Sensation and Perception

Sensation: your window to the world

Perception: interpreting what comes in your window.

Sensations and Perceptions

Sensations - the passive process of bringing information from the outside world into the body and to the brain.

Perception - the active process of selecting, organizing, and interpreting the information brought to the brain by the senses

What is Sensation?

A stimulus can be measured in a variety of ways including it’s size, duration, intensity, or wavelength.

A Sensation occurs anytime a stimulus activates one of your receptors.

The sense organs then detect any change in energy, such as light, heat, sound, and physical pressure.

What is Sensation?

Sensation occurs when special receptors in the sense organs—the eyes, ears, nose, skin, and taste buds—are activated, allowing various forms of outside stimuli to become neural signals in the brain. (This process of converting outside stimuli, such as light, into neural activity is called transduction.)

Sensory systems

Transduction - Communication between the brain & the rest of the body occurs via neuron. Information goes from the senses to the thalamus , then to the various areas in the brain.

All senses involve something called receptor cells. Their job is to transduce (transform or even “translate”) physical stimulation/physical energy from the environment into electrochemical messages that can be understood by the brain.

Psychophysics

This explains how sensation and perception are related

Psychophysics: The study of the relationships between sensory experiences and the physical stimuli that cause them!

So where do vision and hearing (& the other senses) happen?The Brain! The physical energy in the

environment is detected by the eyes, ears, etc. but we can’t see, hear, etc. until the brain interprets them—i.e., makes sense of them. So in a way, we see, hear, smell, etc. in our brains!

Absolute Threshold

The Absolute Threshold is the level of stimulus that produces a positive response of detection 50% of the time.

the lowest level of stimulation that a person can consciously detect 50 percent of the time the stimulation is present.

The Absolute Thresholds for the “5” senses in humans are the following:

1. Vision: Seeing a candle flame 30 miles away on a clear night.

2. Hearing: Hearing a watch ticking 20 feet away. 3. Taste: Tasting 1 teaspoon of sugar dissolved

into 2 gallons of water. 4. Smell: Smelling one drop of perfume in a 3

room house. 5. Touch: Feeling a bee’s wing falling a distance

of one centimeter onto your cheek.

Weber’s law of Weber’s law of just noticeable just noticeable differences (jnd, differences (jnd, or the or the difference difference

thresholdthreshold). ).

• The difference threshold is the amount of change needed for us to recognize that a change has occurred. 

• It’s the smallest difference between two stimuli that is detectable 50 percent of the time

• Weber's Law states that “The larger or stronger the stimulus, the larger the change required for a person to notice that anything has happened to it.”

ExampleExample • Imagine holding a five pound weight and

one pound was added.  Most of us would notice this difference.  But what if we were holding a fifty pound weight?  Would we notice if another pound were added?  The reason many of us would not is because the change required to detect a difference has to represent a percentage.  In the first scenario, one pound would increase the weight by 20%, in the second, that same weight would add only an additional 2%. 

Sensory Adaptation

Adaptation (sometimes called habituation) is a part of everyday experience. It’s a decreased responsiveness to stimuli due to constant stimulation.

We are able to respond to the changes in our environment because our senses have the ability to adapt, or adjust themselves, to a constant level of stimulation.

Once your senses get used to a new level of a stimulation, they respond only to deviations from it.

Examples of Adaptation 1. Your eyes eventually adjust to a

darkened movie theatre. At first you see blackness, but eventually, you can see what is going on around you.

2. When you first jump into a pool that “feels cold” your body reacts to the stimulus. Eventually, your body adapts to the sensation and you become “comfortable.”

3. When you first walk into a sports locker room, the smell is almost nauseating. After a while, your senses adjust and you can hardly tell.

Visual SensationVisual Sensation

• Vision is the most studied of all of the senses! Our most dominating sense.

• There are many parts of an eye but the basic ones are the cornea, iris, retina, optic nerve and pupil.

• Our eye is stimulated by various wavelengths of light. The different wavelengths are responsible for the diversity of colors we see. There are many other types of waves that our eye cannot detect.

• Light is electromagnetic radiation that travels in the form of waves. Light is emitted from the sun, stars, fire, and lightbulbs. Most other objects just reflect light.

People experience light as having three features: color, brightness, and saturation. The color or hue of light depends on its wavelength, the distance between the peaks of its waves.

• The brightness of light is related to intensity or the amount of light an object emits or reflects. Brightness depends on light wave amplitude, the height of light waves. Brightness is also somewhat influenced by wavelength. Yellow light tends to look brighter than reds or blues.

• Saturation or colorfulness depends on light complexity, the range of wavelengths in light. The color of a single wavelength is pure spectral color. Such lights are called fully saturated. Outside a laboratory, light is rarely pure or of a single wavelength. Light is usually a mixture of several different wavelengths. The greater number of spectral colors in a light, the lower the saturation. Light of mixed wavelengths looks duller or paler than pure light.

• Wavelength ——> ColorAmplitude ——> BrightnessComplexity ——> Saturation

The Human EyeThe Human Eye

How does vision occur?How does vision occur?• 1. Light waves enter the eye through the cornea, a

transparent protective structure at the front of the eye. Behind the cornea is the pupil, The opening in the iris that regulates the amount of light entering the eye.

• 2. Light then reaches the lens: A flexible, elastic, transparent, structure in the eye that changes its shape to focus light on the retina.

• 3. Light then hits the retina: The innermost coating of the back of the eye, containing the light-sensitive receptor cells. The fovea is the most sensitive area of the retina because it has the greatest concentration of cones. Rods and cones are the photoreceptors.

• 4. This light energy is then turned into “neuronal impulses,” which are sent down the optic nerve: The nerve that carries impulses from the retina to the brain.

Sensory Receptor CellsSensory Receptor Cells• There are two types of sensory receptor

cells which are located on the retina– Rods– Cones

• Rods enable us to see black and white, are more sensitive to light, and there are 100 million in each eye

• Cones enable us to see color, they work best in bright light, there are 6.5 million in each eye and they are located mostly at the center of the eye

Sensory Receptor CellsSensory Receptor Cells• These cells transform light energy into

neural impulses that are sent to various areas in the brain through the bundle of neurons called the optic nerve.

• What is the place called in which the optic nerve leaves the eye?– The blind spot

• Why is it called “the blind spot”?– Because there are no rods & cones on this area

(there are neurons instead), images that fall on this area of the retina are not “seen”!

Light/Brightness and Dark Light/Brightness and Dark AdaptationAdaptation

• Dark adaptation occurs as the eye recovers its ability to see when going from a brightly lit state to a dark state. (The light-sensitive pigments that allow us to see are able to regenerate or “recharge” in the dark.) The brighter the light was, the longer it takes the rods to adapt to the new lower levels of light

• When going from a darkened room to one that is brightly lit, the opposite process occurs. The cones have to adapt to the increased level of light, and they accomplish this light adaptation much more quickly than the rods adapt to darkness—it takes a few seconds at most (Hood, 1998).

Common Visual defectsCommon Visual defects• Hyperopia/

farsightedness• Presbyopia• Myopia/

nearsightedness• Astigmatism• Tunnel vision• Diplopia• Scotoma

• Color blindness- Totally color blind- Partially color blind

Auditory/Hearing SensationAuditory/Hearing Sensation

HearingHearing• Hearing depends on vibrations in the air

called sound waves.• Sound waves from the air pass through

various bones until they reach the inner ear, which contains tiny hair like cells that move back and forth.

• These hair cells change sound vibrations into neuronal signals that travel through the auditory nerve to the brain.

We hear sound WAVESWe 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.

Three parts: Three parts: • External or outer ear – Function: Gathering sound

energy and amplification of sound pressure. -pinna, external meatus, eardrum/tympanic

membrane• Middle ear Function: Transmission of acoustic

energy from air to the cochlea. - Hammer, anvil, stirrup • Inner ear Function: Transformation of mechanical

waves (sound) into electric signals (neural signals).

– vestibular portion, cochlea, basilar membrane

Transduction in the earTransduction 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!!!

Auditory defectsAuditory defects =Deafness =Deafness• There are 2 types of deafness:

– 1. Conduction Deafness: occurs when anything hinders physical motion through the outer or middle ear or when the bones of the middle ear become rigid and cannot carry sounds inward. (Can be helped with a conventional hearing aid.)

– 2. Sensorineural Deafness: Occurs from damage to the Cochlea, the hair cells, or the auditory neurons. (Complete Sensorineural deafness cannot be helped by a hearing aid.)

Olfactory/Smelling SensationOlfactory/Smelling Sensation

Olfactory/Smelling Olfactory/Smelling SensationSensation

• Smell depends on sensory receptors that respond to airborne chemicals.

• In humans, these chemoreceptors are located in the olfactory epithelium — a patch of tissue about the size of a postage stamp located high in the nasal cavity. The olfactory epithelium is made up of three kinds of cells:

-sensory neurons each with a primary cilium -supporting cells between them -basal cells that divide regularly producing a fresh

crop of sensory neurons to replace those that die

Some classifications of odorSome classifications of odor• Camphoric –

Mothballs• Musky – Perfume • Roses – Floral• Pepperminty - Mint

Gum• Etheral - Dry

Cleaning Fluid

• Pungent - Vinegar• Putrid - Rotten

Eggs• Fruity – oranges• Spicy – spices• Smoky – anything

burning

Disorders of olfaction:Disorders of olfaction:

• Anosmia – inability to smell • Cacosmia – things smell like feces• Dysosmia – things smell different than they

should • Hyperosmia – an abnormally acute sense of smell. • Hyposmia – decreased ability to smell • Olfactory Reference Syndrome – psychological

disorder which causes the patient to imagine he or she has strong body odor

• Parosmia – things smell worse than they should • Phantosmia – "hallucinated smell," often

unpleasant in nature

Gustatory/Taste SensationGustatory/Taste Sensation• Gustation - The sensation of taste

– We have bumps on our tongue called papillae.– Taste buds are located on the papillae (they are actually

all over the mouth).

• Your tongue and the roof of your mouth are covered with thousands of tiny taste buds. When you eat something, the saliva in your mouth helps break down your food. This causes the receptor cells located in your tastes buds to send messages through sensory nerves to your brain. Your brain then tells you what flavors you are tasting.

Taste SensationTaste Sensation

Gustatory/Taste SensationGustatory/Taste Sensation• Five basic tastes

– Sweet – Sour– Salty– Bitter– Umami

Sense of touch/Cutaneous or Sense of touch/Cutaneous or skin sensation skin sensation

• Skin - The largest organ of your body– Performs many important biological functions while also

providing much of what is known as sensual pleasure • Our sense of touch is controlled by a huge network of

nerve endings and touch receptors in the skin known as the somatosensory system. This system is responsible for all the sensations we feel - cold, hot, smooth, rough, pressure, tickle, itch, pain, vibrations, and more.

3 layers:– Epidermis - outer layer– Dermis - intermediate layer– Deep layers of subcutaneous adipose tissue

Sensory functionsSensory functions• Factual

experiences – pressure and pain

• Thermal experiences – warmth and cold

Pain Pain • Pain receptors are probably the most important

for your safety because they can protect you by warning your brain that your body is hurt!

• Pain– Motivates us to tend to injuries, to restrict activity, and

to seek medical help– Teaches us to avoid pain-producing circumstances in the

future• Chronic pain

– Pain that persists for three months or more– Three common types

• Low-back• Headache• Arthritis

Skin SensesSkin Senses

• Melzack and Wall– Gate-control theory

• Contend that there is an area in the spinal cord that can act like a “gate” and either inhibit pain messages or transmit them to the brain

• You feel pain when pain messages carried by the small, slow-conducting nerve fibers reach the gate and cause it to open

• Contend that messages from the brain to the spinal cord can inhibit the transmission of pain messages at the spinal gate and thereby affect the perception of pain