Sensation and Perception

Sensation – the process of detecting physical energy and transforming it into neural signals – This transformation process is called transduction Perception – selecting, organizing, and interpreting sensations Do we see the world as it actually is? – Nope. The world we see is a construct of our minds. There is no color. There is no sound.

Bottom up processing – Sensation to perception. Body to brain.

What is the smallest amount of something you can sense? Absolute threshold – the minimum amount of stimulation you can detect 50% of the time Try it.. Some common absolute thresholds include:

Why “50% of the time?” Signal Detection Theory – our ability to sense things is influenced by our: – Experience – some people are trained to detect specific things (police officers) – Expectations – you may/may not be ready (clowns) – Motivation – you may/may not care – Level of fatigue/alertness – you might be tired

Subliminal messages Can we be influenced by things below our absolute threshold? Can we be manipulated through subliminal messages? Yes and no They may have a brief effect – Priming Studies have shown that subliminal messages do not produce a lasting outcome

A_ _OM_BI_E

How much does a stimulus have to change before we notice a difference? For example, how bright does a light need to be before we can tell it is brighter? How much does a sound need to change before we can tell it is louder? Difference Threshold/Just Noticeable Difference (JND)- minimum difference between two stimuli required for detection 50% of the time

A quick experiment..

Weber’s Law – to be perceived as different, two stimuli must differ by a constant minimum percentage In other words, it’s not the amount of stimuli that matters, it’s the percentage; it’s the ratio of the second stimulus to the first Light intensity – 8% Weight – 2% Tone frequency -.3%

Other examples Suit and sweater, which first? New cars

Sensory Adaptation Diminished sensitivity as a result of constant stimulation Do you notice the chair pressing against your legs? If you put a band aide on, very soon you won’t notice it So then if you stare at something, shouldn’t it disappear as the sense receptors in your eye become used to it?

Yes It should.. It would.. But… Your eyes are always moving, even when you stare Try this…

Phototransduction Conversion of light energy into neural signals the brain can understand

Light and color Light can behave as a wave or a particle Wavelength – the distance from the peak of one wave to the peak of the next

Hue (color) – dimension determined by the wavelength of light

Wavelength (Hue) Different wavelengths of light result in different colors. 400 nm 700 nm Long wavelengths Short wavelengths Violet IndigoBlue Green Yellow OrangeRed

Intensity – amount of energy in a wave, determined by amplitude (i.e. how “bright” a light is)

Intensity (Brightness) Blue color with varying levels of intensity. As intensity increases or decreases, blue color looks more “washed out” or “darkened.”

The spectrum of electromagnetic energy

Parts of the Eye Cornea – outer covering Pupil – adjustable opening in center of eye Iris – muscle that controls the pupil Lens- transparent structure behind the iris that changes shape to focus images Retina – inner surface of the eye. Contains receptor rods and cones, and a bunch of other neurons (bi-polor, ganglion cells)

 Rods  peripheral retina  detect black, white and gray  twilight or low light  Cones  near center of retina  fine detail and color vision  daylight or well-lit conditions

Rods Cones

Nearsightedness – nearby objects are seen more clearly Farsightedness – faraway objects are seen more clearly

Optic nerve- carries neural impulses from the eye to the brain Fovea- central point in the retina, where the eye’s cones cluster Blind spot See if you can find your blind spot..

Processing visual information

Feature Detection

Parallel processing – processing several aspects of a problem simultaneously Blindsight – seeing without seeing. Huh?

Color Vision Trichromatic theory (Young-Helmholtz) – since any color can be created by combinations of red, blue, and green, the eye must have three types of receptors for these three colors Subtractive- subtracts wavelengths from the reflected light Additive

Color blindness

8% of males show a color weakness, but only.05% of females Who’s better at discriminating color? Why?

Opponent-Processing theory Yellow is a mixture of red and green light, but people blind to red and green can often see yellow. How is this possible? Afterimages

After Images Stare at the eye of the red parrot while you slowly count to 20, then immediately look at one spot in the empty birdcage. The faint, ghostly image of a blue-green bird should appear in the cage.

Opponent Colors Gaze at the middle of the flag for about 30 Seconds. When it disappears, stare at the dot and report whether or not you see Britain's flag.

Complementary Afterimages

In the nervous system, color processing cells are grouped together like this: Red-green Blue-yellow Black-white When you stare at one color, you exhaust that receptor, so when you look at a white page, you see the opponent color

Opponent Process Theory Hering proposed that we process four primary colors combined in pairs of red-green, blue- yellow, and black-white. Cones Retinal Ganglion Cells

Color Constancy Color is relative The color you see depends on the context

Hearing (audition)

What causes sound? Molecules bump into each other at different rates, causing small changes in air pressure. Your brain converts these changes to neural impulses that interprets as sound Sound energy is measured in decibels Absolute threshold for hearing is 0 decibels, a loud thunder crack is dB

Parts of the ear Sound travels through your outer ear and causes your eardrum to vibrate these vibrations are then transferred to the middle ear where they cause three bones – called the hammer, the anvil, and the stirrup – to vibrate The vibrations cause the fluid in the cochlea to ripple These ripples bend tiny hair cells The hair cells send neural messages to the brain = hearing

Loudness is determined by the number of activated hair cells Pitch Place theory Frequency theory

How does the brain locate sounds?

Hearing loss Conduction hearing loss Nerve hearing loss Cochlear implants Sensory compensation

Sensory interaction

Touch Mixture of pressure, warmth, cold, and pain Only pressure has specific nerve receptors Touch localization

Pain A product of the body and the brain Gate control theory Sensitivity to pain People who feel no pain Pain control

Taste Chemical sense Taste buds o Regeneration Super tasters

Taste Traditionally, taste sensations consisted of sweet, salty, sour, and bitter tastes. Recently, receptors for a fifth taste have been discovered called “Umami”. Sweet Sour Salty BitterUmami (Fresh Chicken)

Taste Your sensitivity to taste will decline if you: o Smoke heavily o Consume large amounts of alcohol o Grow older

Taste Culture and taste preferences:

Smell Peaks in early adulthood and then declines (like the other senses) Chemical sense (receptor cells in nasal cavity) Not filtered by thalamus Smell and memories Who has the best sense of smell? Subliminal smells T-Shirt experiments

Women Men Age Group Number of correct answers Women and young adults have best sense of smell

Body Position Kinesthesis Vestibular sense