Sostenibilidad y permanencia

15. The environmental stimuli for smell, or olfaction, are invisible

molecules of gas emitted by substances and suspended in the air. As air enters the nose, it flows into the olfactory epithelium, where hundreds of different types of receptors respond to vari- ous kinds of molecules, producing complex smells. The axons of olfactory receptor cells constitute the olfactory nerve, which transmits information to the olfactory bulbs under the frontal lobes and on to the primary olfactory cortex, a primitive region of the cortex deep in the frontal lobes.

16. Taste, or gustation, is sensitive to molecules soluble in saliva.

Much of the experience of flavor, however, is really contributed by smell. Taste occurs as receptors in the taste buds on the tongue and throughout the mouth transduce chemical informa- tion into neural information, which is integrated with olfactory information in the brain.

17. Touch actually includes three senses: pressure, temperature, and pain. The human body contains approximately 5 million touch receptors of at least seven different types. Sensory neurons synapse with spinal interneurons that stimulate motor neurons, allowing reflexive action. They also synapse with neurons that carry information up the spinal cord to the medulla, where nerve tracts cross over. From there, sensory information travels to the thalamus and is subsequently routed to the primary touch center in the brain, the somatosensory cortex, which contains a map of the body.

18. Pain is greatly affected by beliefs, expectations, and emotional

state.

19. The proprioceptive senses provide information about the body’s

position and movement. The vestibular sense provides infor- mation on the position of the body in space by sensing gravity and movement. Kinesthesia provides information about the movement and position of the limbs and other parts of the body relative to one another.

PERCEPTION

20. The hallmarks of perception are organization and interpretation. Perceptual organization integrates sensations into meaningful

units, locates them in space, tracks their movement, and pre- serves their meaning as the perceiver observes them from differ- ent vantage points. Form perception refers to the organization of sensations into meaningful shapes and patterns (percepts). The Gestalt psychologists described several principles of form perception, including figure–ground perception, similarity,

proximity, good continuation, simplicity, and closure. A more

recent theory, called recognition-by-components, asserts that we perceive and categorize objects in the environment by break- ing them down into component parts, much like letters in words.

21. Depth perception is the organization of perception in three

dimensions. Depth perception organizes two-dimensional retinal images into a three-dimensional world, primarily through

binocular and monocular visual cues.

22. Motion perception refers to the perception of movement. Two

systems appear to be involved in motion perception. The first computes motion from the changing image projected by the ob- ject on the retina; the second makes use of commands from the brain to the muscles in the eye that signal eye movements.

23. Perceptual constancy refers to the organization of changing sen-

sations into percepts that are relatively stable in size, shape, and color. Three types of perceptual constancy are size, shape, and

color constancy, which refer to the perception of unchanging

size, shape, and color despite momentary changes in the retinal image. The processes that organize perception leave perceivers vulnerable to perceptual illusions, some of which appear to be innate and others of which depend on culture and experience.

24. Perceptual interpretation involves generating meaning from sen-

sory experience. Perceptual interpretation lies at the intersection of sensation and memory, as the brain interprets current sensa- tions in light of past experience. Perception is neither entirely in- nate nor entirely learned. The nervous system has certain innate potentials, but these potentials require environmental input to develop. Experience can alter the structure of the brain, making it more or less responsive to subsequent sensory input. Accord- ing to the theory of direct perception, the meaning or adaptive significance of a percept is obvious, immediate, and innate.

25. Bottom-up processing refers to processing that begins “at the

bottom,” with raw sensory data that feeds “up” to the brain.

Top-down processing starts “at the top,” from the observer’s

expectations and knowledge. According to current thinking, perception proceeds in both directions simultaneously.

26. Experience with the environment shapes perceptual interpreta-

tion by creating perceptual expectations called perceptual set. Two aspects of perceptual set are current context and enduring knowledge structures called schemas. Motives, like expectations, can influence perceptual interpretation.

kEY TERMS 161

K E y T E R M S

absolute threshold 111 accommodation 118 amplitude 130 audition 129 auditory nerve 133 binocular cells 146 binocular cues 146 bipolar cells 118 blindsight 123 blind spot 118 bottom-up processing 155 closure 143 cochlea 132 color constancy 149 complexity 130 cones 118 cornea 117 cycle 129 decibels (dB) 130

depth or distance perception 145 difference threshold 112 direct perception 152 eardrum or tympanic membrane 131 feature detectors 123 Fechner’s law 114 figure–ground perception 143 form perception 142 fovea 118 frequency 129 frequency theory 133 ganglion cells 118 good continuation 143 gustation 136 hair cells 132 hertz (Hz) 129 hue 126 iris 117

just noticeable difference (jnd) 112 kinesthesia 141 lens 118 lightness 126 loudness 130 monocular cues 146 motion detectors 148 motion parallax 147 motion perception 148 Müller–Lyer illusion 151 olfaction 135 olfactory epithelium 135 olfactory nerve 135 opponent-process theory 128 optic nerve 118 perception 108 percepts 142 perceptual constancy 149 perceptual illusions 145 perceptual interpretation 152 perceptual organization 142 phantom limbs 138 pheromones 135 pitch 129 place theory 133 proprioceptive senses 141 proximity 143 psychophysics 109 pupil 117 receptive field 120 recognition-by-components 144 retina 118 rods 118 saturation 126 schemas 157 sensation 108 sensory adaptation 114 sensory receptors 111 shape constancy 150 similarity 143 simplicity 143 size constancy 150 sound localization 134 sound waves 129 Stevens’s power law 114 taste buds 136 timbre 130 top-down processing 155 transduction 111 vestibular sense 141 visual cliff 154 wavelength 116 Weber’s law 112 “what”pathway 124 “where” pathway 124 Young–Helmholtz

(or trichromatic) theory of color 127

n experiment by John Garcia and his colleagues adds a new twist to all the stories ever told about wolves and sheep. The researchers fed a wolf a muttonburger (made of the finest sheep flesh) laced with odorless, tasteless capsules

of lithium chloride, a chemical that induces nausea. Displaying a natural preference for mutton, the animal wolfed it down but half an hour later became sick and vomited (Garcia & Garcia y Robertson, 1985; Gustavson et al., 1976).

Several days later, the researchers introduced a sheep into the wolf’s compound. At the sight of one of its favorite delicacies, the wolf went straight for the sheep’s throat. But on contact, the wolf abruptly drew back. It slowly circled the sheep. Soon it attacked from another angle, going for the hamstring. This attack was as short lived as the first. After an hour in the compound together, the wolf still had not attacked the sheep—in fact, the sheep had made a few short charges at the wolf! Lithium chloride seems to have been the real wolf in sheep’s clothing.

Although the effects of a single dose of a toxic chemical do not last forever, Gar- cia’s research illustrates the powerful impact of learning. In humans, as in other animals,

learning is central to adaptation. Knowing how to distinguish edible from inedible foods, or friends from enemies or predators, is essential for survival. The range of possible foods or threats is simply too great to be prewired into the brain. Learning is essentially about predicting the future from past experience and using these predictions to guide behavior. For example, even the simplest organisms respond to the environment with reflexes. A

reflex is a behavior that is elicited automatically by an environmental stimulus, such as

the knee-jerk reflex elicited by a doctor’s rubber hammer. (A stimulus is something in the

environment that elicits a response.) In perhaps the simplest form of learning, habituation, organisms essentially learn what they can ignore. Habituation refers to the decreasing

strength of a response after repeated presentations of the stimulus.

Theories of learning generally share three assumptions. The first is that experience shapes behavior. Particularly in complex organisms such as humans, the vast majority of responses are learned rather than innate. The migration patterns of Pacific salmon may be instinctive, but the migration of college students to Daytona Beach during spring break is not. The second is that learning is adaptive. Just as nature eliminates organisms that are not well suited to their environments, the environment naturally selects those behaviors in an individual that are adaptive and weeds out those that are not (Skinner, 1977). Behav- iors useful to the organism (such as avoiding fights with larger members of its species) will be reproduced because of their consequences (safety from bodily harm). A third assump- tion is that careful experimentation can uncover laws of learning, many of which apply to human and nonhuman animals alike.

Learning theory is the foundation of the behaviorist perspective, and the bulk of this chapter explores the behavioral concepts of classical and operant conditioning (known together as associative learning). The remainder examines cognitive approaches that

learning any relatively permanent change in

the way an organism responds based on its experience

reflexes behaviors elicited automatically by

environmental stimuli

stimulus an object or event in the

environment that elicits a response in an organism

habituation the decreasing strength of a

response after repeated presentation of the stimulus

A

163

emphasize the role of thought and social experience in learning. What unites these two approaches is a common philosophical ancestor: the concept of association. Twenty-five hundred years ago, Aristotle proposed a set of laws of association to account for learn-

ing and memory. The most important is the law of contiguity, which proposes that two events will become connected in the mind if they are experienced close together in time (such as thunder and lightning). Another is the law of similarity, which states that objects that resemble each other (such as two people with similar faces) are likely to become associated.

As we saw in Chapter 1, a fundamental aspect of the behaviorist agenda was to rid psychology of terms such as thoughts and motives. The aim was to create a science of

behavior that focuses on what we can directly observe. As we will see, decades of behav-

ioral research have produced extraordinary progress in our understanding of learning, as well as substantial challenges to some of the assumptions that generated that research.

I N t e r I M S U M M a r Y

Learning refers to any enduring change in the way an organism responds based on its

experience. Learning theories assume that experience shapes behavior, that learning is adaptive, and that only systematic experimentation can uncover laws of learning. Principles of association are fundamental to most accounts of learning.

C L A S S I C A L C O N D I T I O N I N G

Classical conditioning (sometimes called Pavlovian or respondent conditioning)

was the first type of learning to be studied systematically. In the late nineteenth century, the Russian physiologist Ivan Pavlov (1849–1936) was studying the diges- tive systems of dogs. During the course of his work, he noticed a peculiar phenom- enon. Like humans and other animals, dogs normally salivate when presented with food, which is a simple reflex. Pavlov noticed that if a stimulus, such as the ringing of a bell or a tuning fork, repeatedly occurred just as a dog was about to be fed, the dog would start to salivate when it heard the bell even if the food was not present. As Pavlov understood it, the dog had learned to associate the bell with food, and because food produced the reflex of salivation, the bell also came to produce the reflex.

In document Director Ingeniería de Sistemas Luis Antonio García. Director Ingeniería Industrial Arturo Rojas Rincón. Director Ingeniería Electrónica (página 58-62)