Sensation & Perception Chapter 4 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 • Sensory pathway: Bundles of neurons that carry information from the sense organs to the brain Sensation and Perception • Sensation: Neurons in a receptor create an internal pattern of nerve impulses that represent the conditions that stimulated it • Perception: A process that makes sensory patterns meaningful and more elaborate • Stimulation Transduction Sensation Perception Sensory Adaptation • Sensory adaptation: Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while • Examples??? Thresholds • Absolute threshold: Amount of stimulation necessary for a stimulus to be detected (50% of time) • Difference threshold: Smallest amount by which a stimulus can be changed and the difference be detected (also called just noticeable difference – JND) Looking at the JND • Weber’s law: The JND increases with the magnitude of the stimulus. – The JND is large when the stimulus intensity is high, and small when the stimulus intensity is low • TV (volume high – turn down a lot, volume low – turn down little) • Groceries (50 pound bag – need to add more than you would to a 25 pound bag) • Steven’s power law: – Used for wider array of stimuli (shock, temperature) – Fills in gaps left by Weber and Fechner Signal Detection Theory • Signal detection theory: Perceptual judgment as combination of sensation and decision-making processes – Based on each individual’s sensitivity and response criterion – Example: holiday weekend on the interstate • • • • False Alarm (brakes and no cop) Hit (brakes and cop) Miss (no brakes and cop) Correct Rejection (no brakes and no cop) – Lowers response criterion and raises hit rates • Flawed merchandise off the assembly line • TSA putting weapons in bags Subliminal Persuasion • Studies have found that stimuli flashed subliminally on a screen can “prime” a person’s later responses. • No controlled research has ever shown that subliminal messages delivered to a mass audience influences buying habits. – Subtle, fleeting effect on thinking – No powerful, enduring effect on behavior The Anatomy of Visual Sensation Retina: Light-sensitive layer at the back of the eyeball – transduction occurs here! • 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 • http://www.youtube.com/watch?v=x6Ua5d3wlA0 (6:32) Fovea: Area of sharpest vision in the retina The Anatomy of Visual Sensation • Optic nerve: Bundle of neurons that carries visual information from the retina to the brain • Rods/conesbipolar cellsganglion cells Blind spot: Point where the optic nerve exits the eye and where there are no photoreceptors (money in the bank demo) Color Blindness & Afterimages • Color blindness: Vision disorder that prevents an individual from discriminating certain colors – Red-green is most common! • Afterimages: Sensations that linger after the stimulus is removed • Fix your eyes on the center for a negative afterimage… How the Visual System Creates Color • Visual cortex: Part of the brain – the occipital cortex – where visual sensations are processed • Brightness: Sensation caused by the intensity of light waves • Color: Psychological sensation derived from the wavelength of visible light – color, itself, is not a property of the external world • 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 How the Visual System Creates Brightness Wavelength Intensity (amplitude) Color Brightness Sensing Colors • Trichromatic Theory: Idea that colors are sensed by three different types of cones sensitive to light in the red, blue and green wavelengths. – Explains the earliest stage of color sensation. • Opponent-process Theory: Idea that cells in the visual system process colors in complimentary pairs, such as red or green or as yellow blue. – Explains color sensation from the bipolar cells onward in the visual system. Hearing: How Sound Waves Become Auditory Sensations Pinna Ear Canal Tympanic Membrane Middle Ear Oval Window Cochlea (Basilar Membrane) Auditory Nerve Tympanic membrane: The eardrum Hearing: How Sound Waves Become Auditory Sensations Cochlea: Where sound waves are transduced Hearing: How Sound Waves Become Auditory Sensations Cochlea Basilar membrane: Thin strip of tissue with hairs sensitive to vibrations Hearing: How Sound Waves Become Auditory Sensations Auditory nerve: Neural pathway connecting the ear and the brain Deafness • Conduction deafness: Results from damage to structures of the middle or inner ear • Nerve deafness: Linked to a deficit in the body’s ability to transmit impulses from the cochlea to the brain – Usually involves the auditory nerve or higher auditory processing centers Hearing: The Physics of Sound • Loudness: produced by the amplitude of a sound wave - Amplitude: Physical strength of a wave High Amplitude Low Amplitude Hearing: The Physics of Sound • Pitch: produced by the frequency of a sound wave – Frequency: Number of cycles completed by a wave in a given amount of time Low Frequency High Frequency How Sound Waves Become Auditory Sensations • Pitch: – Place Theory: different places on the basilar membrane send neural codes for different pitches – Frequency Theory: neurons have different firing rates for different sound wave frequencies • Timbre: Quality of a sound wave that derives from the wave’s complexity • Auditory cortex: Portion of the temporal lobe that processes sounds Position and Movement • Vestibular sense: Sense of body orientation with respect to gravity • http://www.youtube.com/watch?v=x6Ua5d3wlA0 (7:21) • Kinesthetic sense: Sense of body position and movement of body parts relative to each other 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 Smell Taste • Gustation: The sense of taste Taste buds: Receptors for taste (primarily on the upper side of the tongue) The Skin Senses and Pain • Gate-control Theory: An explanation for pain control that proposes we have a neural “gate” that can, under some circumstances, block incoming pain signals. • 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 The Machinery of Perceptual Processing • Percept: Meaningful product of a perception • 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 Bottom-Up and Top-Down Processing • Bottom-up processing: Analysis that begins with the sense receptors and works up to the brain’s integration of sensory information • http://www.youtube.com/watch?v=x6Ua5d3wlA0 (50) • Top-down processing: Analysis guided by higher-level mental processes - emphasizes perceiver's expectations, memories, and other cognitive factors • http://www.youtube.com/watch?v=x6Ua5d3wlA0 (1:44) Perceptual Constancies • Perceptual constancy: Ability to recognize the same object under different conditions, such as changes in illumination, distance, or location • Shape, color, size Perceptual Illusions Do you see or ? Perceptual Ambiguity and Distortion • Illusions: Distortion of a stimulus pattern, shared by others in the same perceptual environment – More likely when: • stimulus is unclear • info is missing • elements combined in unusual ways • familiar patterns aren’t apparent • Ambiguous figures: Images that are capable of more than one interpretation The Gestalt Approach • Gestalt psychology: View that much of perception is shaped by innate factors built into the brain (nature) – The whole pattern is greater than the sum of its parts. • Figure: Part of a pattern that commands attention • Ground: Part of a pattern that does not command attention; the background 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 The Gestalt Laws of Perceptual Grouping Proximity Similarity Closure Continuity Common Fate Prägnanz Binocular Cues – two eye depth cues • Binocular Convergence: lines of vision from each eye converge at different angles on objects at different distances – Can feel eye muscles change as you focus at different distances • Retinal Disparity: difference in perspectives of the 2 eyes (greater disparity for nearby objects – provides us with depth information) Monocular Cues – one eye depth cues • Monocular Cues: – Linear Perspective: parallel lines appear to meet in the distance Monocular Cues – one eye depth cues • Monocular Cues: – Relative Motion: objects closer to you move faster than those further away from you Monocular Cues – one eye depth cues • Monocular Cues: – Relative Size: 2 objects the same size; the one that appears larger = closer to us Monocular Cues – one eye depth cues • Monocular Cues: – Interposition: hidden objects are more distant than those objects that hide them Monocular Cues – one eye depth cues • Monocular Cues: – Texture Gradient: as object gets further away from us, the texture gets smoother Theoretical Explanations for Perception • Learning-based inference: View that perception is primarily shaped by learning, rather than innate factors (nurture); opposite of Gestalt • What determines how successful we will be in forming an accurate percept? – Context, expectation, perceptual set – each influenced by culture – Perceptual set: Readiness to detect a particular stimulus in a given context Cultural Influences on Perception A B Which box is bigger, A or B? Muller-Lyer Illusion • When 2 objects make the same size image on the retina, and we judge one to be farther away than the other, we assume that the more distant one is larger.