Sensation and Perception Chapter 3


Sensation and



The process by which our sensory and nervous systems receive stimuli/info from the environment

A person’s awareness of the world through their senses.


The process of selecting, organizing and interpreting sensory information

How you make sense of your sensory information.

Perception uses

Top-Down Processing

Information processing that focuses on expectations and experiences in interpreting incoming sensory information

Terms to Remember


Transforming signals into neural impulses.

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

Sensory Adaption:

Decreased responsiveness to stimuli due to constant stimulation.

Coctail-Party Effect (phenomenon)

Ability to focus one's listening attention on a single talker among a mixture of conversations and background noises, ignoring other conversations.

Form of selective attention .

Vision Basics

Stimulus (input) is light energy

Is the dominant sense in human beings.

The process involves several steps:

Step 1:

Gathering Lightlight is reflected off of objects and gathered by the eye

Step 2: Within the eye:

Cornea- transparent protective coating over the front part of the eye

Pupil small opening in the iris through which light enters

Iris-colored part of the eye

Lens- transparent part inside the pupil- focuses light onto the retina

Retina lining of the eye containing receptor cells sensitive to light.

Step 3: Transduction

Receptor cells- respond to a specific energy

Rods- receptor cells in the retina- night vision, brightness

(black/white) PERIPHERAL vision

Cones- receptor cells in retina- color vision

Fovea- area of the retina that is the center of the visual field- Also the most clear vision.

Optic nerve- bundle of axons and ganglion cells- carry neural messages from the eye to the brain

Blind spot- no receptors- where the optic nerve leaves the eye

Optic Chasm- place at base of the brain where some fibers from the optic nerve cross to the other side of the brain.

Step 4: In the Brain

Visual cortex located in the occipital lobe

VC receives impulses from cells of the retina that activate feature detectors

Dr. Huble and Dr. Weisel: groups of neurons in the VC respond to different types of visual images

VC has feature detectors for vertical lines, curves, and motion

Our visual perception is a combination

Trichromatic Theory

Three types of cones:




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

Does not explain afterimages or color blindness well.

Opponent-process Theory

Either/or response of the three color receptors

Sensory receptors organized in pairs

(red/green, yellow/blue, black/white)

If red is stimulated, green won’t fire.

Explains the color after images and color blindness

Combination of Theories

A combination of both explains color vision completely

Colorblindness- partial or total inability to perceive hues

Trichromats- have normal color vision

Monochromats- totally colorblind

Dichromats- blind to red/green or blue/yellow

Audition Basics

Stimulus/input is sound waves

Ears contain structures for hearing and balance

Amplitude- height of a sound wave that determines loudness- measured in decibles


Number of complete waves per unit of time

Dogs can hear sounds at higher frequencies than humans can

Hertz (Hz)- cycles per second= measue of the frequency of waves

More hearing basics

Pitch- auditory experience corresponding primarily to frequency of sound vibrations resulting in higher or lower tones.

Decibel- the magnitude of a wave- determines loudness.

Parts of the Ear

Ear canal- aka auditory canal

Eardrum- aka tympanic membrane

Hammer, anvil and stirrup- small bones in the inner ear relay eardrum to the inner ear

Cochlea- contains fluid that vibrates causing the basilar membrane to vibrate

Basilar membrane- inside the cochlea- contains sense receptors for sound

Organ of Corti- Contains receptor cells

Auditory nerve- bundle of neurons that carries signals from the ears to the brain.

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


In basilar membrane there are hair cells.

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


Sent then to thalamus up auditory nerve.

Pitch Theories

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.

More focused on the lower tones.

Deafness/Hearing Loss

Conductive- sound vibrations from tympanic membrane are blocked (wax, fluid build-up, infection, abnormal bones growth) REPLACE THE


Sensorineural – damage to auditory nerve (head injury, birth defects, LOUD NOISES, high BP)



Prebycusis- changes in the inner ear- common in old age

Tinnitus- constant ringing or roaring sound.

Cause may not be found.


When skin is indented, pierced, or experiences a change in temperature the sense of touch is activated.

Pain: Gate control theory

Spinal cord has a neural “gate” to block or allow pain signals to the brain


 Pain tells the body that something has gone wrong.

Usually pain results from damage to the skin and other tissues. A rare disease exists in which the afflicted person feels no pain.: CIPA

Taste is a Chemical Sense

Taste buds papillae-bumps on your tongue

We sense four tastes: sweet, salty sour, and bitter

All others are a combination of the basic 4

Umami recently discovered comes from glutamate (like MSG)

Different parts of the tongue detect all types

Smell is a Chemical Sense



Smell the nose and brain work together to “smell”

Chemical molecules enter the nose, dissolve in mucous within a membrane called the olfactory epithelium that contains receptor cells sensitive to odors. Located about 7 cm up the nose in the nostrils

Pheromone– chemical the communicates info to others through smell

Smell and Memory

Why do some smells trigger memories???

Where are memories primarily stored?

sensory interaction

When one sense affects another sense, sensory interaction takes place. So, the taste of strawberry interacts with its smell and its texture on the tongue to produce flavor.

Other “Senses”


tells us about how the body is oriented in space

Responsible for balance

(head and body’s position)

Semicircular canals- located in the inner ear sensitive to body rotation

Vestibular Sacs- inner ear responsible for sensing gravitation, forward, backward and vertical movements


System for sensing position and movement of individual body parts

Senses of force and movement

 of muscles

Stretch receptors- sense muscle strength and contractions


Absolute Threshold

•The minimum stimulation necessary for a person to detect a particular stimulus 50% of the time. (see table for examples) AKA Detection

Sub Threshold = BELOW the minimal stimulus needed… AKA Subliminal messages

Difference Threshold

AKA: Just Noticeable Difference (JND)

The smallest amount of change that a person can detect between two stimuli 50% of the time.

Absolute Threshold vs. Difference Threshold

If you put your hand on a burner and turned it on, the first time you felt something would be Absolute Threshold and the second you noticed it getting hotter would be Difference Threshold.

Weber’s Law

Weber’s Law – detection of a stimulus depends on the original stimulus itself.

Example: If a 300 lb. person loses 20 lbs and a 120 lb. Person loses 20 lbs, which one would you notice lost the weight first?

(120 lbs because 20 lbs is a larger % of their body weight)

AKA- Difference Threshold

Signal Detection Theory

Investigates effects of distractions and interference on perceptions. Detection depends on:

1. Stimulus variables (how weak or strong the stimulus is)

2. Environmental variables (what’s going on around you)

3. Organismic variables (Your own experience, expectations, motivation and alertness)

Selective Attention

Focusing conscious awareness on a particular stimulus to the exclusion of others

The ability to focus on one stimulus at a time

Allows a person to function in a world filled with many stimuli

People with ADD have trouble doing this.


Selective Attention


Perceptions about objects change from moment to moment. We can perceive different forms of the

Necker cube; however, we can only pay attention to one aspect of the object at a time.

Necker Cube

Perceptual Organization

Gestalt Rules


 When vision competes with our other senses, vision usually wins – a phenomena called visual capture.

How do we form meaningful perceptions from sensory information?

We organize it. Gestalt psychologists showed that a figure formed a “whole” different than its surroundings.

More Gestalt Rules


Form Perception- figure ground

Proximity- close objects are perceived as being in the same group

Similarity- objects that look similar are perceived to be in the same group

Continuity- continuous forms are perceived as the same group.

Closure- Closing in gaps on familiar objects

Similar to top down processing

Depth Perception


Depth perception enables us to judge distances.

Gibson and Walk (1960) suggested that human infants (crawling age) have depth perception. Even newborn animals show depth perception.

Visual Cliff

Perceptual Adaptation

Visual ability to adjust to an artificially displaced visual field, e.g., prism glasses .


Binocular Depth Cues (both eyes required)

Retinal Disparity

Stereoscopic Vision

Distance cue based on the difference between the images

Eyes don’t perceive the exact same image

(peripheral vision)

Combining two retinal images to give a 3-dimensional perception.

Overlap in the center- the brain connects them into one image

Convergence: Neuromuscular cues. When two eyes move inward (towards the nose) to see near objects and outward (away from the nose) to see faraway objects.

Monocular Depth Cues –Visual cues requiring use of one eye


Linear Perspective

Relative Size

Monocular Cues

Texture Gradient: Indistinct (fine) texture signals an increasing distance- Course objects appear to be closer.

Shadowing- areas in shadows appear farther away

Relative Clarity (Ariel Perspective) the further away the less clear object appear to be

Motion Perception: Objects traveling towards us grow in size and those moving away shrink in size. The same is true when the observer moves to or from an object.


Relative Motion

In this example, the passenger is moving past a stable world. If she fixes her gaze on the bridge, objects behind it will appear to move forward. The farther away the object is, the more slowly it will appear to move. Objects in front of the fixation point appear to move backward.

Apparent Motion

Phi Phenomenon: When lights flash at a certain speed they tend to present illusions of motion.

Neon signs use this principle to create motion perception.


Perceptual Constancy


Perceiving objects as unchanging even as illumination and retinal images change. Perceptual constancies include constancies of shape and size.

Shape Constancy

Don’t forget :

Color Constancy



Size-Distance Relationship

The distant monster (below, left) and the top red bar (below, right) appear bigger because of distance cues.


Size-Distance Relationship

Both girls in the room are of similar height.

However, we perceive them to be of different heights as they stand in the two corners of the room.


Both photos from S. Schwartzenberg/ The Exploratorium

Ames Room


The Ames room is designed to demonstrate the sizedistance illusion.

Perceptual Interpretation

Immanuel Kant (1724-1804) maintained that knowledge comes from our inborn ways of organizing sensory experiences.


John Locke (1632-1704) argued that we learn to perceive the world through our experiences.

How important is experience in shaping our perceptual interpretation?

Sensory Deprivation


Blakemore & Cooper (1970)

Kittens raised without exposure to horizontal lines later had difficulty perceiving horizontal bars.

Perceptual Set

Our experiences, learned assumptions and beliefs shape our experiences


Streetcar scene of a black man talking to a white woman. He is holding a knife.

The subjects tell the story (like telephone) to another person.

The typical story told by the last person included the black man holding the knifecentral theme in many trials.

Three perceptual distortions

Leveling- the perceiver DROPS certain details because they don’t fit his/her cognitive categories or assumptions.

Sharpening- details of the story that are consistent with the values and interests of the perceiver are emphasized

Assimilation- padding and organizing are used to make the central theme fit expectations


All what we perceive not only comes from the environment but also from our minds. Schemas or concepts develop through experience

Assimilation vs Accommodation

Perception & Human Factors

Human Factor Psychologists design machines that assist our natural perceptions.

The knobs for the stove burners on the right are easier to understand than those on the left.


Can there be perception without input?

Most would say no.

Scientists tend to agree

What about ESP (Extrasensory