Sensation and Perception. 8.2 The Senses

Transcription

1 Sensation and Perception 8.2 The Senses

2 I. Introduction A. You probably think that you have just five senses: vision, hearing, taste, smell, and touch. In addition, people have two more internal senses: vestibular and kinesthetic. B. Each sense organ receives some sort of external stimulus, such as light, sound waves, or pressure. It then changes the sensation into a chemical-electrical message that the brain can understand.

3 I. Introduction (con t)

4 II. Vision A. The vision process begins when light enters the eye through the pupil and reaches the lenses. The lens changes shape to focus light on the retina. B. The retina is a coating at the back of the eye. It contains two types of lightsensitive cells called rods and cones. These cells change light impulses that the neurons carry over the optic nerve to the brain.

5 II. Vision (con t) C. Cones require more light than rods, they work best in daylight. Rods work in lower light and are more useful at night. There are many more rods than cones, but cones are sensitive to color. D. Colors we see are actually different wavelengths of light. We see color only after light waves hit objects and bounce back to us. We sense texture and solidity of objects by the speed at which the waves bounce back.

6 II. Vision (con t) E. When cones are not working well, a person cannot see color well. This condition is called color deficiency. F. Our vision system receives two images because we have two eyes. Instead of seeing double we see a combination of the images, this is called binocular fusion.

7 II. Vision (con t) G. Each eye projects a slightly different image on the retina. This difference is called retinal disparity. Example: Bring an object such as an eraser close to your eyes. Without moving it, look at the eraser first with one eye and then with the other. You will see the difference in the two images because of the different viewpoint each eye has. When you open both eyes, you will see no difference.

8 II. Vision (con t) H. Retinal disparity is important to your sense of depth. Your brain knows that a large difference between objects each eye brings in (retinal disparity) means the object is near. A small difference means the object is far away.

9 II. Vision (con t)

10 III. Hearing A. Hearing depends on sound waves, or vibrations in the air. Sound waves pass through several bones and fluids until the reach the inner ear. The inner ear contains tiny hairs that move back and forth changing vibrations into signals that neurons carry to the brain along the auditory nerve.

11 III. Hearing (con t) B. The amplitude, or height of sound waves, determines the loudness. Loudness is measured in decibels. C. The sound s pitch depends on the waves frequency, or rate of vibration. Low frequencies produce deep bass sounds, high frequencies produce squeaks.

12 III. Hearing (con t) D. Your ears work together to determine where a sound is coming from. Typically noise will be received louder in one ear than another telling the brain where the sound comes from. E. The outer ear directs sound waves down a short tube called the auditory canal.

13 III. Hearing (con t) F. The middle ear is made up of three small bones (the hammer, anvil, and stirrup) and filled with air. These bones are connected to the cochlea. G. The cochlea is the inner ear. The cochlea turns sounds into vibrations that create impulses that are carried to the brain.

14 III. Hearing (con t)

15 IV. Balance A. Your body s sense of balance comes from the vestibular system located in the inner ear. This system has three semicircular canals filled with fluid. When you move this fluid also moves sending stimuli to your brain to indicate spinning, falling, of tilting movements.

16 V. Smell and Taste A. Smell and taste are chemical senses. Inside your nose are smell receivers that send stimuli to the brain through the olfactory nerve. B. To taste something, molecules must stimulate taste buds on your tongue. The taste buds relay information to the brain regarding taste, temperature, and texture of the item being eaten.

17 V. Smell and Taste (con t) C. Four sensory experiences make up taste: sour, salty, bitter, and sweet. Much of what you taste is actually a result of your sense of smell. D. Sensations of warmth, cold, and pressure also affect taste.

18 VI. The Skin Senses A. Your skin provides at least four kinds of information to your brain: pressure, warmth, cold, and pain. B. The gate control theory of pain states that people can reduce their pain by shifting their attention away from it, or may send other signals to compete with the pain signals.

19 VII. The Body Senses A. Kinesthesis is the sense of movement and body position. It works with the vestibular system to control posture and balance. B. Receivers for kinesthesis are located near the muscles, tendons, and joints. C. Kinesthetic sensations help keep body movement coordinated.