AP Psych Prep 4 - Sensation and Perception

8/13/2019 AP Psych Prep 4 - Sensation and Perception

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SENSATIONAND

PERCEPTION

AP Psych Prep. 4


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Overview:

Our senses gather information and tell us aboutour world and body.

Sensoryorgansreceive

stimuli

Stimulitransformedinto neural

impulses

To Thalamusin the Brain

To specificsensory brain

areas


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General Sense and Perception Concepts:

Sensory Adaptation senses respond less stronglybecause of constant stimulation (e.g. Smell)

Sensory Habituation reduced perception ofsensory signals because of changed attention tothem. (e.g. touch clothing, socks)


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General Sense and Perception Concepts:

Our attention is closely connected to ourperception of sensory information. We get muchmore sensory information coming into our brains

than we can pay attention to at one time.

Cocktail party phenomenon the phenomenonwhere our brains monitor sensory informationoutside our conscious awareness and brings thingsto our attention if they are important. (e.g. yourname in loud classroom)


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General Sense and Perception Concepts:Sensation Vs. Perception

Differences debated, but we can go by:

Sensation activation of our sensory organs,conversion into neural signals, transmission ofsignals to the brain

Perception process of decoding andunderstanding those signals in our brains


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Sensation - Types of Senses:

Energy Senses vision, hearing, touch (detectinglight, sound waves, pressure energy)

Chemical Senses taste, smell (chemical detection)

Vestibular and Kinesthetic Senses body senses

(body placement, orientation)


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Vision:

Light from some source enters our eyes, or bouncesoff objects in our world and then into our eyes.

If there is nolight, there can

be no vision.


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Process of Vision:

Light passes through cornea, a protective cover thatalso helps to focus light (lasik/lasek surgery)

Then through pupil, the hole surrounded by the

colour of your eye (iris) . This hole can dilate (getbigger) to let more light in, or smaller to let less lightin.

Finally, it passes through the lens which is the mainfocusing piece. Muscles can change the shape of lensto focus the image clearly on the back of the eye.(switch distance focus)


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Process of Vision:


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Process of Vision:

Light is focused on the back of the eye on the retina.Retina is made of important light-detecting cells.

These cells are activated when they are hit by light,and this causes them to send neural signals.

Different kinds of cells:

Cones detect colour (5-6% of retina)

Rods simply react to light; detecting shape, etc.


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Process of Vision:

More cones in the back center of eye.

Especially in fovea, the central focus point that is

slightly indented, and has high concentration of conecells. We see colour best here (coloured pencil test).

Peripheral (edge) vision is mostly rods, so mostly

black and white vision (and higher ability to detectlight)


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Process of Vision:

Ganglion cells axons = optic nerve bundle of wires(axons) that takes sight information to the brain.

Blind Spot where the optic nerve leaves the eye.Because of cord, no cones or rods in this spot, so no

vision here. (But we have two eyes...) Blind SpotTest

LightSensitiveCells

Bipolar Cells GanglionCells

Brain(Thalamus)

OccipitalLobe (VisualCortex)


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Blind Spot: Human vs. Octopus


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Process of Vision:Source of Light


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Process of Vision:

The image that is projected onto the retina of our eyes

is flipped and upside-down. Ourbrainsflip theimage back after they get the signals.


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Process of Vision:

Our retina is divided into two. Left side of eachretina

goes to the right side of the brain, and viceversa. (Remembersplit brain patients)

Optic Chiasm where the two opticnerves cross

FocusPoint


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Influences on Vision:

Amount of light = how bright things seem Wavelength of light = the colour we see

We can only see part of the electromagnetic spectrum -

visible light

Objects appearto be the colour

of the wavelengthof light they

reflect, becausethats the light

that hits our eye


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Influences on Vision:

Long Wavelength lightShort Wavelengthlight

red, orange, yellow, green, blue, indigo, violet


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Theories of Colour Vision:

Trichromatic theory older theory three types ofcones that detect blue, red and green light.

These three in different amounts give us all thecolours we can see.

However this doesnt explain afterimages or colorblindness (red-green

or blue-yellow colorblindness).


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After Image Trial:

Stare at the dot without blinking for about 30 seconds,then look at a blank white space (paper)


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Opponent Process Theory cells for red / green andblue / yellow are tied together in pairs.

Chemical process going one way = red, the other way= green.

When you stare at the red picture, the red process isoverused. So after that, the process reverses, showingthe green colour.

When signaling red, cant signal green.


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Opponent-Process Theory

Also helps explain red-green or blue-yellow

colorblindness.

Many researchers think both explanations can beuseful to explain colour sight. Exact truth is not

completely clear yet.


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Process of Vision:

The signals travel from our eyes, along the opticnerve, through the thalamus (lateral geniculatenucleus (LGN)), and to the occipital lobe at the backof the brain.

There, we have specialized cells that react to certainstimuli. E.g. movement, horizontal or vertical lines,

etc.


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Process of Vision:

These are called feature detectors. They detect certainfeatures of our environment from the visual infoprovided by our eyes.

Feature detectors explored by David Hubel andTorsten Wiesel.

All the detected features are combined in higher levelprocessing areas, and thats where our perception of

vision comes from.


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Auditory Sense / Hearing:

Also detects waves, but sound waves, instead of lightwaves.

Sound waves come from vibration, travel through theair to our ears.


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Auditory:

Sound waves have amplitude and frequency

Amplitude height of

waves;loudness

Frequency length of waves

(Megahertz);pitch of sound


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Auditory Sense:

Sound waves collected by pinna (outer ear), and thenthey travel down ear canal / auditory canal.

They then hit the ear drum (tympanic membrane) andvibrate it. This vibration passes to ossicles (inner earbones).

Hammer(malleus)

Anvil(incus)

Stirrup(stapes)

OvalWindow

Cochlea


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Auditory Sense:

Cochlea coiled shell-shaped organ, filled with fluid.

Inside are hair cells that are moved by the fluid whenvibrations pass through. Neurons connected to thehair cells fire when they move, sending signals to theauditory cortex of the brain.

Hair cells and neurons = organ of Corti


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Two Theories of Sound Detection:

How do we detect different types of sound?

Place Theory idea that diff. parts of the cochlearespond to different frequencies of sound. This seemsto be true for high tones.

Frequency Theory idea that cells fire signals at

different speeds in response to diff. frequencies ofsound. Seems to be true for low tones.


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Auditory Sense - Deafness:

Understanding how hearing works helps us see howhearing problems can occur.

Problems conducting vibrations to the cochlea =conduction deafness; relatively easy to treat.

Problems in cochlea or sound detection cells = nerve

or sensorinerual deafness; we dont know how to gethair cells to re-grow.

Hair cells can be damaged permanentlyby loudnoises. Permanent hearing loss is possible.


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Touch:

We have different types of nerve ending sensors in ourskin that detect heat, cold, pressure, and pain. Thesefeed information to our brains.

Different areas of our bodyhave different amount ofreceptors.

Hands, fingertips, feet,face, lips high number

Back, elbow, etc. - low


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Sensory Input

Many moresensors in someareas of our

body


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Touch:

Gate Control Theory of Pain- some pain messageshave a higher priority than others.

If no high priority message, low gate is open and thatpain gets through.

But if high priority message comes, the low gatecloses, stopping the low priority message, and thehigh priority message gate opens to let it through.

(Gates are just a metaphor, not real structures) E.g. sore leg from exercise yesterday vs. cut hand.


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Touch:

Pain is a very useful sense. It acts as a warning to helpus avoid damaging our bodies.

Our brains can alsoinfluence ourexperience of pain,including through

natural pain-killingchemicals.(endorphins)


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Taste / Gustation:

A Chemical Sense. Taste involves detecting chemicalsfrom food we eat.

Papillae are bumps in our mouths (mainly on ourtongues) that include taste buds that detect chemicals.

We detect 5 types of tastes: sweet, sour, bitter, salty,and savory (meaty; also called umami).

Different taste buds will be more specialized to detectcertain tastes.


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Taste / Gustation:


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Taste / Gustation:

Our sense of taste actually combines taste and smell.

If youre sick and cant detect smell well, your sense oftaste for food will be very dull.


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Smell (Olfaction):

Another Chemical Sense. Involves detecting chemicalsfrom the air.

We have many types of olfactory receptor cells(probably around 100) in mucous membrane deep

inside our noses.

These detect chemicals, and send it to the olfactorybulb, and then to the amygdala and hippocampus.

(not to the thalamus like other senses) This may be why smell can be so strongly connected to

memory.


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Smell (Olfaction):


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Body Position Senses:

Vestibular Sense tells us about our bodysorientation. Three canals in the inner ear with fluidtell us how our head is oriented in terms of gravity.

Fluid in these semi-circular canals moves when our

heads move, giving usorientation info.

Dizziness and nausea canbe caused by too muchmovement.


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Body Position Senses:

Kinesthetic Sense - gives us specific informationabout where parts of our bodies are. Sensors in our

joints and muscles give information about how ourarms, legs, etc. are positioned.


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Perception:

How we interpret and understand sensations.

Psychophysics study of the interaction of sensationsand our perceptions of them.


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Thresholds:

Absolute Threshold the smallest amount of stimuluswe can detect 50% of the time.

Stimuli below this level are called subliminal. Somesmall subliminal messages can influence our

behaviour (e.g. picking a word from a list), but theresnoevidence that complicated messages can alter

peoplesbehaviour in major ways (e.g. advertising)


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Thresholds:

Absolute thresholdfor light is a singlecandle 48 kilometers

away on a perfectlydark night.


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Thresholds:

So a very strong stimulus will need to change morebefore you notice the change.

A weak stimulus can change just a bit before younotice.

*In both cases, the same proportion.

Consider a drink with sugar in it.

Just-Noticeable Difference for Vision 8% For Hearing is 5%


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Perception

Perception in the real world is influenced by thingslike attention, competing stimuli, etc. (responsecriteria)

Signal Detection Theory explores these influencesand how they might influence our rates of correct orfalse detection of stimuli.


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Perception

Signal Detection Theory:

False Positive, False Negative, Hit, Correct Rej.


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What Do You See Here?


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Top-Down Processing


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What Do You See Here:


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Principles of Visual Perception:

How we perceive visual stimuli is pretty well

understood. Has been studied a lot. Here are someprinciples of visual perception.

Figure-ground

relationship same stimuli,our minds canswitch our

perception of it.


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Gestalt Rules:

C


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Constancy:

Even though we receive slightly different signalsbased on how close the object is to us, the angle fromwhich we view it, and the light that bounces off theobject (outside in bright sunlight vs. inside in a dim

place).

Based off our background knowledge of the object.Objects we know well.

Size Constancy, Shape Constancy, Brightness Con.

P i d M i


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Perceived Motion:

Our brains do math to detect the motion of objects.Often very accurate.

Occasionally, our brain can be tricked to perceivemotion when in fact there is no real motion.

Stroboscopic effect still images with differences

presented fast enough will seem to be moving. E.g.Movies.

P i d M i


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Perceived Motion:

Phi Phenomenon when a series of light bulbs turnedon and off at a fast rate will look like one moving light

bulb.

Autokinetic Effect in a dark place, with onepoint of light, if you stareat it, the light will seemto move

D h C


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Depth Cues:

Very important part of our visual perception. Tell us 3D information about our world, which things

are farther and closer to us, relative position, etc.

Depth perception develops early, near the time we cancrawl as infants.

Animals commonly get this earlier than humans.

D th C


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Depth Cues:

Eleanor Gibson Visual Cliff Experiments

D th C M l V Bi l


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Depth Cues: Monocular Vs. Binocular

Monocular Cues require only one eye. Often used inart to show depth.

1. Linear perspective parallel lines come together inthe distance.

2. Texture Gradient Cue

textures closer to us aremore detailed


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D th C M l V Bi l


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Monocular Cues

5. Shadow canshow us depth,

and also relativeposition of

objects

D th C M l V Bi l


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Binocular Cues comefrom the fact that wehave two eyes

Binocular Disparity /Retinal Disparity theimage of objects in eacheye will get more andmore different as theobject gets closer toour eyes.

D th C M l V Bi l


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Binocular Cues

Convergence closer objectsrequire us to moveour eyes inwardmore, so our brainuses eye position todetermine how closesomething is to us.

(IPD = InterPupillary Distance)

C lt al Diffe ence in Pe ception


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Cultural Difference in Perception

Which of these lines is longer?

Cultural Differences


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Cultural Differences

Cultures with a lot of right angles in architecture tendto be perceptually fooled by this Muller-Lyer illusion

While cultures that dont have a lot of right angles in

architecture dont have this trouble.

P t l Ill i


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Perceptual Illusions

There are also other timeswhen our perception is

mislead by perceptual cues.

But in normal situationsour brain is well designed to

perceive the world in ways

that are accurate.

Documents

AP Psych Prep 4 - Sensation and Perception