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- 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

a constant for each sense: light intensity- 8%, weight- 2% tone frequency- 0.3% Just noticable difference has a proportion

to be met in order to sense difference

Weber’s Law

Classic and still identified today but it did not account for extreme values….175 watt and a 200 watt…

Ability to recognize difference diminishes….so in 1860s

Sensation- ThresholdsFechner’s Law- “upgrade” of

Weber’s law includes increase of jnd with extreme

measures/magnitude Adding the relationship of the perceived

magnitude to physical intensity of a stimuli

Same basic idea: ½ pound book in 2lb vs. 60lb backpack 1 voice in chorus of 10 versus 2 in 20

Sensation- Thresholds

Steven’s Power Law - upgrade to Fechner (Fechner’s law didn’t work for pain*, other stimuli)

Strength of a sensation related to the intensity of the stimuli raised to some power

So pain like electric shock you will sense a a small change at higher intensities than at the lower intensities when more may be needed to recognize difference

Fechner

Stevens

Sensation - Thresholds

Note that one of the implications of Steven’s law is that with higher levels of pain you get MORE sensitive!

Sensory adaptation- diminished sensitivity with constant stimulation

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- ThresholdsSignal Detection Theory

Assumes TWO things going on: 1. sensitivity to stimulus (physical) 2. response bias – also called decision

criterion (psychological)

Can measure & plot these in a Receiver Operating Characteristic curve (ROC curve)

Vision

Transduction- conversion of one form of energy to another (for us, it’s specifically: converting physical energy to neural impulses)

Properties of light and vision Physical Psychologicalintensity brightnesswavelength hue (color)wave purity saturation

Vision

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

Amplitude - the height (strength) of a wave

Hue- perceived “color” of the lightIntensity- amount of energy in a wave

determined by amplitudeSaturation - perceived “purity” of a color

(e.g. pastels have low saturation)

Vision- Spectrum of Electromagnetic Energy (quantum particle/waves)

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 the 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

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

Saccades - quick eye movements

Retina’s Reaction to Light

Bipolar cells- neurons that combine info from multiple receptors

Ganglion cells – neurons that combine info from multiple bipolar cells.

Optic nerve – bundle of axons of the ganglion cells that carry info from retina to brain.

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

*Why pirates wore eyepatches? Arrrr…

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

Vision- Stabilized Images on the Retina

Retina’s Reaction to Light

Receptive fields – regions in which receptors respond to light

Lateral inhibition – receptor (or neuron) making it’s neighbors less sensitive Helps in things like edge detection

Visual Information Processing

Feature Detectors neurons in the

visual cortex respond to specific features

shape angle movement

Stimulus

Cell’s responses

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

Neural pathways (multiple!) Optic nerve through optic chiasm

(crossover), becomes the optic “tract” then…

Primary visual cortex (striate cortex) then splits into…

The “what” path (thru temporal lobes) The “where” path (up into parietal lobes)

Visual Information Processing – Color vision

Trichromatic (three color) Theory The Young–Helmholtz theory three different retinal color receptors

sensitive toredgreenBlue

Visual Information Processing – Color vision

But Tri-chromatic didn’t explain afterimages or color-blindness! So…

Opponent Process Theory Black-white receptors (for brightness &

saturation) Red-green receptors (for hue) Blue-yellow receptors (for hue)

Opponent Process- Afterimage Effect

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

Visual Information Processing – Color vision

So who’s right??? Turns out they’re both right:

Tri-chromatic theory works in the retina Opponent process works in the higher visual

processing parts of the brain Together they explain what we know about

color vision quite well.

Audition

Auditionthe sense of hearing

Properties of sound and hearing Physical Psychologicalintensity loudnesswavelength pitchwave purity timbre (tone)

Audition

Frequencythe number of complete wavelengths

that pass a point in a given time Pitch

a tone’s highness or lownessdepends on frequency

Timbre - tonal quality; “richness”

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

Audition

So who’s right? They’re both probably right: At low frequencies: frequency

theory At high frequencies: place theory At middle frequencies: both

How We Locate Sounds

How we locate sounds

Two cues: Differences between the two ears

in loudness Differences in the arrival time at

the ears

Audition

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

Audition Older people tend to hear low frequencies well

but suffer hearing loss for high frequencies

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

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

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

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

SmellLess important in humans than

animals but we still can detect:Pheromones

Smell-communicated chemicals secreted by organisms

People can often identify gender by smell of sweaty hands or articles of clothing!

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