Sensation CHAPTER 4 LESSONS 4.1 Basic Principles of Sensation 4.2 Vision 4.3 Hearing and Your Other Senses

LESSON 4.1 Basic Principles of Sensation OBJECTIVES Explain the concepts of sensory thresholds and compare the different theories. Describe sensory adaptation.

Sensory Thresholds Sensation is the process that detects stimuli from your body and environment.

Table 4-1 The Stimuli and Sensory Receptors for Each Primary Sense Stimulus Sensory Receptors Vision Light waves Light-sensitive rods and cones in the retina of the eye Hearing Sound waves Pressure-sensitive hair cells in the cochlea of the inner ear Taste Molecules dissolved in fluid on the tongue Taste cells in the taste buds of the tongue Smell Molecules dissolved in fluid in the nose Sensitive ends of olfactory (smell) neurons Touch Pressure on the skin Sensitive ends of touch neurons

Absolute Threshold Psychophysics is the study of how physical stimuli are translated into psychological experience. Absolute threshold is the weakest amount of a given stimulus that a person can detect half of the time.

Table 4-2 Examples Of Absolute Thresholds Stimulus Absolute Threshold Vision A candle seen at 30 miles on a dark, clear night Hearing The tick of a watch at 20 feet under quiet conditions Taste One teaspoon of sugar in 2 gallons of water Smell One drop of perfume diffused into a three-room apartment Touch The wing of a fly falling on your cheek from a distance of 0.5 inch Source: Adapted from Galanter, 1962.

Signal-Detection Theory Signal-detection theory states that detecting a stimulus is influenced by a person’s decision-making strategy.

Difference Threshold Difference threshold is the smallest difference between two stimuli that can be detected half of the time. Weber’s law is the principle that to be noticed as different, two stimuli must differ by a constant minimum percentage rather than by a constant amount.

Sensory Adaptation Sensory adaptation is the tendency for sensory receptors to decrease in response to stimuli that continue at the same level.

Describe the way the brain perceives color. LESSON 4.2 Vision OBJECTIVES Identify and illustrate the structures of the eye that are responsible for vision. Describe the way the brain perceives color.

Figure 4-1 The Electromagnetic Spectrum

Structures of the Human Eye The pupil is an opening in the iris that allows light to enter the eye. The iris is a ring of muscles that range in color from light blue to dark brown. The lens is a clear, elastic, disc-shaped structure that refocuses light. The retina is the light-sensitive surface at the back of the eye. The optic nerve carries information from the retina to the brain. The blind spot is the area on the retina where the optic nerve leaves the eye and that contains no receptor cells.

Figure 4-2 Major Structures Of The Human Eye

Video Anatomy of the Eye (Virtual Reality) Videos are located on the Instructor’s Resource CD in the Videos folder. Filename: AnatomyEyeVR Running time: variable This video is activated by moving the mouse over the video screen to explore the anatomy of the eye.

Figure 4-3 How Light Travels through the Eye

Videos Transmission of Light through the Eye Videos are located on the Instructor’s Resource CD in the Videos folder. Filename: LightThroughEye Running time: 28 seconds

Color Vision All the colors you see are red, blue, and green, or a mixture of these three. The color is in your visual system. An object appears as a particular color because it absorbs or reflects certain wavelengths of light. Colors are created by the cones in your eye responding to wavelengths and sending neural signals to your brain, which then creates the colors you see.

Color Blindness Color blindness is a deficiency in the ability to distinguish among colors.

Figure 4-4 Test for Color Blindness

LESSON 4.3 Hearing and Your Other Senses OBJECTIVES Explain and illustrate the human auditory system and the structure of the ear. Describe the senses of smell, taste, touch, and body position and movement.

The Auditory System The auditory system controls your sense of hearing. Hearing begins with sound waves—vibrations in air, water, or solid material. The number of sound waves that pass through a given point in one second is called the sound’s frequency.

The Auditory System—Pitch When your sensory system experiences the physical sensation of frequency, you also have the psychological experience of pitch. High-pitched sounds are high frequencies Low-pitched sounds are low frequencies.

The Auditory System—Amplitude Loudness of sound is a psychological experience that corresponds to the height of a sound wave, called amplitude. Amplitude is measured in decibels (dB). The greater the amplitude, the higher the decibels, and the louder the sound.

Table 4-3 Decibel Level of Some Common Sounds Decibels Source Exposure Danger 180 Space shuttle launch Hearing loss certain within 150 feet of launch pad 140 Jet aircraft motor Any exposure dangerous 120 Sandblaster, thunderclap Immediate danger 100 Heavy auto traffic, lawn mower 2 hours 60 Normal conversation No danger 40 Quiet office 30 Quiet library 20 Soft whisper Minimal detectable sound

The Ear The ear is divided into three major parts: The outer ear is the part you see. The eardrum is a thin, flexible membrane that vibrates in sequence with sound waves. The cochlea is the coiled, fluid-filled tube in the inner ear that contains hair-like auditory receptors.

Figure 4-5 The Human Ear

Hearing Loss There are two types of hearing loss: Conduction hearing loss Sensorineural hearing loss

Conduction Hearing Loss Occurs when there are physical problems sending sound waves through the outer or middle ear Often involves a punctured eardrum or damage to any of the bones in the middle ear Hearing aids Common treatment for conduction hearing Tiny instruments worn just inside the outer ear Change sound waves into amplified vibrations and send them to the inner ear

Sensorineural Hearing Loss More common than conductive hearing loss Involves nerve problems in the inner ear Often occurs because hair cells in the cochlea are damaged either by disease, injury, or aging Cochlear implant Only means of restoring hearing Miniature electronic device surgically placed into cochlea Changes sound waves into electrical signals Best candidates—young children born with hearing loss

Smell Olfactory nerve transmits neural impulses containing smell information from the nose to the brain. The stimuli for smell are airborne molecules. These molecules enter your nasal passages and reach tiny receptor cells at the top of the nasal cavity. These receptor cells then transmit neural impulses containing smell information through the olfactory nerve to the brain. Once your brain has processed these neural signals, you experience the aroma or odor.

Figure 4-6 The Olfactory System

Taste Taste buds are sensory receptor organs that contain the receptor cells for taste. Taste occurs when receptor cells in your mouth and throat trigger neural impulses to the brain. About 50 to 150 of these receptor cells are contained in each of the 10,000 taste buds that are located mainly on the tongue.

Taste Sensations Four most familiar taste sensations: Sweetness (mostly sugars) Sourness (mostly acids) Saltiness (mostly salts) Bitterness (mainly chemicals that have no food value or are toxic) Most taste experiences are complex and result from the combined effects of receptor cells in the mouth and nose, which produce the different flavors you experience.

Figure 4-7 The Tongue Map Myth Myth: Different areas of the tongue are more sensitive to one of the four primary tastes. Fact: All your taste buds detect all taste qualities.

The Skin Senses Skin defines boundaries with the environment. Skin is your largest sensory organ. The sense of touch is actually a combination of three skin senses: Pressure Temperature Pain

Pressure The stimulus for pressure is physical pressure on the skin. The entire body is sensitive to pressure. Some areas have more receptors so are more sensitive.

Temperature Temperature sensations depend on which type of receptor is stimulated. Whether more warm or cold receptors are stimulated depends on the difference between your skin temperature and the temperature you are feeling.

Pain Pain serves as a warning system that signals danger and the risk of injury. Pain can also force people to cope appropriately with an injury. The most widely accepted theory of pain is gate-control theory. Gate-control theory describes how pain signals open a neurological “pain gate” in the spinal cord and how other touch signals close the gate.

Body Position and Movement Kinesthetic sense provides information about the movement and location of different parts of your body. Vestibular sense provides information on the position of your body by sensing gravity and motion. Equilibrium is another name for vestibular sense.

Chapter 4 Clicker Questions 1. Which refers to nerve cells firing less frequently after high levels of stimulation? a. critical thinking b. environmental threshold c. absolute threshold d. sensory adaptation

Chapter 4 Clicker Questions 2. The major contribution of the signal-detection theory was the establishment of specific absolute thresholds for all senses. a. True b. False

Chapter 4 Clicker Questions 3. Which is a ring of muscles that range in color from light blue to dark brown? a. pupil b. iris c. lens d. retina

Chapter 4 Clicker Questions 4. Loudness of a sound corresponds to the height of a sound wave called a. amplitude b. pitch c. frequency d. timbre

Chapter 4 Clicker Questions 5. What is the term for the senses that detect body position and movement? a. olfactory b. proprioceptive c. sensorineural d. auditory