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Chapter 6.docx

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Wilfrid Laurier University
Kris Gerhardt

1 IntroPsych Ch06 Sensation Perception 2 Why study S & P • Sensation – What takes place from the sensory receptors to the primary projection areas • Perception – Everything beyond that • Importance of the process – We construct the world around us and therefore we bias our own perceptions 6 Signal Detection Theory – Detecting a stimulus requires a judgment about its presence or absence • 2 processes work at detection tasks – An initial sensory process – A decision process – will reflect personal bias • Experimental procedure • 2 kinds of errors & 2 kinds of CR – False Alarm & Miss – Hit & Correct Negative (Response) • Factors affecting Response Bias – Expectations – Motivations • i>c 7 Signal detection theory (reference figure in other document) 8 Anatomy of Visual System (F. 4.8) 9 The Eye and Light • Path of Light – Cornea – transparent membrane that protects eye – Aqueous humor – gel layer – Pupil (is clear) – size changes to allow more or less light – Lens – takes in light, bends the light rays to focus them •Ciliary muscles – Vitreous humor – Retina – (three layer structure, covers inside surface of your eye) ganglion cells, cones and rods • 10 Cross section of the retina (F. 4.10) 11 The Retina • Cones (responsible for light vision, not sensitive to light) – 6 million (in each eye) – most in the fovea 1 – Daylight vision – High acuity vision – allows us to see fine detail – Provide info brain uses to see colour – 3 kinds of cones (Red, Green, Blue)  Red = long wavelengths, green = medium wavelengths, blue = short wavelengths. • Rods – 150 million (each eye) – everywhere except the fovea – Night vision – too sensitive for daylight vision – Low acuity – far less detail – No colour information – Sensitive to movement – **Red lights in plane cockpit/car (red lights shouldn‟t turn rods off, so you use day & night vision) 12 The Retina con’t • Distribution of rods & cones explains day and night vision – Colour & detail seen in center of visual field – Not so much in periphery • The Blind Spot – Where optic nerve leaves the eye • Eye to Visual cortex – Activity from rods/cones translated to nerve impulses – Optic nerve to thalamus to visual cortex 13 Perception of Colour • What determines the colour of an object? • Colour is NOT a physical property • Colour vision needs 2 sets of cone pigments – Hue; Saturation; Brightness – 2 million colour gradients can be sensed 14 2 Theories of Colour Vision (F. 4.23) 15 Trichromatic Theory • i>c • Any colour can be produced by mixture of 3 widely separated colours – Suggested red, green, blue • Accounts for complementary colours – Additive mixture – Subtractive mixture • Gray occurs when all 3 receptors are stimulated equally • Also explains negative after-images • Problem with trichromatic theory is that it suggests that colourblindness is caused by certain cones not working (such as red receptors), which is incorrect. (Most people are red/green colourblind, if you can‟t see either red or green, you wouldn‟t be able to see any colour because you need to compare the blue with something else). Therefore their colourblindness theory is wrong. 16 Fig. 20 17 Afterimages 18 Opponent Process Theory • Yellow seems to be a psychological primary – Yellow fits between Green and Red • 4 primaries arranged in opposing pairs – Red  Green & Blue  Yellow 2 – Presence of Red – increased activity for Red, decreased for Green (no greenish-red) 3 Another receptor for brightness – Black/white • Negative afterimages; Complementary colours • Colourblindness 19 Dual Process Theory 20 Punchline • Physiological research located 3 receptor types – support for trichromatic theory • Cells in the optic tract – cells that respond to light, excitation/inhibition – Support for opponent process • Different levels, different mechanisms 21 Other phenomenon • Colour Blindness (far more common in males) – Monochromats – no perception of colour at all – Protanopia (no red cone function); Deuteranopia (no green cone); Tritanopia (no blue cone) 22 Colour Deficient Vision • Trichromats – Normal colour vision • Dichromats – Deficient in one system (red-green is most common) • Monochromat – Sensitive to black-white only 23 Perception of Form • Information sent to brain is not a „picture‟ • Despite continual change in visual field, we perceive coherent objects • Wired in perceptual abilities – Is perception more nature or nurture • Gestalt organizing principles – Innate rules of perceptual organization – Figure vs ground; Similarity – Continuity; Proximity; Closure 24 Figure (what you focus on) vs. Ground (background) 25 Perceptual Organization • Figure and Ground organization of the visual field into objects (figures) that stand out from their surroundings (ground) 26 Gestalt Grouping Principals • Fundamental unlearned tendency • Law of Pragnanz (the law of good figure) • Proximity – grouping things that are close together • Closure – closing off figures (man on a horse made of shapes, or imagining something in clouds) • Continuity - straight lines (making connections) • Similarity – grouping things that are similar to each other (based on colour, shape, size) 4 • Common Fate – combination of continuity and similarity • Familiarity • Figure Ground 27 Continuity 28 Proximity 29 Similarity 30 Closure 31 Common Fate 32 Perceptual Constancies • Perceptions remain constant despite shifts in retinal image • • Position constancy – despite head/eyes moving, we perceive the position of objects as fixed in place • Colour Constancy – perceive colours in environment as unchanging (despite lights turning on/off) • Shape Constancy – knowledge that objects shape is unchanging • Size Constancy - knowledge that objects size is unchanging 33 Shape, size constancy & depth • 2 dimension image on retina – But 3 dimension view of world • Monocular cues (one eye or beyond 30m, about 100ft) – affects depth perception – Accommodation • Binocular – Convergence (cross-eyed, eyes move together); Retinal Disparity (difference between image on right eye and image on left eye). • External cues – Previous familiarity (Relative Size); Interposition; Texture gradient (smooth objects look farther away); Aerial perspective (looking down from high above); Linear perspective (parallel lines seem to move toward each other as they move farther away – 2 straight lines turned in); Shadows & Illumination – Motion Parallax (objects close move quickly in opposite direction, objects far move slowly in same direction) ex: driving in a car, looking at guardrail vs. looking at moon. 34 Illusions • Context can produce illusions 35 Context – Substantial role in perceptual interpretation – Important in perceiving spoken languages – Important for touch – Importance for vision • Schemas •Patterns of thinking to make environment predictable – Beliefs and expectations – Objects, people (personality, introvert, extrovert), situations (social behavior at funeral vs. party) – Increase speed and efficiency of perception – Can lead to an increase in perceptual errors – *Allows you to anticipate what will come next, like shortcuts (for example, watching movies) 36 Motivation • See what we expect to see
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