Sensation and Perception

Transcription

1 Sensation v. Perception Sensation and Perception Chapter 5 Vision: p Sensation vs. Perception Physical stimulus Physiological response Sensory experience & interpretation Example vision research questions: How does the eye take light and transform it into a message the brain can understand? How do we see a stable world even though our eyes are constantly blinking and shifting? How do perceptual illusions trick the mind? Vision - cortex Physical properties of light Wavelength Hue Amplitude Intensity/brightness Mix of wavelengths Saturation 3 1

2 The Eye Transduction Process to translate light into an electrochemical message for the brain Blindspot demonstration Vision problems Accomodation = shape of lens changes to focus Flexibility lost with increased age Presbyopia Demo in text p

3 Photoreceptors Rods Concentrated in periphery of retina Low light ok No detail, no color Cones Concentrated in fovea Needs full light High visual acuity Color receptors The three main layers of the retina Dark adaptation Color theories Opponent-process theory Lilac Chaser dex.html Trichromatic theory 3

4 Negative afterimage Center-Surround Receptive Fields Allows brain to detect edges Text demo p155 Luminance and contrast Motion perception Phi phenomenon Max Wertheimer 1912 Motion via still images Motion illusions Motion aftereffect 4

5 Rotating Snake ex.html Think: What perceptual work is required by a baseball player to hit a baseball? Dynamic visual acuity: see moving object, see rotation of object Depth perception: see how far away it is Tracking: keep eyes fixed on moving object Object recognition: separate object from field Contrast sensitivity: see object color against background color Pick up on other cues specific to sport Gestalt principles of organization Laws of perceptual organization Figure vs. ground Object (or Pattern) Recognition How do we interpret lines and patterns as objects? Proximity Similarity Closure Good continuation Common fate 5

6 Which gestalt law? Biological motion Which gestalt law?? What are the depth cues? Depth perception Monocular cues Linear perspective Acuity Color and brightness Shadow or occlusion Relative height Relative motion 6

7 Binocular cues Retinal disparity Convergence Depth illusions Ames room Depth perception Pattern recognition Bottom-up processing Information from sensory receptors Top-down processing Information from knowledge and expectations Perceptual constancies Feature detectors Visual disorders Specialized receptors in visual cortex Simple cells Orientation specific Complex cells Movement, faces, etc. How does brain pull information together? Cell s responses Stimulus Agnosia: deficit in recognizing objects Book: The man who mistook his wife for a hat by Oliver Sachs Prosopagnosia (faces) Akinetopsia (objects in motion) What system Damage to occipital-temporal pathway Where system Damage to occipital-parietal pathway 7

8 Perceptual parsing Detect and identify primary 3d objects or geons (Biederman, 1987) Biederman s Geons Intersections are important to recognition Top-down processing Top-down processing 8

9 Tox-Doxn Pxocxssxng Perceptual problem solving: Impossible figures To xllxstxatx, I cxn rxplxce xvexy txirx lextex of x sextexce xitx an x, anx yox stxll xan xanxge xo rxad xt ix wixh sxme xifxicxltx Why are you able to read the sentence above? Psychophysics EXTRA slides Psychophysics Study relationship between stimuli and our psychological experience Light- brightness Sound- volume Pressure- weight Taste- sweetness 9

10 Thresholds Absolute Threshold minimum stimulation needed to detect a particular stimulus usually defined as the stimulus needed for detection 50% of the time Difference Threshold minimum difference between two stimuli that can be detected just noticeable difference (JND) Psychophysics Weber s Law: Perception of a difference between two stimuli, they must differ by a constant proportion light intensity- 8% weight- 2% tone frequency- 0.3% Sensory adaptation Diminished sensitivity with constant stimulation From the last class What is the blind spot and why does it exist? Rods and cones are receptor cells located mainly in the. are responsible for vision in dim light. are responsible for color vision when there is sufficient light. The negative afterimage of the flag or the lilac chaser support which theory of color? From the last class What are the 5 gestalt laws? Processing that is controlled by the physical message delivered to the senses is called processing. Processing that is controlled by one s beliefs and expectations about how the world is organized is called processing. What evidence supports Biederman s recognition by components theory? 10