18.3 Chapter 3: Sensation and Perception

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1. a. Perception
2. Signal detection theory states that various sensory factors and a person’s psychological state influence the ability to detect weak signals in the environment. Some things that may influence one’s ability to detect an intruder’s flashlight include the intensity of the light, level of alertness, the expectations about one’s role, and other interfering stimuli in the environment.
3. d. sensory adaptation.

1. wavelength
2. b. photoreceptors
3. The trichromatic theory of color vision suggests there are three types of cones, each sensitive to particular wavelengths in the red, green, and blue spectrums. The brain identifies a precise hue by calculating patterns of excitement among the three types of cones, that is, the relative activity of the three types.
   The opponent-process theory of color vision suggests that in addition to the color-sensitive cones, we also have neurons that respond to opponent colors (for example, red–green, blue–yellow). One neuron in an opponent pair fires when one is looking at red, for example, but is inactive when one is looking at green. Both the trichromatic and opponent-process theories clarify different aspects of color vision, as color perception occurs in the light-sensing cones in the retina and in the opponent cells serving the brain.
4. d. rods.

1. a. frequency
2. b. transduction.
3. place
4. Diagrams will vary. The pitch of a sound is determined by the frequency of its sound wave, which is usually measured in Hertz. Place theory suggests that the location of neural activity along the cochlea allows us to sense different pitches of high-frequency sounds. Frequency theory suggests that the pitch of a sound is determined by the vibrating frequency of the sound wave, basilar membrane, and associated neural impulses. Place theory explains our perception of pitches from 4,000 to 20,000 Hz, and frequency theory explains how we perceive the pitch of sounds from 20 to 400 Hz. The volley principle explains the perception of pitches from 400 to 4,000 Hz.

1. olfaction
2. b. transduction.
3. Smell, taste, and touch all include the sensing of information in the environment through receptor cells designed to detect a particular kind of stimuli. These three senses also involve transduction, which is the process of transforming stimuli into neural signals. Neural signals for all three of these senses then are processed by the central nervous system. Smell and taste are considered chemical senses, as they both involve sensing chemicals (odor molecules for olfaction, flavor molecules for taste) in the environment. Taste and touch relay data through the thalamus before going to higher brain centers, whereas olfaction is not relayed through the thalamus.
4. c. the gate-control theory

1. b. perceptual constancy
2. a. convergence
3. ESP is the purported ability to obtain information about the world in the absence of sensory stimuli. There is a lack of scientific evidence to support the existence of ESP, and most so-called evidence comes in the form of personal anecdotes. Subjective information can be biased. Using critical thinking, we must determine the credibility of the source and validity of the evidence. Despite ESP’s lack of scientific credibility, many people still believe in its existence in part because of illusory correlations, which appear to be links between variables that are not closely related at all.
4. Illusions

1. c. sensation.
2. a. transduction.
3. b. fatigue and motivation
4. d. cornea
5. b. rods and cones
6. a. afterimage effects; trichromatic
7. d. audition
8. c. neural impulses firing
9. b. 20%
10. a. thalamus
11. a. Feature detectors
12. a. proprioceptors
13. a. tension of the muscles focusing the eyes
14. d. proximity.
15. c. relative size.
16. Answers will vary. Examples might include judging distances to assess the safety of a situation; using vision to find food, water, or shelter; and seeing an attractive mate, which could be related to increasing reproductive success. Visual information in such cases increases the chances of survival.
17. The eye adjusts to drastic fluctuations in light levels, but this does not happen instantaneously, making it difficult to see when one first walks into a dark room. However, one’s eyes immediately begin to adjust. This process starts with the pupil, which rapidly shrinks and expands in response to light changes, and then continues with the rods and cones, which need more time to adjust to changes in lighting. After a few minutes, your eyes start to adjust to the dark in a process called dark adaptation, which takes about 8 minutes for cones and 30 minutes for rods. Cones respond more quickly, so they are more useful in the first few minutes of dark adaptation. The rods then begin to allow one to make out silhouettes of objects and people. To restore their sensitivity to light, rods and cones must undergo a chemical change associated with protein molecules, and this takes time.
18. Diagrams will vary; see Infographic 3.3. The pinna funnels sound waves into the auditory canal, focusing them toward the eardrum. Vibrations in the eardrum cause the hammer to push the anvil, which moves the stirrup, which presses on the oval window, amplifying waves. Pressure on the oval window causes fluid in the cochlea to vibrate and bend the hair cells on the basilar membrane. If vibration is strong enough in the cochlear fluid, the bending of hair cells causes nearby nerve cells to fire. The auditory nerve carries signals to the auditory cortex in the brain, where sounds are given meaning.
19. The gate-control theory of pain suggests that the perception of pain can either increase or decrease through the interaction of biopsychosocial factors. Signals are sent to open or close the “gates” that control the neurological pathways for pain. When large myelinated fibers are active, the gates are more likely to close, which then inhibits pain messages from being sent on. With a sore shoulder, applying ice to the injured area can stimulate the temperature and pressure receptors of the large fibers. This activity closes the gates, temporarily interfering with the pain message that would have been sent to the brain.
20. Answers will vary, but may include experiences such as getting into a hot tub and eventually becoming adapted to how hot it is; hearing the noise of a nearby highway at first, but then noticing it less as time passes.