Ch 3 sensation perception

Copyright McGraw-Hill, Inc. 20101

Chapter 3Sensation and Perception


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How We Sense and Perceive the World

The Visual System

The Auditory System

Other Senses


Sensation and Perception

Sensation Process of receiving stimulus energies from

external environment

Perception Process of organizing and interpreting sensory

information


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


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


The Human Senses


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


‘Confused’ Senses

Synaesthesia One sense induces experience in another sense

Phantom Limb Pain Reported pain in amputated arm or leg


Thresholds

Absolute Threshold Minimum amount of detectable stimulus energy


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


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


Signal Detection Theory


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


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


The Visual Stimulus

Light Form of electromagnetic energy

Wavelength Hue, or color

Amplitude Brightness

Purity Saturation, or richness


Wavelengths & Color


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



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




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


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


Structure of the Eye: Retina


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


Visual Processing


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


Color Vision: Trichromatic Theory

Three types of cones, sensitive to different (but overlapping) ranges of wavelength

Support includes . . . Color matching

Color blindness


Color Blindness


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.


Negative Afterimage


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.’


Figure-Ground Relationship


Gestalt Psychology


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


Monocular Cues: Linear Perspective


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


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


Perceiving Constancy

Size constancy

Shape constancy


The Nature of Sound

Sound Vibrations in air processed by auditory system

Wavelength Frequency Pitch

Amplitude Pressure Loudness

Complexity Saturation Timbre


The Nature of Sound


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


Structure of the Ear


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.


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.


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


Other Senses

Skin (Cutaneous) Touch Temperature Pain

Chemical Smell Taste

Kinesthetic Vestibular


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)


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


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


Chemical Senses: Taste


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


Chemical Senses: Smell


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

Ch 3 sensation perception

Documents

color perception

visual stimuli

sensory information

sensation perception

processing information

shape of eye

stimulus information

eye pupil