Sensation & Perception

Sensation is your window to the world!

Perception is interpreting what comes in your window!

SensationStimulation of

sensory receptors and the

transmission of sensory

information to the central nervous system (spinal cord & brain)

PerceptionPsychological

process through which we select,

organize and interpret our sensations

Bottom Up Processing

Information processing guided by higher level mental processes; as when we construct perceptions drawing on our experience and

expectations

Top Down Processing

Analysis that begins with the sense receptors and works up to the brain’s

integration of sensory information

Bottom-Up Processing• Also called feature

analysis.• We use the features

on the object itself to build a perception.

• Takes longer that top-down but is more accurate.

• Our brain instantly tries to put together a visual image using cues from our environment

You’ll know that the shape coming toward you is a human being before you’ll detect

the color of her hair or eyes or even her

gender.

Top-Down Processing• We perceive by filling

the gaps in what we sense.

• I _ant ch_co_ate ic_ cr_am.

• Based on our experiences and schemas.

• If you see many old men in glasses, you are more apt to process a picture of an old man (even when you may be in error).

PsychophysicsStudy of the relationship between

physical characteristics of stimuli and our psychological experience of them

Light brightnessSound volumePressure WeightTaste Sweetness

Weber’s Law

• Computes the Just Noticeable Difference.

• The change needed is proportional to the original intensity of the stimulus.

• The more intense the stimulus the more change is needed to notice the difference.

• 8% for vision.

Absolute Threshold

• The smallest amount of a stimuli we can detect about half of the time.

(Just Notable Difference) Difference Threshold

The smallest amount of change needed to detect in a stimulus before we detect a change.

Signal Detection theory

• Absolute thresholds are not really absolute.

• Things like motivation or physical state can effect what we sense.

• False Positives• False Negatives

My wife could sleep through a war, but if one of our sons even whimpers, she is up!!!

Sensory Adaptation

• Decreased responsiveness to stimuli due to constant stimulation.

Do you feel your underwear all day?

Subliminal StimulationHungry? Eat Popcorn and Drink Coca-Cola

Do movies have subliminal messages (“below threshold”) we can unconsciously

sense?

And without our awareness they have extraordinary suggestive powers?

Most likely is a hoax, but thinking it may be in the movie leads to a placebo effect,

which is what is actually making us hungry and thirsty.

Believing in the subliminal message makes us thirsty!

Vision• Our most

dominating sense.• Visual Capture

Transduction

• Transforming signals into neural impulses.

• Information goes from the senses to the thalamus , then to the various areas in the brain. Remember Ethan in Sky High. He

changes his body to slime. Solid form to liquid form. Change from one form of energy to another. Click the picture to watch power placement.

Phase One: Gathering Light

• The height of a wave gives us it’s intensity (brightness). • The length of the wave gives us it’s hue (color).• ROY G BIV• The longer the wave the more red.• The shorter the wavelength the more violet.

Getting the light in the eyeLight enters through the cornea!

Hearing

Our auditory sense

We hear sound WAVES

• The height of the wave gives us the amplitude of the sound.

• The frequency of the wave gives us the pitch if the sound.

The Ear

Transduction in the ear• Sound waves hit the eardrum

then anvil then hammer then stirrup then oval window.

• Everything is just vibrating.• Then the cochlea vibrates.• The cochlea is lined with

mucus called basilar membrane.

• In basilar membrane there are hair cells.

• When hair cells vibrate they turn vibrations into neural impulses which are called organ of Corti.

• Sent then to thalamus up auditory nerve.

It is all about the vibrations!!!

How do we locate sounds?

Sound waves strike one ear sooner and more intensely than the other from this

information, our brains compute the sounds location

Pitch Theories

Place Theory and Frequency Theory

Place Theory

• Different hairs vibrate in the cochlea when they different pitches.

• So some hairs vibrate when they hear high and other vibrate when they hear low pitches.

Frequency Theory

• All the hairs vibrate but at different speeds.

DeafnessConduction Deafness

• Something goes wrong with the sound and the vibration on the way to the cochlea.

• You can replace the bones or get a hearing aid to help.

Nerve (sensorineural) Deafness

• The hair cells in the cochlea get damaged.

• Loud noises can cause this type of deafness.

• NO WAY to replace the hairs.

• Cochlea implant is possible.

Touch

• Receptors located in our skin.

• Gate Control Theory of Pain

Taste

• We have bumps on our tongue called papillae.

• Taste buds are located on the papillae (they are actually all over the mouth).

• Sweet, salty, sour and bitter, and umami (meat).

Vestibular Sense

• Tells us where our body is oriented in space.

• Our sense of balance.

• Located in our semicircular canals in our ears.

Kinesthetic Sense

• Tells us where our body parts are.

• Receptors located in our muscles and joints.

Without the kinesthetic sense you could touch the button to make copies of your buttocks.

Perception

The process of organizing and interpreting information, enabling us to

recognize meaningful objects and events.

Illusions help us understand perception!

• Understanding illusions requires an understanding of how we transform sensations into meaningful perceptions– Size & distance– Principles of relative height– Grouping

Selective Attention

Selective Attention Focusing of conscious awareness on a

particular stimulus Cocktail Party Effect (listen to one voice,

among many)

Change Blindness

• An example of our lack of awareness of things going on around us… Change Blindness!

• Change Blindness: after a brief visual interruption, we fail to notice a change in the environment

• (Change Blindness Video)• Visual Capture: tendency of vision to

dominate the other senses

Absolute Threshold

• The smallest amount of a stimuli we can detect about half of the time.

(Just Notable Difference) Difference Threshold

The smallest amount of change needed to detect in a stimulus before we detect a change.

Weber’s Law

• Computes the Just Noticeable Difference.

• The change needed is proportional to the original intensity of the stimulus.

• The more intense the stimulus the more change is needed to notice the difference.

• 8% for vision.

Perceptual Ideas

Signal Detection theory

• Absolute thresholds are not really absolute.

• Things like motivation or physical state can effect what we sense.

• False Positives• False Negatives

My wife could sleep through a war, but if one of our sons even whimpers, she is up!!!

Top-Down Processing• We perceive by filling

the gaps in what we sense.

• I _ant ch_co_ate ic_ cr_am.

• Based on our experiences and schemas.

• If you see many old men in glasses, you are more apt to process a picture of an old man (even when you may be in error).

Bottom-Up Processing

• Also called feature analysis.

• We use the features on the object itself to build a perception.

• Takes longer that top-down but is more accurate.

Kids.exe

Click to see an example of bottom –up processing.

Gestalt Psychology

• We organize sensations into meaningful wholes (gestalts), that may exceed the sum of their parts and be regrouped into more than one perception

• Figure-Ground Relationships- to recognize an object, we must first perceive it as a figure against its surrounding stimuli (ground)– Reversible… a single stimuli can trigger more than one

perception!

Figure Ground Relationship

Our first perceptual decision is what is the image is the figure and what is the background.

Gestalt Psychology• Gestalt psychologists focused on

how we GROUP objects together.• We innately look at things in

groups and not as isolated elements.

• Proximity (group objects that are close together as being part of same group)

• Similarity (objects similar in appearance are perceived as being part of same group)

• Continuity (objects that form a continuous form are perceived as same group)

• Closure (like top-down processing…we fill gaps in if we can recognize it)

Constancy

• Tendency to see objects as unchanging while the stimuli from them change in size, shape, and lightness

• Shape Constancy• Size Constancy• Brightness Constancy

– Relative luminance: the amount of light an object reflects relative to its surroundings

Depth Perception

• Our ability to see objects in 3D despite their 2D representations on our retinas

Monocular Cues

• You really only need one eye to use these (used in art classes to show depth).

• Linear Perspective• Interposition• Relative size• Texture gradient• Shadowing

Perceived Motion

• Stroboscopic effect (flip book effect)

• Phi phenomenon • Autokinetic Effect

(if people stare at a white spotlight in a dark room, it appears to move.)

Binocular Cues

• We need both of our eyes to use these cues.

• Retinal Disparity (as an object comes closer to us, the differences in images between our eyes becomes greater.

• Convergence (as an object comes closer our eyes have to come together to keep focused on the object).

Depth Cues• Eleanor Gibson and her

Visual Cliff Experiment.• If you are old enough to

crawl, you are old enough to see depth perception.

• We see depth by using two cues that researchers have put in two categories:

• Monocular Cues• Binocular Cues

3-D Movies

• Simulate retinal disparity• Use 2 cameras to photograph each scene• Special glasses allow each eye to see only the image

from one camera• Each eye focuses = brain perceives one 3D image!• Perceptions are the constructs of our brains!

Moon Illusion

• Size and distance cues at the horizon make the moon seem further away when high in the night sky

• Moon closer to horizon will seem larger