Sensation and Perceptionchapter 6

Sensation: your window to the world Perception: interpreting what comes

in your window.

Sensation

• The process by which our sensory receptors and nervous system receive stimulus from the environment. (stuff inputed from our 5 senses)

Bottom-Up processing

• a progression from individual elements to the whole (start small then work your way up). Visually, that would mean noticing lines, angles, colors etc.

• Basically……..Sensory detection

Top-Down processing

• Start with the forest and work your attention down to the individual tree.

• Basically…..the brain’s perception of what the info brought in by the 5 senses!!! The meaning!

Absolute Threshold

• The minimum stimulation needed to detect a stimulus 50% of the time.

• EX: the flame of a candleon a clear night 30 milesaway

Signal detection• Detecting the presence of a faint stimulus

amid background stimulus. • • It depends on our psychological state

(alertness, expectations, experiences, motivations)

• EX: hearing a crying infant is lower when you become a parent!

Subliminal stimuli

• Can we sense stimuli below our absolute thresholds? YES

• Can advertisers influence us with “subliminal messages”? Not really

• How does it affect us? It can prime us.• In one experiment, subliminally emotionally positive scenes (kittens…) or

negative scenes (dead body) were flashed before viewing a pic of a face. Those faces that had a flash of a postive image (which to them looked like a flash of light) rated the faces as nicer.

Difference threshold

• The least amount of stimulation needed to notice that a change has taken place

• Important for certain tasks like piano tuning

• EX: knowing your child’s voice among all the other’s

Weber’s Law• The idea that, to perceive a

difference between two stimuli, they must differ by a constant percentage; not a constant amount

• Ex: Which would you notice on a purchase of a $20,000 car?

Car mats- $100Backseat DVD player $500Alloy wheels $2000Window tinting- $200

Sensory Adaptation

• Our sensitivity to unchanging stimuli gradually diminishes

• Why do the senses seem toattend only to novel stimuli?

Do you feel your underwear all day?

Question:

• If sensory adaptation occurs, why then, if we stare at an object, does it not vanish from sight?

• Answer: The eye constantly quivers to counteract this possibility…we just don’t realize it!!!

Selective Attention• The focusing of conscious awareness on a particular

stimulus.• The brain really only focuses on ONE main thing at a

time!!!!!

Selective Attention

• The brain makes what you focus on the foreground and everything else the background.

• Can you switch these??

An example of selective attention is:

Cocktail Part Effect: ability to listen to one voice among many.

Vision• Vision-Our most

dominating sense.

• Visual Capture-this is why we fall for ventriloquists

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.

Transduction

• Transforming signals into neural impulses.

Information goes from the senses to the thalamus , then to the various areas in the brain.

Phase Two: Getting the light in the eye

Phase Three: Transduction

Order of cells in the retina

• rods, cones bipolar cells ganglion cells

• Can you create a way to recall their order?

R C B G

Phase Four: In the Brain

• Goes to the Visual Cortex located in the Occipital Lobe of the Cerebral Cortex.

• Feature Detectors.• Parallel ProcessingWe have specific cells that

see the lines, motion, curves and other features of this turkey. These cells are called feature detectors.

What are feature detectors?

We have specific cells in the brain that see the lines, motion, curves and other features of this turkey. These cells are called feature detectors.

Motion detectors

• For example, there are motion detector cells that fire for a variety of motions. Here’s one for movement.

• Let’s see what happens when we over use them: stare at the center of this for 30 sec.

• http://www.michaelbach.de/ot/mot_adaptSpiral/index.html

What is parallel processing?

• Brain’s ability to perceive several features simultaneously

Example:

• movement• Color• Size• direction

Color Vision

Two Major Theories

Trichromatic Theory

Three types of cones:• Red• Blue• Green

• These three types of cones can make millions of combinations of colors.

Opponent-Process Theory• We cannot see certain colors together in

combination (red-green, blue-yellow, and white-black). These are antagonist/ opponent colors. It explains afterimages!

Tube and marble example.

Amplitude is how loud the sound is. The higher the crest of the wave is the louder the sound is. It is

measured in decibels.

Cilia- receptors cells in 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 called cilia.

• When the cilia vibrate, they turn vibrations into neural impulses.

It is all about the vibrations!!!

How do we perceive differences in pitch?

There are two theories……..

1. Helmholtz’s Place Theory

• We hear different pitches because different sound waves trigger activity at different places along the cochlea’s basilar membrane.

The Place Theory

• Only explains HIGH pitches!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

2. Frequency Theory

• We sense pitch by the basilar membrane vibrating at the same rate as the sound.

• Only explains LOW pitches!!!!!!!!

So….what about all the pitches in between?????

• This problem can be explained using the volley principle.

• Between the two (placeand frequency) they thinkthe brain figures out the ones in between…..

Why do we have two ears?

• To determine the direction of a sound!!!!

Two types of hearing loss:

1. Conduction Hearing Loss: caused by damage to mechanical system of ear (little bones).

2. Sensorinueral hearing loss: caused by damage to cochlea’s receptor cells or to auditory nerves.

Which type of hearing loss would be due to age?

• Why?

Which type would be due to the accumulated exposure to

loud sounds?

Smell and Taste

Why do we study smell and taste together?

SENSORY INTERACTION: smell and taste

• the principle that one sense may influence another.• Taste and smell are chemical senses.

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.

Does “Sweet N. Low Taste Bitter?Are You a Picky Eater?

Maybe you’re a “supertaster”!!!

• http://courses.bfwpub.com/myers9e

PTC Strips

Sensitivity to taste

• Decreases due to:

SmokingDrinkingage

But what about smell?

It is a chemical sense

What are the receptor cells for smell?

Cilia in your nose.

Kinesthetic Sense

• Tells us where our body parts are.• Receptors located in our muscles and

joints.

• Do they know they are si sitting Indian style?

Vestibular Sense

• Tells us where our head (and thus body) is oriented in space.

• Gives us our sense of balance.

• Located in our semicircular canals in our ears.

Touch

• How is it different from the other senses??

1. It has NO specific receptors.2. Only pressure has identifiable receptors3. SKIN sensations are variations of pressure, warmth,

cold and pain4. It’s important for infant growth (premature infants

gain weight faster when touched)

Gate-control theory

Have you ever hurt yourself and felt the pain later?

•his theory says that pain is sent through small fibers while other sensory info goes through large fibers. When injured, the large fibers can “close the gate” of the small fibers, thus blocking some of the pain

Perception

The process of organizing and interpreting information, enabling us to

recognize meaningful objects and events.

Muller-Lyer illusion

Why do we fall for this illusion?

Ponzo illusion

Figure-ground principle:

states that we organize our perceptions into figure and background

Figure Ground Relationship

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

Gestalt Psychology• Gestalt means “an organized whole”• These psychologists emphasize our tendency

to integrate pieces of information into meaningful wholes

Gestalt Philosophy

The whole is greater than the sum of its parts

Gestalt and attention… Aoccdrnig to a rscheearch at

Cmabrigde Uinervtisy, it deosn’t mttaer in what oredr the ltteers in a word are, the olny iprmoetnt tihng is that the frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can still raed it wouthit porbelm. This is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the word as a wlohe.

Gestalt Psychology (grouping principles)

• 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)

Gestalt demonstration:

• Divide into groups.

• Each group is given a gestalt principle of grouping. That group must demonstrate the grouping principle.

Depth Perception

• The ability to see objects in three dimensions although the images that strike the retina are two dimensional.

• Allows us to judge distance.

Visual Cliff

Depth:How do we transform two-dimensional

objects to three-dimensional perception?

• Binocular Cues: depth cues that depend on two eyes

•Monocular Cues: depth cues that depend on one eye

Binocular Cues:

1. Retinal Disparity

2. Convergence

1. Retinal Disparity

. a binocular cue for seeing depth.

• The closer an object comes to you the greater the disparity, or difference in the angle is between the two images.

2. Convergence

• when objects are closer to you, there is more tension in the muscle of your eyes

Monocular Cues:• Brain only needs ONE eye to perceive depth• Artists use these to create depth• They are 7:

• Relative height• Relative size• Linear perspective• Motion parallax (relative motion)• Interposition• Light and shadow• Texture gradient

Linear perspective: objects farther away tend to become

smaller and come to a point

Texture Gradient: objects farther away appear less

clear, hazy

Light and shadow: shadow means depth

Relative size: when objects are the same size,

the one that is closer looks larger

Motion parallax: objects farther away move more

slowly

Interposition (overlay): one object in front of another

appears closer

Relative height: objects higher in our field of vision

are farther away

Which monocular cue?

Stroboscopic motion

Perceptual Constancy

• Color Constancy• Size Constancy• Lightness Constancy• Shape Constancy

• Thanks to perceptual constancy, we still recognize an object even if the object’s size, color, lightness or shape varies

Perceptual Set

How our

•-expectations•-contexts•-emotions

influence our perception

Your “lens” for viewing the world

If you grew up in an abusive home, give examples of what your “lens” about life might be different?

ESP Terms: Parapsychology

• Telepathy-mind-to-mind communication• Precognition- perceiving future events • Clairvoyance-perceiving remote events (like

know that someone has just died)• Telekinesis- moving objects using your mind