Sensation & PerceptionChapter 5

Sensing & Perceiving Information Sensation: Receiving

Perception: Organizing & Interpreting

Vision – The Eye Light enters eye through the cornea Passes through the pupil and lens Focused into an image on the retina Retina

Light sensitive inner surface of the eye Contains Rods & Cones Receptor cells convert light to neural impulses and

send to brain Brain reassembles impulses into an image

Vision – The Eye

Vision – Retina Receptors Rods

detect black, white, and gray necessary for peripheral and twilight vision

Cones concentrated near the center of retina function in daylight or well-lit conditions detect fine detail color vision

Vision--Receptors

Receptors in the Human Eye

Cones Rods

Number

Location in retina

Sensitivity in dim light

Color sensitive? Yes

Low

Center

6 million

No

High

Periphery

120 million

The Eye

Optic Nerve: nerve that carries neural impulses from the eye to the brain

Blind Spot: point at which the optic nerve leaves the eye No receptor cells creates a “blind spot”

Vision – Feature Detection

Feature Detectors nerve cells that respond to specific features

of a stimulus shape, angle, or movement

fMRI can be used to determine what object a person is looking at

Visual Information Processing

Parallel Processing processing many parts of a problem all at

once the brain’s natural mode of information

processing for many functions (including vision)

Visual Information Processing

Scene

Retinal processing:Receptor rods andconesbipolar cells

ganglion cells

Feature detection:Brain’s detector cells

respond to elementaryfeatures-bars, edges, or

gradients of light

Abstraction:Brain’s higher-level cells

respond to combinedinformation from

feature-detector cells

Recognition:Brain matches the

constructed image withstored images

Color-Deficient Vision

People who suffer red-green blindness have trouble perceiving the number within the design

Color Vision

Young-Helmholtz trichromatic (three-color) theory retina has 3 different color receptors (red, green,

blue) different combinations allow for the perception of

any color Opponent-process theory

opposing processes of retina enable color vision e.g., some neurons are turned on by red and off

by green

Audition Audition- the sense of hearing Frequency- the number of complete

wavelengths that pass a point in a given time Pitch- a tone’s highness or lowness

depends on frequency long sound waves = low frequency & low pitch short sound waves = high frequency & high pitch

Audition--The Ear Sound waves

auditory canal eardrum (vibrates with the waves) middle ear cochlea (in inner ear) triggers neural impulses (auditory nerve) thalamus auditory cortex (temporal lobe)

Middle Ear chamber between the eardrum and cochlea contains 3 tiny bones (hammer, anvil, stirrup)

that transmit vibrations to the cochlea

Audition--The Ear

Inner Ear innermost part of ear Contains the Cochlea

a fluid-filled tube through which sound waves trigger nerve impulses

Decibel Levels - Common Sounds

Locating Sounds sound reaches one

ear more intensely and more quickly

auditory system is able to detect tiny differences

hearing loss in one ear = difficulty locating sounds

Touch Skin Sensations

pressure only skin sensation with identifiable

receptors warmth cold pain Rubber hand illusion

http://www.youtube.com/watch?v=TCQbygjG0RU

Pain No theory explains all available findings Gate-Control Theory (1960s)

provides a useful model for understanding pain the spinal cord contains small fibers (conduct pain

signals) and large fibers (conduct other sensory signals)

“gate” opened by the activity of pain signals traveling up small nerve fibers

“gate” closed by activity in larger fibers or by information coming from the brain

Pain Control

Massaging area next to pain Distraction

Diverting the brain’s attention may bring relief Pleasant imagery Count backward Virtual reality

Taste Taste Sensations

sweet sour salty bitter savory (umami)

Taste

Taste receptors reproduce themselves every 2 weeks taste sensitivity and # of taste buds decrease as

we age Sensory Interaction

one sense may influence another sense the smell of food influences its taste smell + texture = flavor rubber hand illusion (vision & touch interact)

Smell

humans can detect 10,000 odors olfactory receptor cells

respond to aromas messages sent through receptor axons to the

olfactory bulb in the brain messages then travel from olfactory bulb to

temporal lobe & limbic system odors can evoke memories

Smell

Body Position and Movement

Sixth sense Kinesthesis

the system for sensing the position and movement of individual body parts

interacts with vision Vestibular sense

monitors head and body position to maintain balance

fluid in the inner ear moves when head moves messages are sent to the cerebellum

Perceptual Organization- organizing & interpreting info from senses

Gestalt an organized whole tendency to

integrate pieces of information into meaningful wholes

Necker cube

Perceptual Organization First: Need to

discriminate objects from backgrounds

Figure and Ground perceiving an object (figure) as distinct from its surroundings (ground)

In a busy restaurant: voice you attend to = figure all other voices = ground

Perceptual Organization- Gestalt Next step: Need to organize the figure into a

meaningful form Grouping

the tendency to organize stimuli into meaningful groups

grouping rules identified by Gestalt psychologists the “whole” that we perceive differs from the sum

of its parts

Perceptual Organization- Gestalt Grouping Rules

proximity - we group nearby figures together similarity - we group similar figures together continuity – we perceive continuous patterns closure – we fill in gaps to create complete objects connectedness - spots, lines, and areas are seen

as a unit when connected

Perceptual Organization- Gestalt

Proximity Similarity

Continuity Closure Connectedness

Perceptual Organization-Depth Perception

Visual Cliff

Perceptual Organization

Depth Perception seeing objects in three dimensions allows us to estimate distance

Visual Cliff laboratory technique used to test depth

perception http://www.youtube.com/watch?v=eyxMq11xWzM

Perceptual OrganizationDepth Perception

Binocular cues – depth cues depend on use of two eyes retinal disparity

images from the two eyes differ brain compares the images to compute

distance the larger the difference, the closer the object

Perceptual OrganizationDepth Perception

Monocular Cues depth cues needed for objects at further distances available to each eye separately

relative height higher objects seen as more distant

relative size smaller image is more distant

Depth Perception

Monocular Cues (continued) interposition

if one object blocks our view of another, we perceive that object to be closer

Depth Perception

Monocular Cues (continued) relative clarity

hazy object seen as more distant relative motion

as we move, stable objects appear to also move fix gaze on object: those beyond appear to move

with you; those in front appear to move backward relative brightness

dimmer objects seem farther away

Depth Perception

Monocular Cues (continued) linear perspective

parallel lines appear to converge with distance

Perceptual Constancy perceiving objects as

unchanging despite changes in illumination and retinal image able to recognize objects despite

changes in color, shape, & size

Shape Constancy

Shape constancy – as a door opens the shape projected on retina looks more like a trapezoid…but we still perceive it as rectangular.

Perceptual Constancy

Color depends on context Color Constancy

we perceive familiar objects as having consistent color even if illumination changes and alters the

wavelengths reflected by the object

Perceptual OrganizationSize-Distance Relationship

Perceptual Organization- Size-Distance Relationship

Depth Perception

Perceptual OrganizationMüller-Lyer Illusion

Perceptual OrganizationBrightness Contrast

Perceptual Interpretation Perceptual Adaptation

(vision) ability to adjust to an artificially displaced visual field glasses that invert view of the world (looks

upside down) humans can adapt relatively quickly and learn

to coordinate movements accurately

Perceptual Interpretation

Perceptual Set a mental predisposition to perceive

one thing and not another our experiences and expectations

influence what we perceive

Perceptual Set – context effect

Is There Extrasensory Perception?

Parapsychology the study of paranormal phenomena

Astrological predictions Psychic healing ESP Psychokinesis (“mind over matter”; levitating)

Is There ESP?

Extrasensory Perception (ESP) controversial claim that perception can occur

apart from sensory input types of ESP:

Telepathy (mind-to-mind communication) Clairvoyance (sensing remote events) Precognition (perceiving future events)