Introduction to Psychology Sensation and Perception Perception • Aoccdrinig to a rscheearch sudty at Cmabrigde Uinervtisy, it deosn’t mttaer in what oredr the ltteers in a word are; the olny iprmoetnt tihng is that the frist and lsat ltteer be at the rghit pclae. The rset can be a toatls mses and you can sitll, raed it wouthit mcuh porblem. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Psychophysics • Sensation is the stimulation of sense organs • Perception is the selection, organization, and interpretation of sensory input. Thresholds • Sensory receptors are tuned to a particular form of energy – Auditory receptors in the ear code for sound pressure changes, not for light • 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. The Visual System • 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?) • 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. Transduction of Light • 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. Visual Pathways in Brain: “Where” versus “What” © 2002 John Wiley & Sons, Inc. Perception of Color • 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. Color Vision Theories • Young-Helmholtz: – Color is explained by differential activation of 3 color elements in eye • Could not account for negative color afterimages • 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. Sound • Sound waves are vibrations of molecules that travel through air. • Amplitude - decibels • Wavelength - frequency (cps or hertz) • Purity - timbre The Auditory System • External ear – pinna, eardrum • Middle ear – ossicles (hammer, anvil, stirrup) • Inner ear – cochlea • basilar membrane –hair cells Taste: the Gustatory System • • • • Taste buds Primary tastes: sweet, sour, bitter, salty Perception of flavor Papillae: circumvallate, foliate, & fungiform Smell: the Olfactory System • Smell: chemical substances dissolved in mucus • Olfactory cilia • Olfactory nerves • Olfactory bulb Skin Senses • Receptors are localized within the skin to detect physical stimuli in the outside world • 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. Pain • Pain is a source of information that relates to tissue destruction – Force – Heat – Chemical • Pain is a adaptive to a degree (motivates behaviors to terminate the source of the pain) • Pain is influenced by – – – – Cultural beliefs Emotional states Exogenous drugs (opiates) Internal transmitters (endorphins) © 2002 John Wiley & Sons, Inc.