PowerPoint  Presentation C h a p t e r 4 S E N S A T I O N & P E R C E P T I O N P S Y C H O L O G Y T h i r d E d i t i o n by Drew Westen John Wiley & Sons, Inc.

Lecture Outline n Sensation versus Perception n Psychophysics n Vision n Skin Senses n Perceptual Organization © 2002 John Wiley & Sons, Inc.

Sensation and Perception n Sensation is the process by which the body gathers information about the environment n Perception is the process by which the brain organizes and interprets sensory information  Sensation and perception are akin to two sides of the same coin  Perception is an active process Ambiguous figures give rise to different perceptions © 2002 John Wiley & Sons, Inc.

Basic Principles n Three principles emerge with regard to sensation and perception:  There is not a one-one correspondence between physical and psychological reality  Sensation and perception are active processes  Sensation and perception are adaptive © 2002 John Wiley & Sons, Inc.

Common Features of Sensory Systems n Sensory receptors  Translate physical stimulation into neural signals (“transduction” process)  Detect physical energy (e.g. light, sound waves) n Each system has a minimum amount of energy required to activate the system (termed the threshold) n Sensation involves decision making n Sensory systems are sensitive to changes in stimulation level © 2002 John Wiley & Sons, Inc.

Thresholds n Sensory receptors are tuned to a particular form of energy  Auditory receptors in the ear code for sound pressure changes, not for light n Sensory systems require a minimum amount of energy for activation (absolute threshold)  Just-noticeable difference (JND): The minimum difference in stimulation that is just noticeable Weber noted that the JND is a fraction of the original stimulus intensity: the fraction is different for different senses © 2002 John Wiley & Sons, Inc.

Weber’s Law © 2002 John Wiley & Sons, Inc.

ROC Curves © 2002 John Wiley & Sons, Inc.

Vision n The eye detects electromagnetic radiation (light)  Vision is functional Allows for detection of movement (predator or prey?) Allows for detection of color (ripe or spoiled?) n Light detection is useful because: Light travels rapidly (no delay, unlike hearing) Light travels in straight lines (no distortion) Light interacts with the surfaces of objects in the environment (is reflected or absorbed) © 2002 John Wiley & Sons, Inc.

Electromagnetic Spectrum © 2002 John Wiley & Sons, Inc.

Details of the Human Eye © 2002 John Wiley & Sons, Inc.

Details of the Retina Photoreceptors Light Impulses produced by light © 2002 John Wiley & Sons, Inc.

Transduction of Light n Light travels through the retina to impinge on photoreceptors at the back of the eye  Light bleaches a pigment contained within the photoreceptors: Bleaching leads to a graded receptor potential that eventually produces an action potential in the ganglion cell  Two types of photoreceptors Cones: found in center of retina (fovea) and are sensitive to fine detail and color Rods: found in periphery of retina and are sensitive to movement but not fine detail © 2002 John Wiley & Sons, Inc.

Receptive Fields  Receptive field: That aspect of the external world that produces a change in firing rate of a given sensory cell  Insert a microelectrode into a retinal ganglion cell: then record potentials as various stimuli are shown onto the cell Center-surround shape © 2002 John Wiley & Sons, Inc.

Visual Pathways in Brain: “Where” versus “What” © 2002 John Wiley & Sons, Inc.

Perception of Color n Color is a psychological perception  Three dimensions of color: Hue is the apparent color of an object (blue) Brightness is the intensity of a color Saturation is the purity of the color  Three different types of cones are found in the eye Each is sensitive to different wavelengths of light –S-cones: blue –M-cones: green –L-cones: red © 2002 John Wiley & Sons, Inc.

Retinal Cones Absorb Different Wavelengths of Light © 2002 John Wiley & Sons, Inc.

Color Vision Theories n Young-Helmholtz:  Color is explained by differential activation of 3 color elements in eye Could not account for negative color afterimages n Hering: Opponent-Process Theory  Colors are derived from activity of 3 antagonistic systems Black-white Red-green Blue-yellow © 2002 John Wiley & Sons, Inc.

Negative Color Afterimages Stare at the globe for 10 seconds and then look away at a white surface © 2002 John Wiley & Sons, Inc.

Skin Senses n Receptors are localized within the skin to detect physical stimuli in the outside world n Three classes of skin receptors:  Touch: physical contact of objects with the skin  Temperature of objects  Pain: destruction of skin tissue © 2002 John Wiley & Sons, Inc.

Skin Receptors © 2002 John Wiley & Sons, Inc.

Pain n Pain is a source of information that relates to tissue destruction  Force  Heat  Chemical n Pain is a adaptive to a degree (motivates behaviors to terminate the source of the pain) n Pain is influenced by  Cultural beliefs  Emotional states  Exogenous drugs (opiates)  Internal transmitters (endorphins) © 2002 John Wiley & Sons, Inc.

A Demonstration of Reversible Perception © 2002 John Wiley & Sons, Inc. (Figure adapted from Boring, 1930, p. 42)

Gestalt Principles of Form Perception A: Similarity B: Proximity C: Good Continuation D: Simplicity E: Closure © 2002 John Wiley & Sons, Inc.

Monocular Depth Perception Cues n Interposition: One object blocks another n Linear perspective: Parallel lines converge in the distance n Texture gradient: Texture of distant objects appears to be finer rather than coarser n Shading: 3D objects cast shadows n Aerial Perspective: Far objects are fuzzy n Familiar size: Familiar objects that appear small are inferred to be distant n Relative size: When looking at 2 objects of known similar size, the smaller is seen as further away © 2002 John Wiley & Sons, Inc.

Motion Perception n Visual system is wired to detect motion  Rods in retina are sensitive to motion  Neurons in visual cortex respond to motion n Two systems for processing movement:  A: eye is stationary as object moves  B: eye moves to maintain object at same place on the retina; muscle signals are used to infer movement © 2002 John Wiley & Sons, Inc.

Linear Perspective as a Depth Cue © 2002 John Wiley & Sons, Inc.

Perceptual Constancy n Color: Tendency to perceive object color as stable even under conditions of changing illumination n Shape: We recognize an object as having the same shape although we may view it in a different angle, at a different distance... n Size: Objects do not differ in size when viewed from different distances © 2002 John Wiley & Sons, Inc.

Copyright Copyright 2002 by John Wiley & Sons, Inc., New York, NY. All rights reserved. No part of the material protected by this copyright may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission of the copyright owner. © 2002 John Wiley & Sons, Inc.