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Lecture 14

PSYCO 104 Lecture 14: PSYCH 104 – LECTURE #14 – Sensation and Perception Pt. II

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Eric Legge

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PSYCH 104 – LECTURE #14 – Sensation and Perception Pt. II
Psychophysical Scaling
oEverything is relative in perception – cannot measure things using absolute
Fechner’s Law: Subjective sensation is proportional to logarithm of
stimulus intensity
Constant increments in stimulus intensity produce smaller and
smaller increases in perceived magnitude of sensation
oEg. Dark to one light turned vs one light to two lights vs.
oSignal Detection Theory: Assumes stimulus detection is not based on fixed
absolute threshold but rather affected by rewards, punishment, expectations
and motivations factors
Involves decision processes as well as sensory processes
Decision criterion: Potentially changing standard of how certain a
person must be that a stimulus is present in order to report its presence
Approximate Absolute Threshold
1. Vision: Candle flame 50 km away on clear, dark night
2. Hearing: Tick of watch 6m away under quiet conditions
3. Taste: Single teaspoon of sugar in ~7.5L of water
4. Smell: One drop of perfume diffused in large apartment
5. Touch: Wing of fly or bee falling on cheek from distance of 1cm
Perception Without Awareness
oSubliminal Perception: Registration of sensory input without conscious
Subliminal stimulus: Received by senses but not perceived consciously
Began with James Vicary (1957) and the “Eat Popcorn” ad
displayed in films
oResulted in 58% increase of popcorn sales
oSuggests some forms of subliminal perception can influence our behaviour in
some situations
Strobe and Claus (2006): “Lipton Iced Tea
Massar and Buunk (2009): “Attractiveness and Jealousy”
Saw different types of “attractive” bodies, then put in a jealous
situation and jealousy response monitored
Due to cognitive functions and not just stimuli
Sensory Adaptation: Diminishing sensitivity to unchanging stimulus with passage of
time as sensory neurons habituate to stimulation
oAdaptive process: Keeps us attuned to changes in environment rather than
Bottom-up processing: Perceptual processing that beings with analysis of individual
elements of stimulus and works up to brain’s integration of them into an unified
oDetects different stimuli, then builds “bottom-up” from stimuli
oDriven by activation of sensory receptors (individual stimuli) then passed to
higher, more complex levels of perceptual system
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