subliminal stimuli have stronger effects on attitudes
o effects may be due to placebo effects
The Difference Threshold
o the difference threshold (just noticeable difference of 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 (i.e. 1/50 for weight)
Weber’s Law
o the smaller the fraction, the less change is necessary to produce a JND
o thus, only a 2% change is necessary to detect a difference in lifted weights
o compared to a 33% change necessary for a change in the taste of salt to
be noticed
Sensory Adaptation: Habituation
o sensory neurons respond to a constant stimulus by decreasing their activity
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