Sensation&

PerceptionChapters 5&6

Sensation

Sensation a process by which our sensory

receptors and nervous system receive and represent stimulus energy

Perception a process of organizing and interpreting

sensory information, enabling us to recognize meaningful objects and events

SensationBottom-Up Processing

analysis that begins with the sense receptors and works up to the brain’s integration of sensory information

Top-Down Processing information processing guided by higher-

level mental processes as when we construct perceptions drawing

on our experience and expectations

Sensation- Basic Principles

Psychophysics study of the relationship between

physical characteristics of stimuli and our psychological experience of them

Light- brightness Sound- volume Pressure- weight Taste- sweetness

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

Sensation- ThresholdsSignal 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 detection depends partly on person’s

experienceexpectationsmotivationlevel of fatigue

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

Receptors

Environmental information (stimuli) exist in many forms:

•Air vibrations, gases, chemicals, tactile pressures

•The body receives these forms through specialized cells:

•Receptor cells

•E.g., taste buds

Receptors

Receptor sensitivity is subject to change

•Sensory adaptation

•Decline in receptor activity when stimuli are unchanging

•E.g., noticing a bad smell at first

Receptors

•Habituation

•Decline in sensory sensitivity at neural level due to repeated stimulation

•Different from adaptation since responsiveness can reappear if stimulation level increases or decreases

Vision- Stabilized Images on the Retina

Vision

Transduction- conversion of one form of energy to another

Wavelength- the distance from the peak of one wave to the peak of the next

Hue- dimension of color determined by wavelength of light

Intensity- amount of energy in a wave determined by amplitude brightness loudness

Vision- Spectrum of Electromagnetic Energy

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)

VisionPupil- adjustable opening in the

center of the eye

Iris- a ring of muscle that forms the colored portion of the eye around the pupil and controls the size of the pupil opening

Lens- transparent structure behind pupil that changes shape to focus images on the retina

Vision

VisionAccommodation

change in shape of lens focus near objects

Retina inner surface of eye light sensitive contains rods and cones layers of neurons beginning of visual information

processing

Vision

Acuity- the sharpness of visionNearsightedness

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

front of retinaFarsightedness

faraway objects seen more clearly lens focuses near objects behind retina

Vision

Farsighted Nearsighted Normal Vision Vision Vision

Retina’s Reaction to Light- Receptors

Cones near center of retina (fovea) fine detail and color vision daylight or well-lit conditions

Rods peripheral retina detect black, white and gray twilight or low light

Retina’s Reaction to Light

Optic nerve- nerve that carries neural impulses from the eye to the brain

Blind Spot- point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there

Fovea- central point in the retina, around which the eye’s cones cluster

Pathways from the Eyes to the Visual Cortex

Visual Information Processing

Feature Detectors neurons in the

visual cortex respond to specific features

shape angle movement

Stimulus

Cell’s responses

How the Brain Perceives

Illusory Contours

Visual Information Processing

Parallel Processing simultaneous processing of

several dimensions through multiple pathways

color motion form depth

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

Visual Information Processing

Trichromatic (three color) Theory Young and Helmholtz three different retinal color receptors

redgreenblue

Color-Deficient Vision

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

Visual Information Processing

Opponent-Process Theory- opposing retinal processes enable color vision

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

Opponent Process- Afterimage Effect

Audition

Auditionthe sense of hearing

Frequencythe number of complete wavelengths

that pass a point in a given time Pitch

a tone’s highness or lownessdepends on frequency

The Intensity of Some Common Sounds

Audition- The EarOuter Ear

Auditory Canal Eardrum

Middle Ear hammer anvil stirrup

Inner Ear oval window cochlea basilar membrane hair cells

Audition

Place Theory the theory that links the pitch we hear

with the place where the cochlea’s membrane is stimulated

Frequency Theory 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

Taste

4 basic sensations – sweet, sour, salty and bitter

All taste is a mixture of these

Taste is a chemical sense

Taste budsSensory interaction

Smell

Receptor cells inolfactory membrane

Nasal passage

Olfactorybulb

Olfactorynerve

Age, Sex and Sense of Smell

Women

Men

10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99Age Group

4

3

2

0

Numberof correct

answers

Women and young adults have best sense of smell

Touch

Skin Sensations pressure

only skin sensation with identifiable receptors

warmth cold pain

PainGate-Control Theory

theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain

“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

Drugs, surgery, acupuncture, electrical stimulation, massage, exercise, hypnosis, relaxation training, and thought distraction

LamazePsychological aspects of pain

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

position including the sense of balance

Vestibular sense - the sense of body movement and position, including the sense of balance•Semicircular canals – pretzel •Vestibular sacs – connect the canals to the cochlea•Move when we move our head•Hairlike receptors

Sensory Restriction Kissing Aphasia – ability to comprehend language Loss of a sense 1st experiments – Sensory Deprivation – disoriented,

hallucinations Sensory restriction does not disturb most people It reduces stress More open to positive influence Behavior modification REST – restricted environmental stimulation therapy Bottom-Up Chapter 6 Top-Down

If you had to lose one sense, which would it be?

If you could only have one, which would it be?

Perception

Selective Attention focus of conscious awareness on a particular stimulus

Perceptual Illusions

Perceptual Organization- Gestalt

Visual Capture tendency for vision to dominate

the other sensesGrouping

the perceptual tendency to organize stimuli into coherent groups

Perceptual Organization- Gestalt

Gestalt- an organized whole tendency to integrate pieces of information into

meaningful wholesGrouping Principles

proximity- group nearby figures together similarity- group figures that are similar continuity- perceive continuous patterns closure- fill in gaps connectedness- spots, lines and areas are seen

as unit when connected

Perceptual Organization

Figure and Ground organization of the visual field into objects (figures) that stand out from their surroundings (ground)

Perceptual Organization- Grouping Principles

Perceptual Organization- Grouping Principles

Gestalt grouping principles are at work here.

Perceptual Organization-Depth Perception

Depth Perception ability to see objects in three dimensions allows us to judge distance

Binocular cues retinal disparity

images from the two eyes differ closer the object, the larger the disparity

convergenceneuromuscular cuetwo eyes move inward for near objects

Perceptual Organization-Depth Perception

Visual Cliff

Perceptual Organization-Depth Perception

Monocular Cues relative size

smaller image is more distant interposition

closer object blocks distant object relative clarity

hazy object seen as more distant texture coarse --> close

fine --> distant

Perceptual Organization-Depth Perception

Relative Size

Perceptual Organization-Depth Perception

Perceptual Constancy

Perceptual Constancy perceiving objects as unchanging

despite changes in retinal imagecolorshape size

Perceptual Organization

Perceptual Organization-Muller-Lyer Illusion

Perceptual Organization- Size-Distance Relationship

Perceptual Organization-Brightness Contrast

Perceptual Interpretation

Perceptual Adaptation (vision) ability to adjust to an artificially displaced visual fieldprism glasses

Perceptual Set a mental predisposition to perceive one thing and not another

Perceptual Set-Schemas

What you see in the center is influenced

byperceptual set

Perceptual Set-Schemas

Flying Saucers or Clouds?

Perception without Sensation?

Extrasensory Perception controversial claim that perception can occur

apart from sensory inputtelepathyclairvoyanceprecognition

Parapsychology the study of paranormal phenomena

ESPpsychokinesis