chapter 4 sensation. basic principles of sensation sensation is the process that detects stimulation...

Chapter 4Sensation

Basic Principles of Sensation

Sensation is the process that detects stimulation from our bodies and our environment.


Perception is the process that organizes those stimuli into meaningful objects and events and interprets them.


Psychophysics is the study of how physical stimuli are translated into psychological experience.

Physical Properties of Waves

Short wavelength=high frequency(bluish colors, high-pitched sounds)

Long wavelength=low frequency(reddish colors, low-pitched sounds)

Great amplitude(bright colors, loud sounds)

Small amplitude(dull colors, soft sounds)

Color and Wavelength of Light

An object appears as a particular color because it absorbs certain wavelengths of light and reflects others.

These wavelengths are simply energy; colors are

created by our nervous system in response to them.

Species differ in what they see when looking at the same object.

Our difference threshold for colors is so low that the average person can discriminate about 2 million different colors.

Sensory Information Must Be

Converted into Neural Impulses

Sound, light, etc. cannot travel through our nerves to the brain.

Sensory organs convert their physical properties into neural impulses.

This conversion process is called transduction.

Sensory Information Must Be

Converted into Neural Impulses

Transduction takes place at sensory receptors. Next, connecting neurons in the sense

organs send this information to the brain. The brain processes these neural impulses

into what we experience. Some stimuli are just as real as those that

we can transduce, but they are not a part of our sensory experience.

Sensation

Sensory receptors: specialized forms of neurons; the cells that make up the nervous system

LO 3.1 Sensation and How It Enters the Central Nervous System

Sensation

Sense Organs: eyes ears nose skin taste buds


Our Senses Vary in Their Sensitivity Thresholds

Signal-detection theory contends that detection of a stimulus is influenced by observers’ expectations.

How likely is the stimulus to occur? How important or rewarding is detecting it?

So absolute threshold may vary.

It is usually defined as the intensity of a stimulus that can be detected 50% of the time.


Absolute threshold: the lowest level of intensity of a given stimulus that a person can detect half the time

As people age, their absolute thresholds for all senses increase.

Sensation--Thresholds When stimuli are

detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”

0

25

50

75

100

Low Absolutethreshold

Medium

Intensity of stimulus

Percentageof correctdetections

Subliminal stimuli

Subliminal stimuli

Subliminal stimuli: stimuli that are below the level of conscious awareness just strong enough to activate the sensory

receptors, but not strong enough for people to be consciously aware of them

limin: “threshold” sublimin: “below the threshold” supraliminal: “above the threshold”


Difference threshold is the smallest difference between two stimuli that is detected half (50%) of the time.

It is also called the “just-noticeable difference” or jnd.

Our Sensory Receptors Adapt to Unchanging Stimuli

Sensory adaptation: the tendency for our sensory receptors to have decreasing responsiveness to stimuli that continue without change.

Auditory adaptation occurs much more slowly than adaptation to odors, tastes, and skin sensations.

Habituation and Sensory Adaptation

Habituation: the tendency of the brain to stop attending to constant, unchanging information

Sensory adaptation: the tendency of sensory receptor cells to become less responsive to a stimulus that is unchanging


Habituation and Sensory Adaptation

Microsaccades: constant movement of the eyes; tiny little vibrations that people do not notice consciously; prevents sensory adaptation to visual stimuli


Sensory Adaptation

Vision

We See Only a Narrow Band of Electromagnetic Radiation

Wavelengths of visible light range from 400 to 750 nanometers.

Shorter wavelengths are experienced as violet. Intermediate ones as blue, green, and yellow. Longer ones as red.

Other forms of electromagnetic energy that our eyes cannot detect are:

Radio Infrared Ultraviolet X-ray radiation

Vision Spectrum of Electromagnetic Energy

Major Structures of the Human Eye

Structure of the Eye

Retina: final stop for light in the eye contains three layers:

ganglion cells bipolar cells photoreceptors that respond to various

light waves

LO 3.2 What Is Light?


Rods: visual sensory receptors found at the back of the retina; responsible for noncolor sensitivity to low levels of light

Cones: visual sensory receptors found at the back of the retina; responsible for color vision and sharpness of vision


Photoreceptors in the Retina

Rods (125 million)Located at the edges of the retina.Are not involved in color vision.

Function best under low-light conditions.

Cones (7 million)Located near the center of the

retina (the fovea).Require bright light to be activated.Play a key role in color vision.

Vision--ReceptorsReceptors in the Human Eye

Cones Rods

Number

Location in retina

Sensitivity in dim light

Color sensitive? Yes

Low

Center

6 million

No

High

Periphery

120 million


Blind spot: area in the retina where the axons of the three layers of retinal cells exit the eye to form the optic nerve; insensitive to light


Retina’s Reaction to Light

Audition (Hearing)

Sound Is the Stimulus for Hearing

Soundwaves (pressure) are created when an object vibrates. Wave speed or frequency corresponds

to pitch. Amplitude (wave height) corresponds

to loudness of a sound. Most sounds are a combination of

many different waves of different frequencies. This sound complexity is caled timbre.

Auditory System: Three major parts of the Ear

Outer ear: The pinna is the most visible part of the outer

ear. The auditory canal is funnel shaped. The eardrum is at the end of the auditory

canal and it vibrates in sequence with sound waves.

Audition- The Ear


Middle ear: The ossicles are three tiny

interconnected bones—the hammer, anvil, and stirrup —that move and amplify sound waves before sending them to the inner ear.


Inner Ear innermost part of ear, containing

the cochlea, semicircular canals and vestibular sacs

Cochlea coiled, bony, fluid-filled tube in the

inner ear through which sound waves trigger nerve impulses

Sound Localization

Sound localization: the ability to locate objects in space solely on the basis of the sounds they make

Because the ears are only 6 inches apart, the time lag between the sound reaching both ears is very short.

Even such small time lags provide the auditory system with sufficient information to locate the sound.

Soundwaves

Sound Waves and DecibelsA typical sound wave. The higher the wave, the louder the sound; the lower the wave, the softer the sound. If the waves are close together in time (high frequency), the pitch will be perceived as a high pitch. Waves that are farther apart (low frequency) will be perceived as having a lower pitch.

Soundwaves

Sound Waves and Decibels

A decibel is a unit of measure for loudness.

See the next two slides for decibels of various stimuli.

The Intensity of Some Common Sounds

Smell and Taste: The Chemical Senses

Olfaction: the sense of smell

The stimuli are airborne molecules

Olfactory receptor cells are at the top of the nasal cavity.

These cells transmit information to the olfactory bulb at the base of the brain.

The olfactory bulb processes this information and sends it to the primary olfactory cortex.

Smell (Olfaction)

Olfaction (Olfactory Sense) sense of smell

Olfactory Bulbs areas of the brain located just above the

sinus cavity and just below the frontal lobes that receive information from the olfactory receptor cells

There are at least 1,000 olfactory receptors.

LO 3.6

How Work

The Olfactory Receptors A cross section of the nose and mouth. This drawing shows the nerve fibers inside the nasal cavity that carry information about smell directly to the olfactory bulb just under the frontal lobe of the brain (shown in green).

The Olfactory Receptors(b) A diagram of the cells in the nose that process smell. The olfactory bulb is on top. Notice the cilia, tiny hairlike cells that project into the nasal cavity. These are the receptors for the sense of smell.

Smell (Olfaction)

Olfaction

Olfactory sensitivity is determined by the number of receptors in the epithelium.

Odors can evoke memories and feelings associated with past events.

Gustation: the sense of taste

Gustation occurs when a substance makes contact with special receptor cells in the mouth, called taste buds.

Most taste buds are located on the tongue, but some are in the throat and on the roof of the mouth.

Taste

Taste buds taste receptor cells in mouth;

responsible for sense of taste Gustation

the sensation of a taste

LO 3.6 How Senses of Taste and Smell Work

The right side of this drawing shows the nerves in the tongue’s deep tissue.

The right

The right side of this drawing shows the nerves in the tongue’s deep tissue.

Microphotograph of the surface of the tongue, showing two different sizes of papillae. The taste buds are located under the surface of the larger red papillae, whereas the smaller and more numerous papillae form a touch-sensitive rough surface that helps in chewing and moving food around the mouth.

Taste

Five Basic Tastes: sweet sour salty bitter “brothy,” or umami

LO 3.6 How Senses of Taste and Smell Work

Gustation: the sense of taste

When taste cells absorb chemicals

dissolved in saliva, they trigger neural impulses, transmitted to one of two brain areas:

First: information first sent to the thalamus and then to the primary gustatory cortex, where taste identification occurs

Second: information sent to the limbic system, which allows a quick response to a taste prior to conscious identification of it (example, spitting out sour milk)

The Five Primary TastesNot all researchers agree on this.

Somasthetic (Bodily) Senses

The Skin Senses Pressure, Temperature, & Pain

Our skin is our largest sensory organ. Sense of touch is actually a

combination of three skin senses:

Pressure: physical pressure on the skin

Temperature: The skin contains two kinds of temperature receptors, one sensitive to warm and the other to cold.

Pain: The Body’s Warning

System Pain is induced through tissue damage or intense

stimulation of sensory receptors.

Gate-control theory proposes that small-diameter nerve fibers (S-fibers) and large-diameter nerve fibers (L-fibers) open and close “gateways” for pain in the spinal cord.

Pain gateways can be closed—thus preventing pain messages from reaching the brain—by a class of substances known as endorphins.

Cross Section of the Skin and Its Receptors

The skin is composed of several types of cells that process pain, pressure, and temperature. Some of these cells are wrapped around the ends of the hairs on the skin and are sensitive to touch on the hair itself, whereas others are located near the surface, and still others just under the top layer of tissue.

Somasthetic Senses Vestibular senses: the sensations of

movement, balance, and body position; provide information on the position of the body in space by sensing gravity and motion (inner ear).

Sensory conflict theory: an explanation of motion sickness in which the information from the eyes conflicts with the information from the vestibular senses, resulting in dizziness, nausea, and other physical discomforts

LO 3.7 Sense of Touch, Pain, Motion, and Balance

The Proprioceptive Senses: Body Movement and Location

Kinesthetic sense: provides information about the movement and location of body parts with respect to one another

This information comes from proprioceptors (receptors in muscles, joints, and ligaments.)

chapter 4 sensation. basic principles of sensation sensation is the process that detects stimulation...

Documents

sensory organs

physical stimuli

sensory information

sensory experience

thresholdswhen stimuli

threshold sublimin

ones absolute threshold

sensationsensory receptors