Copyright McGraw-Hill, Inc Chapter 3 Sensation and Perception

Copyright McGraw-Hill, Inc Chapter Preview How We Sense and Perceive the World The Visual System The Auditory System Other Senses

Copyright McGraw-Hill, Inc Sensation and Perception Sensation Process of receiving stimulus energies from external environment Perception Process of organizing and interpreting sensory information

Copyright McGraw-Hill, Inc Sensation & Perception: Processes Bottom-Up Processing Information about external environment  Sensory receptors  Brain Making sense of information Top-Down Processing Starts with cognitive processing at higher levels of brain

Copyright McGraw-Hill, Inc Sensory Receptors and the Brain Sensory Receptors Specialized cells that detect stimulus information and transmit it to sensory (afferent) nerves and brain Afferent nerves Bring information to brain Efferent nerves Send messages away from brain to body

Copyright McGraw-Hill, Inc The Human Senses

Copyright McGraw-Hill, Inc Sensation Photoreception Detection of light Perceived as sight Mechanoreception Detection of pressure, vibration, and movement Perceived as touch, hearing, and equilibrium Chemoreception Detection of chemical stimuli Perceived as smell and taste

Copyright McGraw-Hill, Inc ‘Confused’ Senses Synaesthesia One sense induces experience in another sense Phantom Limb Pain Reported pain in amputated arm or leg

Copyright McGraw-Hill, Inc Thresholds Absolute Threshold Minimum amount of detectable stimulus energy

Copyright McGraw-Hill, Inc Thresholds Subliminal Perception Detection of information below level of conscious awareness Difference Threshold (Just Noticeable Difference) Degree of difference that must exist between two stimuli before difference is detected Weber’s Law Principle that two stimuli must differ by a constant minimum percentage to be perceived as different

Copyright McGraw-Hill, Inc Signal Detection Theory Theory of perception which focuses on decision- making about stimuli in presence of uncertainty Information acquisition Criterion Possible outcomes: Hit Miss False alarm Correct rejection

Copyright McGraw-Hill, Inc Signal Detection Theory

Copyright McGraw-Hill, Inc Perception of Sensory Stimuli Attention Selective Cocktail party effect Shiftable Novelty, size, color, movement Stroop effect Perceptual Set Predisposition or readiness to perceive something a particular way

Copyright McGraw-Hill, Inc Other Perceptual Phenomena Sensory Adaptation Change in responsiveness of sensory system based on average level of surrounding stimulation Extrasensory Perception (ESP) Perception in absence of concrete sensory input Parapsychology Scientific study of ESP Absence of empirical data for existence of ESP

Copyright McGraw-Hill, Inc The Visual Stimulus Light Form of electromagnetic energy Wavelength  Hue, or color Amplitude  Brightness Purity  Saturation, or richness

Copyright McGraw-Hill, Inc Wavelengths & Color

Copyright McGraw-Hill, Inc Structure of the Eye Sclera White, outer part of eye Helps maintain shape of eye Protects eye from injury Iris Colored part of eye Pupil Opening in center of iris Size controlled by muscles in iris

Copyright McGraw-Hill, Inc Structure of the Eye Cornea Clear membrane just in front of eye Lens Transparent, somewhat flexible, disk-like structure The cornea and the lens both bend light falling on the surface of the eye just enough to focus it on the retina. Retina Multilayered, light-sensitive surface at back of eye Converts visual stimuli to neural impulses

Copyright McGraw-Hill, Inc Structure of the Eye

Copyright McGraw-Hill, Inc Visual Receptor Cells Cells on retina which convert electromagnetic energy into electrochemical impulses Rods Sensitive to light Not very useful for color vision Function well under low illumination Cones Used for color perception Require more light than rods

Copyright McGraw-Hill, Inc Structure of the Eye: Retina Fovea Tiny area in center of retina at which vision is best Contains only cones Rods & cones  Bipolar cells  Ganglion cells  Optic nerve Blind spot Place on retina containing neither rods nor cones Where optic nerve leaves eye

Copyright McGraw-Hill, Inc Structure of the Eye: Retina

Copyright McGraw-Hill, Inc Visual Processing Optic Nerve  Optic Chiasm  Visual Cortex Optic nerve fibers divide at optic chiasm: Left Visual Field  Right Hemisphere Right Visual Field  Left Hemisphere

Copyright McGraw-Hill, Inc Visual Processing

Copyright McGraw-Hill, Inc Visual Processing Feature Detectors Neurons in primary visual cortex that respond to particular features of a stimulus Parallel Processing Simultaneous distribution of information across different neural pathways Binding Integration of what is processed by different pathways or cells

Copyright McGraw-Hill, Inc Color Vision: Trichromatic Theory Three types of cones, sensitive to different (but overlapping) ranges of wavelength Support includes... Color matching Color blindness

Copyright McGraw-Hill, Inc Color Blindness

Copyright McGraw-Hill, Inc Color Vision: Opponent-Process Theory Afterimages Sensations that remain after stimulus is removed Not explained by trichromatic theory Explained by opponent-process theory Visual system treats colors as complementary pairs. Conclusion: Both theories are correct.

Copyright McGraw-Hill, Inc Negative Afterimage

Copyright McGraw-Hill, Inc Perceiving Shape Contour Location at which sudden change of brightness occurs Figure-Ground Relationship Principle by which perceptual field is organized into stimuli that stand out (figure) and those left over (ground) Gestalt Psychology School of thought interested in how people naturally organize perception according to certain patterns ‘Whole is different from sum of its parts.’

Copyright McGraw-Hill, Inc Figure-Ground Relationship

Copyright McGraw-Hill, Inc Gestalt Psychology

Copyright McGraw-Hill, Inc Perceiving Depth Ability to perceive objects three-dimensionally Binocular Cues  combined images from two eyes Disparity Convergence Monocular Cues  available from image in one eye Familiar size Height in field of view Linear perspective and relative size Overlap Shading Texture gradient

Copyright McGraw-Hill, Inc Monocular Cues: Linear Perspective

Copyright McGraw-Hill, Inc Perceiving Motion Retinas of humans cannot detect movement. Neurons specialized to detect motion Feedback from body Environment rich in cues Real movement Apparent movement Perception of stationary object as moving

Copyright McGraw-Hill, Inc Perceiving Constancy Recognition that objects are constant even though sensory input is changing Size constancy Same size despite retinal image changes Shape constancy Same shape despite orientation changes Color constancy Same color despite light changes

Copyright McGraw-Hill, Inc Perceiving Constancy Size constancy Shape constancy

Copyright McGraw-Hill, Inc The Nature of Sound Sound Vibrations in air processed by auditory system Wavelength  Frequency  Pitch Amplitude  Pressure  Loudness Complexity  Saturation  Timbre

Copyright McGraw-Hill, Inc The Nature of Sound

Copyright McGraw-Hill, Inc Structure of the Ear Outer Ear  Collects and channels sound Pinna External Auditory Canal Middle Ear  Channels sound to inner ear Eardrum Hammer, Anvil, & Stirrup Inner Ear  Converts sound into neural impulses Oval Window Cochlea Basilar Membrane  Hair Cells  Tectorial Membrane

Copyright McGraw-Hill, Inc Structure of the Ear

Copyright McGraw-Hill, Inc Theories of Hearing Place Theory Each frequency produces vibrations at a particular spot. But... explains high-frequency, not low-frequency, sounds Frequency Theory Perception of frequency depends on how often auditory nerve fires. But... single neurons have maximum firing rates Volley Principle Modification of frequency theory Clusters of nerve cells can fire neural impulses in rapid succession.

Copyright McGraw-Hill, Inc Auditory Processing Inner Ear  Auditory Nerve  Temporal Lobe Most fibers cross over midline between hemispheres: Left Ear  Right Hemisphere Right Ear  Left Hemisphere Some fibers go directly to same-side hemisphere.

Copyright McGraw-Hill, Inc Localizing Sound Each ear receives somewhat different stimuli. Distance  Timing Sound Shadow  Intensity Echolocation System based on returning echoes of sounds Used by bats; humans less accurate

Copyright McGraw-Hill, Inc Other Senses Skin (Cutaneous) Touch Temperature Pain Chemical Smell Taste Kinesthetic Vestibular

Copyright McGraw-Hill, Inc The Skin (Cutaneous) Senses Touch Mechanical energy, or pressure, against skin Temperature Warm and cold sensory nerve endings, or thermoreceptors Pain Widely-dispersed receptors with much higher thresholds for different types of physical stimuli (e.g., pressure, heat)

Copyright McGraw-Hill, Inc Pain Prostaglandins Stimulate pain receptors and cause experience of pain Neural pathways to brain Fast Pathway  Directly to thalamus Slow Pathway  Through limbic system Endorphins Neurotransmitters involved in turning pain signals on/off

Copyright McGraw-Hill, Inc Chemical Senses: Taste Detecting chemicals dissolved in saliva Papillae Bumps on surface of tongue Contain taste buds, receptors for taste Four taste qualities: sweet, sour, bitter, salty Taste fibers respond to range of chemicals spanning multiple taste elements Umami

Copyright McGraw-Hill, Inc Chemical Senses: Taste

Copyright McGraw-Hill, Inc Chemical Senses: Smell Detecting airborne chemicals Olfactory epithelium Lines roof of nasal cavity Contains sheet of receptor cells Neural pathway Olfactory areas of temporal lobe  Limbic system Superhighway to emotion & memory Interpersonal attraction & MHC genes

Copyright McGraw-Hill, Inc Chemical Senses: Smell

Copyright McGraw-Hill, Inc Kinesthetic and Vestibular Senses Kinesthetic Sense Information about movement, posture, orientation Vestibular Sense Information about balance, movement Proprioceptive Feedback Information about relative position of limbs and body Semicircular Canals Contain sensory receptors to detect head motion