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Chapter 5

Day 14 - Chapter 5 Sensation.docx

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Western University
Psychology 1000

Psych1000 Day 14 - Sensation Agenda  Psychophysics  Subliminal perception  Visual system Prep Questions - What do Weber fractions tell you about sensation? - Can we perceive subliminal? subliminal messages? - How does the visual system work? How do we perceive world around us? - Psychophysics: ex. how do we code senses psychologically? - Psychophysiology (receptor level, what happens to the eye?) Psychophsyics: relation between physical stimulus & psychological response Fechner: “father of psychophysics: - Determined a just noticeable difference (JND) - It’s hard to measure psychological intense, BUT you can measure the difference of sensitivity - Ex. turn the light on, you tell me your sense, turn the intensity of light higher, you tell me the difference Threshold: the value of stimulus characteristic required to produce some response - Absolute threshold are the lower limit of the threshold - Ex. vision: candle flame at 50 km on clear dark night (most sensitive sense in a human) - Hearing: tick of an old watch @ 6m (second most sensitive sense in human) - Taste: tsp of sugar in 8L of water - Smell: 1 drop of perfume in a 6rm apt - Touch: wing of a fly falling on check from 1cm - Difference threshold: amount of change that’s necessary for JND o ex. how much change you need to notice the difference - So what’s the relation between psychological stimulation and actual stimulation? o Ex. brightness & perceived brightness o This is NOT a 1:1 relation  Ex. doubling brightness does NOT mean you get doubling in perceived brightness - **Weber’s Law: size of difference threshold relative to physical intensity of test is constant - = C (size of difference of different threshold in relation to the intensity of the stimulus is constant) o If I = 50dB, JND = 55dB o 55-50/50 = 1/10 = C o Constant for this stimulation situation is 1/10 o You can predict other JND’s  ex. what’s a JND @ 100 dB?  ΔI /100 = 1/10  ΔI = 100  A JND would occur @ new test + 10 = 110 dB OR  New test – 10 = 90 dB o Note: the value of JND is NOT constant, but the relative difference is constant - Can compare sensitivity of difference systems o The smaller the ΔI, the better (the more sensitive) if the constant - Vision (brightness) = 1/60 - Kinesthesis (weights) = 150 - Pain (thermal) = 1/30 Psych1000 Day 14 - Sensation - Audition (mid Pitch; Mod. Loud) = 1/10 (more sensitive to low frequency than high pitches) - Pressure (skin) = 1/7 - Smell (India rubber) = ¼ - Taste (salt) = 1/3<<
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