chapt. 4 PSYCH - Chapter 4 Sensation and Perception...

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Chapter 4: Sensation and Perception -- Psychophysics Psychophysics » Psychophysics: » The study of how physical stimuli are translated into psychological experience » Stimulus: » Any detectable input from the environment » What is the weakest detectable stimulus? » Absolute threshold » Minimum amount of stimulation that an organism can detect » E.g., smallest amount of light, or the faintest touch that an organism can detect » Arbitrarily defined as the stimulus intensity that is detected 50% of the time » Just Noticeable Difference (JND) » Smallest difference in the amount of stimulation that specific sense can detect » (Absolute threshold is the JND from nothing) » E.g., Stereo volume at 8, need to turn it up a greater amount to notice difference in loudness, than if your stereo was at 2 » Volume 8 to 9 not likely noticeable, volume 2 to 3, however is. » Weber’s Law » The size of the JND is a constant proportion of the size of the initial stimulus » Constant expressed as a Weber fraction » E.g., Weber fraction for lifting weights is 1/30 » …If you are lifting a 200 pound weight, the weight would need to increase by (200 * 1/30) = 6.7 pounds, to notice the difference » Subliminal Perception » Literally perception without awareness » “below the threshold” » E.g., “Eat Popcorn” imposed in film reportedly increased popcorn sales… » Small but legitimate effect, but claims likely to be exaggerated » E.g., Krosnick (1992): subjects subliminally presented scenes of varied emotional tone (positive vs. negative) had significantly different attitudes toward target person » Sensory adaptation » Gradual decline in sensory sensitivity due to prolonged stimulation » E.g., kitchen garbage smells, then after a few minutes don’t notice it…
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» We are tuned to changes, rather than constants in sensory input Vision » Light is the stimulus energy necessary for vision » Electromagnetic energy » Properties of light waves related to vision » Wave amplitude = brightness » Wave length = hue » Wave purity = saturation » Humans can see only a limited portion of the electromagnetic spectrum Electromagnetic Spectrum » How does vision take place? » Two broad extremely complicated processes: » Sensation: » Stimulation of the sense organs (i.e., eyes), by sensory stimulation (light energy) » Perception » Processing, analysis, and interpretation of incoming sensory input (i.e., what the brain does) Sensory Processes of Vision » Light enters the eye and an image is cast on the retina. » Light energy is converted into neural impulses. » “Transduction” – to convert one type of energy into another type of energy (e.g., light into electrical impulses) » Neural impulses, containing sensory information, travel to the brain.
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This note was uploaded on 01/30/2009 for the course PSYCH 110 taught by Professor Olver during the Spring '09 term at University of Saskatchewan- Management Area.

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chapt. 4 PSYCH - Chapter 4 Sensation and Perception...

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