Sensation & Perception Chapter 4 Sensation & Perception This multimedia product and its contents are protected under copyright law. The following are prohibited by law: Any public performance or display, including transmission of any image over a network; Preparation of any derivative work, including the extraction, in whole or in part, of any images Any rental, lease or lending of the program. ISBN: 0-131-73180-7 Copyright © Allyn and Bacon 2007

Sensation and Perception Sensation – An early stage of perception in which neurons in a receptor create an internal pattern of nerve impulses that represent the conditions that stimulated it – either inside or outside the body Perception – A process that makes sensory patterns meaningful and more elaborate Copyright © Allyn and Bacon 2006

How Does Stimulation Become Sensation? The brain senses the world indirectly because the sense organs convert stimulation into the language of the nervous system: neural impulses Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Transduction Transduction – Transformation of one form of energy into another – especially the transformation of stimulus information into nerve impulses Receptors – Specialized neurons that are activated by stimulation and transduce (convert) it into a nerve impulse Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Transduction Sensory pathway – Bundles of neurons that carry information from the sense organs to the brain Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Sensory Adaptation Sensory adaptation – Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Thresholds Absolute threshold – Amount of stimulation necessary for a stimulus to be detected Difference threshold – Smallest amount by which a stimulus can be changed and the difference be detected (also called just noticeable difference – JND) Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Thresholds Weber’s law – The JND is always large when the stimulus intensity is high, and small when the stimulus intensity is low Fechner’s law – S = k log R S = sensation R = stimulus k = constant that differs for each sensory modality Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Thresholds Steven’s power law – S = kla S = sensation k = constant l = stimulus intensity a = a power exponent that depends on the sense being measured Copyright © Allyn and Bacon 2006

Signal Detection Theory Signal detection theory – Perceptual judgment as combination of sensation and decision-making processes Stimulus event Neural activity Comparison with personal standard Action (or no action) Copyright © Allyn and Bacon 2006

Subliminal Persuasion Studies have found that subliminal words flashed briefly on a screen can “prime” a person’s later responses No controlled research has ever shown that subliminal messages delivered to a mass audience can influence people’s buying habits Copyright © Allyn and Bacon 2006

How Are the Senses Alike? How Are They Different? The senses all operate in much the same way, but each extracts different information and sends it to its own specialized processing region in the brain Copyright © Allyn and Bacon 2006

The Anatomy of Visual Sensation Retina – Light-sensitive layer at the back of the eyeball Photoreceptors – Light-sensitive cells in the retina that convert light energy to neural impulses Rods – Sensitive to dim light but not colors Cones – Sensitive to colors but not dim light Fovea – Area of sharpest vision in the retina Copyright © Allyn and Bacon 2006

The Anatomy of Visual Sensation Optic nerve – Bundle of neurons that carries visual information from the retina to the brain Blind spot – Point where the optic nerve exits the eye and where there are no photoreceptors Copyright © Allyn and Bacon 2006

The Anatomy of Visual Sensation Visual cortex – Part of the brain – the occipital cortex – where visual sensations are processed Color – Psychological sensation derived from the wavelength of visible light – color, itself, is not a property of the external world Copyright © Allyn and Bacon 2006

Transduction of Light in the Retina Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Afterimages Afterimages – Sensations that linger after the stimulus is removed In the following slide, fix your eyes on the dot in the center of the flag Copyright © Allyn and Bacon 2006

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Neural Pathways in the Human Visual System Copyright © Allyn and Bacon 2006

How the Visual System Creates Color Electromagnetic spectrum – Entire range of electromagnetic energy, including radio waves, X-rays, microwaves, and visible light Visible spectrum – Tiny part of the electromagnetic spectrum to which our eyes are sensitive Copyright © Allyn and Bacon 2006

How the Visual System Creates Color Color blindness – Vision disorder that prevents an individual from discriminating certain colors Brightness – Sensation caused by the intensity of light waves Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Color Blindness Copyright © Allyn and Bacon 2006

How the Visual System Creates Brightness Wavelength Intensity (amplitude) Color Brightness Copyright © Allyn and Bacon 2006

Hearing: If a Tree Falls in the Forest... The Physics of Sound Frequency – Number of cycles completed by a wave in a given amount of time Low Frequency High Frequency Copyright © Allyn and Bacon 2006

Hearing: If a Tree Falls in the Forest... The Physics of Sound Amplitude – Physical strength of a wave High Amplitude Low Amplitude Copyright © Allyn and Bacon 2006

How Sound Waves Become Auditory Sensations Tympanic membrane – The eardrum Copyright © Allyn and Bacon 2006

How Sound Waves Become Auditory Sensations Cochlea – Where sound waves are transduced Copyright © Allyn and Bacon 2006

How Sound Waves Become Auditory Sensations Basilar membrane – Thin strip of tissue sensitive to vibrations Cochlea Copyright © Allyn and Bacon 2006

How Sound Waves Become Auditory Sensations Auditory nerve – Neural pathway connecting the ear and the brain Copyright © Allyn and Bacon 2006

How Sound Waves Become Auditory Sensations Auditory cortex – Portion of the temporal lobe that processes sounds Copyright © Allyn and Bacon 2006

The Psychology of Pitch, Loudness, and Timbre Pitch – Sensory characteristic of sound produced by the frequency of the sound wave Loudness – Sensory characteristic of sound produced by the amplitude (intensity) of the sound wave Timbre – Quality of a sound wave that derives from the wave’s complexity Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Deafness Conduction deafness – An inability to hear resulting from damage to structures of the middle or inner ear Nerve deafness – An inability to hear, linked to a deficit in the body’s ability to transmit impulses from the cochlea to the brain, usually involving the auditory nerve or higher auditory processing centers Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Position and Movement Vestibular sense – Sense of body orientation with respect to gravity Kinesthetic sense – Sense of body position and movement of body parts relative to each other Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Smell Olfaction – Sense of smell Olfactory bulbs – Brain sites of olfactory processing Pheromones – Chemical signals released by organisms to communicate with other members of the species Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Smell Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Taste Gustation – The sense of taste Taste buds – Receptors for taste (primarily on the upper side of the tongue) Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 The Skin Senses Touch Warmth Cold Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Pain Placebos – Substances that appear to be drugs but are not Placebo effect – A response to a placebo caused by subjects’ belief that they are taking real drugs Copyright © Allyn and Bacon 2006

What is the Relationship Between Perception and Sensation? Perception brings meaning to sensation, so perception produces an interpretation of the external world, not a perfect representation of it Copyright © Allyn and Bacon 2006

What is the Relationship Between Perception and Sensation? Percept – Meaningful product of a perception Copyright © Allyn and Bacon 2006

The Machinery of Perceptual Processing Feature detectors – Cells in the cortex that specialize in extracting certain features of a stimulus Binding problem – A major unsolved mystery in cognitive psychology, concerning the physical processes used by the brain to combine many aspects of sensation to a single percept Copyright © Allyn and Bacon 2006

Bottom-Up and Top-Down Processing Bottom-up processing – Analysis that emphasizes characteristics of the stimulus, rather than internal concepts Top-down processing – Emphasizes perceiver's expectations, memories, and other cognitive factors Copyright © Allyn and Bacon 2006

Perceptual Constancies Perceptual constancy – Ability to recognize the same object under different conditions, such as changes in illumination, distance, or location Copyright © Allyn and Bacon 2006

Perceptual Ambiguity and Distortion Illusions – Demonstrably incorrect experience of a stimulus pattern, shared by others in the same perceptual environment Ambiguous figures – Images that are capable of more than one interpretation Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Perceptual Illusions Do you see or ? Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Perceptual Illusions The Herman Grid Do you see small gray squares between the black squares? Copyright © Allyn and Bacon 2006

Theoretical Explanations for Perception Learning-based inference – View that perception is primarily shaped by learning, rather than innate factors Perceptual set – Readiness to detect a particular stimulus in a given context Copyright © Allyn and Bacon 2006

Cultural Influences on Perception B Which box is bigger, A or B? Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 The Gestalt Approach Gestalt psychology – View that much of perception is shaped by innate factors built into the brain Figure – Part of a pattern that commands attention Ground – Part of a pattern that does not command attention; the background Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 The Gestalt Approach Subjective contours – Boundaries that are perceived but do not appear in the stimulus pattern Closure – Tendency to fill in gaps in figures and see incomplete figures as complete Copyright © Allyn and Bacon 2006

The Gestalt Laws of Perceptual Grouping Similarity Proximity Continuity Common fate Prägnanz Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2006 Law of Prägnanz A BIRD IN THE THE HAND Copyright © Allyn and Bacon 2006

Copyright © Allyn and Bacon 2007 End of Chapter 4 Copyright © Allyn and Bacon 2007