Lecture 6-Sensation

Lecture 6-Sensation - Sensation and Perception T r a n s d...

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Unformatted text preview: Sensation and Perception T r a n s d u c ti o n fr o m p h y s i c a l to n e u r a l B a g o f T ric k s : Perceptual Constancy Depth Perception Organizing Principles Sensation -- experience associated with a simple stimulus (i.e., a light, a sound) Perception--subsequent organization of sensory in f o r m a tio n a n d in te r p r e ta tio n s e x tr a c te d f r o m it. So... the difference is simply one of degree. P e r c e p tio n is in te r p r e ta tio n o f s e n s a tio n . Sensation & Perception Processes Bottom Up processing --> <-- Top Down Processing MIND TOP DOWN DOWN Perception Interpretation Sensation STIMULUS STIMULUS BOTTOM UP Neural Coding - Transduction S e n s a tio n is c o d e d f o r in te n s ity ( s tr o n g v s . w e a k ) and quality (e.g., red vs. blue, foul vs. pleasant). T y p ic a lly , m u c h o f th is c o d in g h a p p e n s a f te r r e c e p to r s , a t s ite s in th e c o r te x . S e n s e s in te g r a te in p u t a c r o s s r e c e p to r s a n d o v e r tim e to r e c o g n iz e p a tte r n s . Visual Processing The Retina The Retina R o d s & C o n es Rods--operate under low illumination and are achromatic -night time receptors. Cones--operate under high illumination. Chromatic. Packed around fovea -daytime receptors. Visual Pathways Hubel & Wiesel’s Experiment Some cells in the visual cortex respond only to certain types of visual information For example, a diagonal line moving up and down These cells are called feature detectors Trichromatic Theory T. Young (1802) & H. von Helmholtz (1852) both proposed that the eye detects 3 primary colors red, blue, & green All other colors can be derived by combining these three Afterimages FATIGUE FATIGUE With fatigue, signals green Sensory Adaptation R e p e a te d s tim u la tio n o f a p a r tic u la r r e c e p to r le a d s to r e d u c e d r e s p o n d in g . Bag of Tricks How do we use limited sensory data to identify complex perceptions? - Assume constancy of objects in world - Use cues to reveal depth of field Use - Use organization to group elements Use Organization: Gestalt Psychology Gestalt means “whole” “whole is greater than sum of the parts.” Laws of Pragnanz = Laws of organization. Gestalt Principles P r o x im ity Seeing 3 pair of lines in A Seeing columns of orange and red dots in B Seeing lines that connect 1 to 2 and 3 to 4 in C Seeing a horse in D S im ila r ity C o n tin u ity C lo s u r e s Perceptual Constancy A s s u m e o b je c ts in th e w o r ld a r e s ta b le . S e n s a tio n s ( th e d a ta ) c h a n g e , b u t p e r c e p tio n s r e m a in th e s a m e . A s s u m e c o n s ta n t o v e r o b s e r v e r m o v e m e n ts S h a p e c o n s ta n c y S iz e c o n s ta n c y Shape Constancy Even though these images cast shadows of different shapes, we still see the quarter as round Size Constancy A specially-built room that makes people seem to change size as they move around in it The room is not a rectangle, as viewers assume it is A single peephole prevents using binocular depth cues Cues to Depth Perception Cues Monocular Cue? Monocular Cue? Monocular Cue? Monocular Cue? W h at C u es D o Y o u S ee? Julian Beever - 3D Pavements Context Effects The same physical stimulus can be interpreted differently We use other cues in the situation to resolve ambiguities Is this the letter B or the number 13? Perceptual Set L o ch n es s M o n s ter o r a T ree T ru n k ? Perception is an Active Process “It may take a magician to pull a rabbit out of a hat, but we all possess sufficient magic to pull a duck out of a rabbit.” R. N. Shepard, 1990 Cultural Influences on Depth Perception Top Down: Top Perceiving what you expect to see When asked by his dentist, “Where does it hurt?” …philosopher Bertrand Russell replied: “In my mind, of course.” ...
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