Sensation and Perception

Chapter 4

Absolute Threshold – level of sensory stimulation necessary for sensation to occur◦ We do not pay attention to small sounds or

background noise if it is not important to us Sensation – process of receiving

information Perception – make it meaningful

Sensory Processes

Vision◦ Dominates the human senses◦ Lights starts out as white light and color is seen

only after the waves of white light hits objects and bounces back at us at different speeds or frequencies

Sensation

The Cornea and Iris ◦ The cornea is the shiny fluid in your eye

that covers your eye◦ The iris is a colored circular muscle that

opens and closes into larger or smaller circles to control the amount of light getting into the eye

Sensation

Lens◦ Focus objects you see onto the back of the

eye Pupil

◦ Light changes the size of your pupil◦ If you are disgusted your pupil will get smaller or

if you like something they will get larger◦ Pupils also open completely if someone is afraid

Sensation

Retina◦ When light that enters the eye gets to the back of

the eyeball it hits the retina Rods and Cones

◦ Rods are very sensitive to the violet-purple range of wave lengths

◦ Cones are used for color and daylight vision

Sensation

Color Defects◦ 8% of males and .5% of females have some

type of color blindness ◦ Truly “color blind” people are very rare◦ Animals have very elaborate rod and cones

systems Bulls get enraged by a red flag because of its color is

a myth

Sensation

Afterimages ◦ If you stare at a colored object for a minute the

chemicals in the cones for the colors you are seeing will be partially used up

◦ Afterimages occur from the remained unused cones

Sensation

Hearing Sound waves have a slower range of

speed than light waves Bats can find food at night by bouncing

sound waves off of them

Characteristics of Sound◦ Sounds vary in

pitch and intensity Intensity is

measured in decibels 130 Decibels and

beyond can become painful

Hearing

The Structure of the Ear◦ Ear size makes very little difference in what you

can hear◦ Sound waves are funneled in the ear

towards the eardrum When sound waves hit the drum it vibrates all

the way to the cochlea Key to hearing is in the cochlea by the cilia (hair like

extensions) Sends message to the auditory nerve in the brain

where the sound is interpreted

Hearing

Our skin contains three types of receptors◦ Pressure

Registers a pinprick, bruise, ant crawling up your arm◦ Changes in Temperature◦ Remains active continuously to record an

injury or poison Causes the painful feelings we have

Touch

Olfaction depends on the ability to detect chemicals

We come in second to animals in smelling Odors are hard to define using words but if

it is associated with an emotional event we never forget it

Smell Communication ◦ Smell is more important in eating than taste

Smell

Taste receptors operate by chemical communication

Mucus and Saliva cleanse the buds 4 Types of receptors

◦ Salt, Sweet, Sour, and Bitter

Taste

Salt ◦ Salt is necessary for survival ◦ Desire for salt gradually tapers off with age but

can reappear much later in life Sugar

◦ Vital for energy to run the body Sour and Bitterness

◦ Sourness detection serves as a protective function

◦ Food that has gone bad has a sour taste to it – but we usually smell it before we eat it

Taste

Perception is a matter of interpretation and expectation

Depth Perception◦ Visual Cliff Experiment

Experimenter was at the Grand Canyon and wondered if babies would crawl past the canyon rim

Lab – used a large table with retaining walls made of wood on the sides and a clear sheet of Plexiglas that made it appear there was a drop off

The mothers encouraged their children to go across the “drop” but the babies refused

Perception

Retinal Disparity ◦ Difference between the images received by

each of your retinas Example: Hold one finger in front of your face and

close one eye – now close the other What happened to your finger

Perception

Gestalt Psychologists used certain perceptual cues to make sense of items◦ Proximity – how close things are to one another◦ Closure – Fill in details that are not part of the

picture

Perception

Perception Illusions

◦ Occur when we perceive something inaccurately

◦ Come from the need for us to make sense of our surroundings

◦ Reversible Figure – The eye-brain mechanism keeps changing its mind