Sensation and Perception Sensation is the process of

Sensation and Perception • Sensation is the process of receiving, converting, and transmitting information from the outside world. – Sensory organs contain receptors that transduce sensory energy into nerve impulses that are carried to the brain. • Top-down processing versus bottom-up processing © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Sensation/Perception • Transduction: sensory receptors convert a physical energy into nerve impulses © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Understanding Sensation: Processing Three Types of Processing: 1. Transduction: converts sensory stimuli into neural impulses that are sent on to the brain 2. Sensory Reduction: filters and analyzes incoming sensations before sending on to the brain 3. Coding: converts particular sensory input into a specific sensation sent to differing parts of the brain © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Sensory Thresholds • Psychophysics: testing limits and changes • Absolute Threshold: smallest amount of a stimulus we can detect • Difference Threshold: minimal difference needed to detect a a stimulus change; also called the just noticeable difference (JND) © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Signal Detection Theory © 2011 The Mc. Graw-Hill Companies, Inc.

Modification of Sensation • A key function of sensory systems is to detect change within the environment. – Movement in the peripheral aspects of the eye may signal food or danger. – Constant pressure of an object on the skin may not be important. • A stimulus that moves across the skin may be a snake or a spider. • The skin adapts to constant pressure. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Sensory Adaptation • Sensory adaptation refers to the fact that repeated or constant stimulation decreases the number of sensory messages sent to the brain, which causes decreased sensation. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Gate-Control Theory of Pain • Pain sensations are processed and altered by mechanisms within the spinal cord. – Endorphins relieve pain by inhibiting pain perception. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Vision • External light falls on receptors within the eye to generate the visual message. • Light = electromagnetic radiation – Wavelength of light determines color © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Physical/Perceptual properties of light © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Properties of Light – wavelength: distance between peaks • perceived as hue • some wavelengths beyond human sensation – amplitude: height of wave • perceived as brightness – purity: mixture of wavelengths • perceived as saturation © 2011 The Mc. Graw-Hill Companies, Inc.

Anatomy of the Eye © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Glaucoma: Open and Closed Angle © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Accommodation • Accommodation refers to automatic adjustments of the eye, which occurs when muscles change the shape of the lens so that it focuses light on the retina from objects at different distances. – Nearsightedness – Farsightedness © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Eye as optical instrument Light refraction © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Three layers of eye © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Structure of the Eye: Retina © 2011 The Mc. Graw-Hill Companies, Inc.

Structure of the Eye: Retina Rods – sensitive to even dim light, but not color – function well in low illumination – humans have ≈ 120 million rods Cones – respond to color – operate best under high illumination © 2011 The Mc. Graw-Hill Companies, Inc. – humans have ≈ 6 million cones

Retinal Photoreceptors • Light passes through the retinal layers to reach the photoreceptors at the inner retinal surface. • Photoreceptors and bipolar cells conduct potentials to the ganglion cells, which in turn initiate action potentials which are transmitted to the thalamus. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Visual System © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Color Perception • Humans are able to discriminate 7 million different hues. • Colors convey important information: – Ripeness of food – Danger signals • Trichromatic theory – Eye contains 3 different color sensitive elements • Blue, green or red elements • Trichromatic theory accounts for color mixing of lights. • Opponent-Process theory – Visual system is organized into red-green, blueyellow and black-white units. • Theory can account for negative color afterimages. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Sensory Coding • Activation of retinal cells by light results in action potentials that travel along neurons that project to the occipital cortex © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Properties of Sound Wavelength (distance between peaks) - determines frequency - perceived as pitch - some wavelengths cannot be perceived Amplitude (height of wave) - perceived as loudness Mixture of Wavelengths; Complex Sounds © 2011 The Mc. Graw-Hill Companies, Inc. - perceived as timbre / tone saturation

Sound Loudness (d. B) © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Anatomy of the Ear (Sound Waves) © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Crosssection of cochlea © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Theories of Hearing Place Theory of Pitch Perception – location of stimulation is important – only explains perception of high frequencies Frequency Theory of Pitch Perception – frequency of nerve firing • limitations of neuronal firing rate – volley principle • cell clusters can exceed limitations of firing © 2011 The Mc. Graw-Hill Companies, Inc. rate

Hearing Loss • Conduction deafness: Middle-ear deafness resulting from problems with transferring sound waves to the innerear. • Nerve Deafness: Inner-ear deafness resulting from damage to the cochlea, hair cells, or auditory nerve. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Olfaction • Receptors are embedded in a mucus-coated membrane called the olfactory epithelium. • When chemical molecules in the air pass through the nose, the receptors initiate a neural impulse which travels to the olfactory bulb, where most olfactory information is interpreted. • Lock-and-Key Theory: humans can smell various odors because each threedimensional odor molecule fits into only one type of receptor. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Gustation • Taste receptors are located on the tongue and are sensitive to five major tastes: salty, sweet, sour, bitter and umami. • Taste receptors respond differentially to the varying shapes of food and liquid molecules. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

The Body Senses • Skin Senses: there are three basic skin sensations: touch, temperature, and pain. • Vestibular Sense: sense of body orientation with respect to gravity and three-dimensional space – The semicircular canals provide the brain with balance information. • Kinesthetic Sense: sensory system for body posture, orientation and movement – Kinsethetic receptors are found throughout the muscles, joints, and tendons of the body. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Perception • Perceptual processes include: – Selection refers to choosing which of many stimuli that will be processed. – Organization involves collecting the information into some pattern. – Interpretation involves understanding the pattern. • Perceptions can be in error – Illusions are visual stimuli that are misinterpreted. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Horizontal-Vertical Illusion WHICH LINE IS LONGER? © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Selection • Selective attention: filtering out and attending only to important sensory messages. • Feature detectors: specialized cells in the brain that respond only to certain sensory information • Habituation: tendency of the brain to ignore environmental factors that remain constant © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Form Perception • Gestaltists proposed laws of organization that specify how people perceive form. • Figure and ground are basic organizational themes for perception. – Figure is perceived as distinct from the background. – Figure is closer to the viewer than the background. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Visual Perception: Depth Monocular Cues – Pictorial Cues • • • familiar size height in the field of view linear perspective overlap shading texture gradients © 2011 The Mc. Graw-Hill Companies, Inc.

Monocular Cues: Shading, Texture Gradient © 2011 The Mc. Graw-Hill Companies, Inc.

Monocular Cues: Linear Perspective, Height in Field © 2011 The Mc. Graw-Hill Companies, Inc.

Gestalt Organizational Principles © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Perceptual Constancies • Perceptual Constancy is the tendency for the environment to be perceived as remaining the same even with changes in sensory input. – Size constancy – Shape constancy – Color constancy – Brightness constancy © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Depth Perception • Depth perception is the ability to perceive three-dimensional space and to accurately judge distance. • Binocular cues include retinal disparity and convergence. • Monocular cues include linear perspective, interposition, relative size, texture gradient, aerial perspective, light and shadow, accommodation and motion parallax. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Interpretation • Interpretation is influenced by: perceptual adaptation perceptual set individual motivation frame of reference © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Subliminal Perception • Subliminal stimuli are stimuli presented below the threshold of awareness; the effect on behavior is uncertain. © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E

Extrasensory Perception • ESP refers to the ability to perceive stimuli that are outside the 5 senses – Telepathy: the ability to read minds – Clairvoyance: the ability to perceive objects or events – Precognition: the ability to predict the future – Psychokinesis: the ability to move objects © 2004 John Wiley & Sons, Inc. Huffman: PSYCHOLOGY IN ACTION, 7 E