Chapter 4:Sensation & Perception

“All knowledge has its origins in our perceptions.” – Leonardo Da Vinci

VisionHearingSmellTasteTouch

Definitions Sensation process of detecting, converting, and

transmitting raw sensory information from the external and internal environments to the brain (transduction)

Perception process of selecting, organizing and

interpreting sensory information enables us to recognize meaningful objects

and events

Sense organs: eyes, ears,

nose, tongue, skin,

& internal body organs

Happens in the brain!

ProcessingBottom-Up (parts to whole) Information processing beginning “at

the bottom” with raw sensory data that are sent “up” to the brain for higher level analysis

Data driven processing that moves from the parts to the whole

Top-Down (whole to parts) Information processing starting “at

the top” with higher level cognitive processes (such as expectations and knowledge) and then “working down”

Conceptually driven processing that moves from the whole to the parts

Ex: you have ingredients and must put them

together to make

something edible

Ex: you have ingredients

and a recipe & picture of a

completed cake and you must recreate

the cake

Top-Down Processing example

Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

Top down/ bottom up

Guitar player or old people

Fruit or face

Sensation- ThresholdsAbsolute Threshold minimum stimulation needed to

detect a particular stimulus usually defined as the stimulus

needed for detection 50% of the time

Difference Threshold minimum difference between two

stimuli that a subject can detect 50% of the time

just noticeable difference (JND) increases with magnitude

Ex: listen to headphones and indicate the earliest you hear a

tone

Ex: listen to headphones and indicate

when you hear a

change in volume of

soundEasier to tell the difference between 100 & 101Hz than 1000 & 1001Hz

Sensation- Thresholds

When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”.

0

25

50

75

100

Low Absolutethreshold

Medium

Intensity of stimulus

Percentageof correctdetections

Subliminal stimuli

Sensation- ThresholdsWeber’s Law- to perceive a difference between two stimuli, they must differ by a constant proportion light intensity- 8% weight- 2% tone frequency- 0.3%

Sensory Adaptation: diminished sensitivity with constant stimulation

- receptors higher up in sensory system get tired and fire less frequently

Apply it! Come up

with 3 examples

Sensation- Thresholds

Signal Detection Theory predicts how and when we detect the presence of

a faint stimulus (signal) amid background stimulation (noise)

assumes that there is no single absolute threshold High expectations- false positives Low expectations- false negatives detection depends partly on person’s

-experience -motivation-expectations -level of fatigue

Vision: Physical Properties of Waves

Short wavelength=high frequency(bluish colors, high-pitched sounds)

Long wavelength=low frequency(reddish colors, low-pitched sounds)

Great amplitude(bright colors, loud sounds)

Small amplitude(dull colors, soft sounds)

Perception of light and soundTransduction: conversion of one form of energy to anotherWavelength: Hue (color) and pitchAmplitude: brightness and loudnessPurity of wavelength: saturation of color and timbre for sound

Vision: Spectrum of

Electromagnetic Energy

Vision: Parts of the EyeCornea: transparent covering on the front of the eye Fovea: central point of focus on the back of the eyePupil: adjustable opening in the center of the eyeIris: a ring of muscle the forms the colored portion of the eye around the pupil and controls the size of the pupil openingLens: transparent structure behind pupil that changes shape to focus images on the retina

Accommodation: change in shape of lens focus near objects Retina Layers of neurons on inner surface of eye light sensitive contains rods and cones beginning of visual information processingBlind Spot: area of retina where optic nerve leaves back of

eye

Vision: Parts of the Eye

Retina’s Reaction to Light Receptors

Cones near center of retina

(fovea) fine detail and color vision daylight or well-lit

conditions

Receptors in the Human Eye

Cones RodsNumber

Location in retina

Sensitivity in dim light

Color sensitive? Yes

Low

Center

6 million

No

High

Periphery

120 million

Rods• Located in periphery of retina • detect black, white and gray• twilight or low light

Pathways from the Eyes to the Visual Cortex

Vision Acuity: the sharpness of vision Nearsightedness

nearby objects seen more clearly lens focuses image of distant objects in front of

retina Farsightedness

faraway objects seen more clearly lens focuses near objects behind retina

Farsighted Nearsighted Normal Vision Vision Vision

Color-Deficient Vision

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

Visual Information ProcessingTrichromatic (three color) Theory Young and Helmholtz The eye contains three different types

of cones capable of responding to various wavelengths of light red green blue

Visual Information Processing

Opponent-Process Theory: opposing retinal processes enable color vision

“ON” “OFF”red greengreen red blue yellow yellow blue black whitewhite black

The 2 Theories

Visual Perception: Gestalt- the whole is greater than the

sum of its parts

Gestalt Principles (gestalt = an organized whole. We tend to integrate pieces of info. into meaningful wholes)

Proximity Simplicity (law of good

form) Connectedness Closure Continuity Similarity Phi Phenom

xDepth Perception: The Visual Cliff

Binocular Cues: clues about distance using two eyes Retinal Disparity: the fact that the right and left eyes see

slightly different views of the object Convergence: the degree to which the two eyes must

converge to focus on the object

Monocular Cues: clues about distance based on the image in either eye Linear Perspective: parallel lines converge in the distance Relative Size: if two objects are the same, the larger one is

seen as closer Interposition: the nearer object overlaps the object farther in

the distance Texture Gradient: textures are coarser the closer they are Light and shadow Height in plane

Pictorial depth cues

Audition (Hearing) 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

The StimulusVibrations of sound waves Amplitude: loudness Wavelength: pitch Purity: timbre

Audition: The EarOuter Ear (pinna) Auditory Canal Eardrum

Middle Ear hammer anvil stirrup

Inner Ear oval window cochlea basilar membrane hair cells (cilia)

Audition: Pitch Perception

Place Theory (high pitch) the theory that links the

pitch we hear with the place where the cochlea’s membrane is stimulated

Frequency Theory (low pitch) the theory that the rate of

nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch

Touch

Numerous types of receptors lie in varying depths in the skin Four Basic Skin Senses Hot Cold Pressure Pain

Audition: Loss

Conduction Hearing Loss hearing loss caused by damage to the mechanical

system that conducts sound waves to the cochlea

Nerve Hearing Loss hearing loss caused by damage to the cochlea’s

receptor cells or to the auditory nerve

1time

10times

100times

1000times

32 64 128 256 512 1024 2048 4096 8192 16384

Frequency of tone in waves per second

Low Pitch High

Amplitude required forperception relative to 20-29 year-old group

Older peopletend to hearlow

frequencieswell but sufferhearing loss forhigh

frequencies

TasteTaste Sensations sweet sour salty bitter

Sensory Interaction the principle that

one sense may influence another

as when the smell of food influences its taste

The Stimuli: chemical substances that are solubleThe Anatomy: taste buds act as the receptors for taste (about every two weeks)Perception of taste & flavor Numerous factors can

impact the flavor of food (Ex: temperature of the food, texture, prior condition of the mouth, health state of the organism, smell)

The Tongu

e

Smell

Smell (Olfaction)

The Stimuli: chemical substances that are soluble The Anatomy: receptors are olfactory cilia which lie on the roof of the nasal passage and sinus Sense DOES NOT get filtered by thalamus Taste and smell interact to produce flavor

How We Locate Sounds

Localization of Sound Sound is heard in the

nearest ear first Sound is heard

loudest in the nearest ear

Perceptual Constancies: Size,Shape,Brightness, Color

Visual Perception: ConstanciesPerceptual Constancies: the ability to experience a constant perception even when what is reflected on the retina changes

Color: an object will be perceived as the same color even if the color reflected on the retina changes (ex: when an object is placed in the shade)

Size: an object will be perceived as the same size even if the size reflected on the retina changes (ex: dog running toward you is not seen as growing in size)

Shape: an object will be perceived as the same shape even if the shape reflected on the retina changes (ex: door opening toward you is still perceived as rectangular)

Visual Information Processing

Feature Detectors neurons in the visual

cortex respond to specific features

shape angle movement

Stimulus

Cell’s responses

Parallel Processing simultaneous processing of several dimensions

through multiple pathways color motion form depth

Touch

Skin Sensations pressure

only skin sensation with identifiable receptors

hot cold pain

Pain

Gate-Control Theory Theory that the spinal cord contains a

neurological “gate” that blocks pain signals or allows them to pass on to the brain

Body Position and Movement

Kinesthesis the system for sensing the position

and movement of individual body parts

Vestibular Sense the sense of body movement and

body’s position relative to gravity including the sense of balance Semicircular canals in ears

Parapsychology

Paranormal- beyond normal telepathy, ESP, out of body experience…