Psychology 1000 Lecture Notes - Subliminal Stimuli, Circadian Rhythm, Detection Theory

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9 Feb 2013
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Sensory and Perceptual Processes
Everyone experiences a different reality when someone dies so does their
universe
Sensation the process by which our sense organs responds to and
translate stimuli into nerve impulses sent to the brain
Perception organizing the stimulus input and giving it meaning based on
prior experience, expectations, etc.
Stages of Sensation and Perception
Stimuli activate sensory receptors
Sensory receptors translate information into nerve impulses info
received in one form of energy is transduced into a different form
Specialized neurons analyze stimuli features
Stimulus pieces are reconstructed and compared to stimuli in memory
Perception is then consciously experienced
Psychophysics: Sensitivity to Stimuli
Physics of energy detection
Absolute limits of sensitivity
o Dimmest light in which we can see objects
o Softest sound we can hear
Recognizing differences between stimuli
o Smallest difference in brightness detectable
o Recognizing differences between tones
Stimulus Detection
The Absolute Threshold
o The lowest intensity at which a stimulus can be detected 50% of
the time
o However, the environment contains a background level of
stimulation for each sense and this level (the ADAPTATION level)
must be overcome if a stimuli is to be detected
o Ex. noise = competing sensations for the same sensory organ
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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
Locke’s Experiment
o Materials: 3 buckets/large bowls
o Method: Fill 1 with very hot water, one with very cold water, one
with tepid water
o 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 adaptation.
Signal Detection Theory
Decision criterion a personal standard of certainty before a person will say
that they detect a stimulus can contaminate results
o Affected by conservativeness or boldness, increasing rewards for hits
or costs for misses
o Bold subjects show high hits and high false alarms
o Conservative subjects show high misses and correct rejections
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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
A subliminal stimulus cannot be perceived consciously but do register in the
nervous system
o “Subliminal advertising” in movies product placement
Subliminal Perception Research Results
o Stimuli above threshold influence behaviour much more than
subliminal stimuli
o Subliminal stimuli have stronger effects in attitudes
o Effects may be due to placebo effects
The Difference Threshold
The difference threshold (just noticeable differences or JND) is the smallest
difference between 2 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 comparisons is made (ex. 1/50 for weight
1/50 of the sample weight must be added to the comparison weight
before you can sense the difference)
The smaller the fraction, the less change is necessary to
produce a JND
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 noticed
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