Chapter 4 Powerpoint: Intro and Vision

Sensation and Perception

Detect

Environment

Organizing

Interpreting

Sensory InformationSenses

Kinesthesis

Vestibular Sense

processing

attention

tastesmell

hearingbrain

touchsight

Warm up

What is sensation? What is perception?

DefinitionsSensation-- the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.

Perception--the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.

Do we process everything our senses take in?

Top-down processingInformation processing guided by higher-level

mental processes, as when we construct perceptions drawing on our experience and expectations.

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

Bottom- up processing

Top Down vs. Bottom Up Processing

THEORIES OF SELECTIVE ATTENTION

Bottom up Theories

Top Down Theories

Top Down Theories of Attention• These theories say that perception starts from the more complex• Selective Attention/ Attenuation Theory:

• We process everything but everything doesn’t reach the highest centers of processing

• You “pick and choose” what to process the most

• Ex. Cocktail Party Phenomenon

Bottom Up Theories of Attention• This theory says that perception starts with sensation• Because so much information is coming in, some sensory

information is never processed• Filter Theory– We can’t process everything

Example

Selective Attention• the focusing of conscious awareness on a particular

stimulus.• You cannot pay attention to everything, only some things

Psychophysics

The study of the relationship between physical characteristics of stimuli and our psychological experience of them

Light- brightnessSound- volumePressure- weightTaste- sweetness

Sensation- Thresholds

Absolute Threshold minimum stimulation needed to detect a particular stimulus 50% of

the time

Difference Threshold minimum difference between two stimuli required for detection 50%

of the time just noticeable difference (JND)

Selective Attention• List 10 things you saw in the picture…..

Inattentional Blindness

• Change Blindness (failing to notice changes in the environment)

• Choice Blindness• Choice Blindness Blindness

failing to see visible objects when our attention is directed elsewhere.

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 detection depends partly on person’s

experience expectations motivation level of fatigue

Primingthe activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response.

ThresholdsSignal Detection•Signal-detection theory

• Ratio of “hits” to “false alarms”

Signal Detection is not necessarily true…

Subliminal When stimuli are

below one’s absolute threshold for conscious awareness

0

25

50

75

100

Low Absolutethreshold

Medium

Intensity of stimulus

Percentageof correctdetections

Subliminal stimuli

Sensation- Thresholds

Weber’s Law- to perceive as different, two stimuli must differ by a constant minimum percentage light intensity- 8% weight- 2% tone frequency- 0.3%

Sensory adaptation- diminished sensitivity as a consequence of constant stimulation

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Wrap-up

TICKET OUT: What are sensation and perception? How does our perceptual system help us to interpret the world around us? Explain.

Short Video About Sensation and Perception

Warm upHow does the visual system work?

Vision

EYE

Vision Pupil- 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 (dilates in response to changing light intensity)

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

Cornea - outer covering of the eye Retina - the light-sensitive inner surface of the eye, containing

the receptor rods and cones plus layers of neurons that begin the processing of visual information.

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

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

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

How does the eye work?

?

Distal Stimulus– the object in the outside world

Proximal Stimulus– the object as it is projected on the retina (upside down)

This is how we see

Animation of how this works...

TERMS: Distal stimulus, proximal stimulus, fronto-parallel plane, Distal Object, Percept

Pathways from the eyes to the visual cortex

Visual Information ProcessingFeature Detection

•Feature detectors

Visual Information ProcessingParallel Processing

•Parallel processingsimultaneous processing of several aspects of a problem simultaneously

• Blind sight

What is color?

What is color?• Color is the psychological attribute given to our response to

different wavelengths of visual light• It is psychological because it is perceived • Humans can only perceive colors on the visual spectrum.

Perception has to do with light getting reflected off an object and onto the different types of cones in the eye

Electromagnetic Energy Spectrum

Electromagnetic Energy Spectrum

The Stimulus Input: Light EnergyTransduction conversion of one form of energy to anotherIn sensation, transforming of stimulus energies into neural impulses

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

Hue (color)

Dimension of color determined by wavelength of light

IntensityAmount of energy in a wave determined by amplitude

The Physical Property of Waves

The Physical Property of Waves

Retina’s Reaction to Light- Receptors

Rodsperipheral retina detect black, white and gray twilight or low light

Conesnear center of retina fine detail and color visiondaylight or well-lit conditions

Rods and Cones

Rods are sensitive only to black and white and are sensitive to light and dark.

Cones come in three types, each sensitive to a different color: red, green, and blue. Cones are concentrated in the center of the retina, while rods form the periphery of the retina.

The EyeThe Retina

•Rods and Cones

RodsCones

Rods versus Cones

How Cones Perceive colors

Different “colors” of light stimulate the different cone cells in different combinations, thus accounting for the different colors we see.

There are 3 different types of cones that respond to different types of wavelengths.

•Short-wavelength cone receptors β•Middle-wavelength cone receptors γ•Long-wavelength cone receptors. ρ

This is called the Trichromatic Theory of Color Vision

The Retina’s Reaction to Light

Color Vision

•Young-Helmholtz trichromatic (three color) theory• Red – Green - Blue• Monochromatic vision • (only can perceive 1 of 3)

vision• Dichromatic vision (2 of 3)• People who can’t read the

number in the box couldbe color blind

Color Vision

•Opponent-process theory• Three sets of colors

• Red-green• Blue-yellow• Black-white

• Afterimage

Color Blindness• The inability to differentiate certain colors• More common in men because on x chromosome (women need 2

genes to inherit but men only have 1 x chromosome)• There are three types:

• Red/ green (95%)• Blue/ yellow• All colors

Color Blindness Simulator

WARM UP:

1.On worksheet fill in definition and one example.

2.How does the eye work like a camera?

Visual Information Processing• There are 4 different “cues” to perception.

They are:- Shape Constancy- Size Constancy- Color Constancy- Monocular and Binocular Depth Cues

How do they work???

Vision

Accommodation- the process by which the eye’s lens changes shape to help focus near or far objects on the retina

Acuity- the sharpness of vision

Nearsightedness- condition in which nearby objects are seen more clearly than distant objects because distant objects in front of retina

Farsightedness- condition in which faraway objects are seen more clearly than near objects because the image of near objects is focused behind retina

Vision

Normal Nearsighted Farsighted Vision (myopic) Vision (hyperopic)

ILLUSIONS

What is an illusion?

What is an illusion?• Also known as Visual Illusions• involves visual deception.• When looking at an illusion our visual system

can perceive misleading visual effects • There is no one good reason• Because Perceptual Constancies (size, shape,

color, etc.) are just merely cues we can misinterpret what we look at

• Also our visual system groups items (gestalts) and this can cause misperception

DEMOS….

• Spinning wheel illusion (after image)

• Magic coins illusion (after image)

• Wundt-Jastrow illusion (effect of context/contrast on perception)

Ponzo Illusion

Ambiguous Figures• In some illusions there is not enough information in the image

to make a decision as to the “best” interpretation• Shows us the importance of “interpretation”• How we see it depends on how we perceptually organize.• Also depends on the context in which we just saw it and

individual bias, etc.

Vase or Face?

“Yes or No” Sculpture by Markus Raetez

Reversible figures

• Follow the same principle

Is the dark side in the front or the back?

How the Brain Perceives

Impossible Figures

• Follow the same principle of not enough information so we interpret it

• Usually a 2-D figure which interpreted by the visual system as representing a projection of a three-dimensional object that is not geometrically possible

Devil’s Tuning Fork

M.C. Escher

“Relativity”

How many legs does this elephant have?

Penrose Triangle (Ernst, 1987)

Hermann Grid Illusion Hermann (1870)

Explanation

Researchers have traditionally used what is known as lateral inhibition to explain why people see these gray areas. This phenomena demonstrates a very important principle of perception: we don't always see what's really there. Our perceptions depend upon how our visual system responds to environmental stimuli and how our brain then interprets this information. New theories suggest there might be a better explanation.

Muller-Lyer Illusion

Zollner Illusion

Illusory Contours

Ponzo Illusion

Ames Room

How it actually looks

• The Ames room forms an identical image of a normal cubic room on your retina even though it is not cubic.

How does it work?

STROOP EFFECT