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05 Sensation.docx

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Psychology 1000

Tuesday October 23, 2012 Scan: pages 150 to 158 Sensation - Psychophysics - Subliminal perception - Visual system What do Weber fractions tell you about sensation? Can we perceive subliminal messages? How does the visual system work? SENSATION - How do we perceive the world around us? - Psychophysics and psychophysiology Psychohphysics: relation between physical stimulus and psychological response Fechner: “Father” of psychophysics - Gave us methods and comparisons that we can do in order to measure psychological response - Can determine a just noticeable difference - JND: e.g., how much do I have to crank up the light source for you to notice and tell me that there is a JND? Threshold: - Value of a stimulus characteristic required to produce some response - Absolute threshold: lower limit - Difference threshold: amount of change for JND Absolute thresholds - Vision: candle flame at 50 km - Hearing: tick of a watch at 6 m - Taste: teaspoon of sugar in 8 litres of water - Smell: 1 drop of perfume in a 6 room apartment - Touch: wing of a fly falling on cheek from 1 cm Difference threshold: so what’s the relation? - E.g., brightness and perceived brightness - Not a 1 to 1 relation - Weber’s Law: size of a difference threshold relative to physical intensity of test is constant (ΔI/I=C) o E.g., if I = 50 dB and a JND is reported at 55 dB; 50 dB/55 dB = 1/10 - 1. With this constant, we can now predict other JNDs o E.g., what is a JND at 100 dB? ΔI = 1/10 x 100 = 10 dB; a JND would occur at  new test + 10 = 110 dB OR  new test – 10 = 90 dB - Hence value of JND is not constant - The relative difference is constant - 2. Can compare sensitivity of different systems o Vision (brightness): 1/60 o Kinesthesis (weights): 1/50 o Pain (thermal): 1/30 o Audition (middle pitch and moderate loudness): 1/10 o Pressure (skin): 1/7 o Smell (India rubber): 1/4 o Taste (salt): 1/3 Fechner’s law: sensation increases with the logarithm of intensity - S = k log I (compared to ΔI = CI) - More general and cognitively economic Steven’s power law: N - S = k log I - More predictive across a variety of sensations Subliminal perception: - Can we predict stimuli that are below threshold? - Is our behaviour affected by subliminal stimuli? - James Vicary (1957): claimed 50% increase in popcorn sales after he applied subliminal “cuts” to movies playing at the theatre (he bluffed!) - Caused concern about the use of subliminal “cuts” - However, in general, no evidence that subliminal cuts influence consumer behaviour - But, consider Bruce & Valentine (1986) o Priming: people recognized two related people about 100 msec faster - Fitzsimons et al. (2008) o 30 msec exposure to either Apple logo or IBM logo o Those who were exposed to Apple generated more creative uses of a brick o Perhaps Apple logo has an in influence on the subsequence task Sensory systems 1. Accessory structures (e.g., outers): for no other reason but to funnel sounds into the ear 2. Transduction: receptors 3. Coding: e.g., frequency 4. Interaction: physiological and psychological The visual system - Iris: controls the size of the pupil - Pupil: adjust light levels by contracting or dilating - Cornea: focuses the eye - Lens: focuses (but does not focus as much as cornea) - Vitreous humor: the “jelly” that inflates the eyeball and keeps shape consistence - Retina: where the image goes o Fovea: most sensitive part of the eye - Optic nerve: bunch of axons bundled together - Blind spot: nothing there for transduction Thursday October 25, 2012 Scan: pages 152 -158; 170 – 176 Visual processing - The Retina - Single cell recording - Lateral inhibition How do rods and cones work? How does the visual system enhance images? How can we explain phantom spots? Q: Let’s say you can barely distinguish 100 grams (test) of Swiss cheese from 105 grams. According to Weber’s Law, where should you expect a JND if I give you 300 grams as the new test weight? A: 315 g or 285 g Light > cornea, pupil, lens > ganglion cells (output to optic nerve) > bipolar cells > receptor cells > back of the eye Retina: - Ganglion cells (output to optic nerve) - Bipolar cells - Receptor cells Two types of receptor cells - Rod - Cones Between receptors and bipolars: horizontal cells - They are exclusively inhibitory - Responsible for “cleaning up” the image Between bipolars and ganglions: amacrine - Also exclusively inhibitory Cones are wider than rods; all located at the back of your eye; rods and cones: - Duplex theory - 120 million rods - 7 million cones Rods: operate at low intensity - Sensitive for brightness - None in Fovea (only in peripheral retina) - Monochrome (decode in black and white only) Cones: operate at higher intensities - “insensitive for brightness” - Concentrated in fovea - Full colour But how do rods and cones work? - Visual pigments at the end of all rods and cones o These pigments are photosensitive (breakdown when light hits them and generates an action potential) o In rods: rhodopsin o In cones: chlorolabe, erythrolabe, cyanolabe (for each primary color) - How to demonstrate this? o Dark adaptation: flash light into eyes – instantly blinded and retina is “bleached”; then, show them some light and ask them when they can see it again  Threshold vs. time in dark (minutes); absolute threshold  Cone recovery (recover first when retina is bleached)  Rods get more sensitive afterward – continuously gets more sensitivity o Spectral sensitivity: some cones are specifically sensitive to different colors Tuesday October 30, 2012 Finish: chapter 5 Perception - Lateral inhibition - Visual cortex - Gestalt laws Q: The neurons near the oval window are firing rapidly, while other
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