CHAPTER 3 SENSATION AND PERCEPTION

 

Sensation - The process by which our sense receptors and nervous system receive and represent stimulus energies from our environment.

Perception - The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.

Absolute Threshold - The minimum stimulation needed to detect a particular stimulus.

Difference Threshold - The minimum difference in stimulation that a subject can detect 50% of the time. We experience the difference threshold as a just noticeable difference (jnd).

Electromagnetic Radiation

Electromagnetic Spectrum (Wavelength)

Visible Light

Major Eye Structures (Show Overhead S&P 2)

The Young-Helmholtz Trichromatic Theory

The Opponent Process Theory

Signal Detection Theory

Color Vision

Lateral Inhibition

Depth Perception - The ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance.

Binocular Cues - Depth cues, such as retinal disparity and convergence, that depend on the use of two eyes.

Monocular Cues - Distance cues, such as aerial and linear perspective and overlap, available to either eye alone.

Visual Illusions

Ambiguous Images

Impossible Images

Gestalt Principles

Visual Capture -- The tendency for vision to dominate the other senses; we perceive filmed voices as coming from the screen we see rather than from the projector behind us.

Hearing

Sound Attributes

Ear Structures

Responding to Sound

Chemical Senses

Olfaction (Smell)

Taste

Taste Buds

Taste Changes

Skin Senses

Pain

Endorphins

Body Senses

Subliminal Persuasion

Extra-Sensory Perception

Okay, now here's a kinda put all together sort of thing ...

SENSATION To study sensation is to study an ageless question: How does the world "out there" get represented inside our heads? Put another way, how are the external stimuli that strike our bodies transformed into messages that our brains comprehend? Some Basic Principles Each species comes equipped with sensitivities that enable it to survive and thrive. We sense only a portion of the sea of energy that surrounds us, but to this portion we are exquisitely sensitive. Our absolute threshold for any stimulus is the minimum stimulation necessary for us to detect it. Signal detection researchers report that our individual absolute thresholds vary with our psychological state. Can we react to stimuli that are not only subthreshold (subliminal), but so weak that we could never consciously perceive them? Recent experiments reveal that we can process some information from stimuli too weak to recognize. But the restricted conditions under which this occurs would not enable unscrupulous opportunists to exploit us with subliminal messages. Nor is there any evidence or plausible theory that we can effortlessly "reprogram" our minds with subliminal tapes. To survive and thrive, an organism must also have difference thresholds low enough to detect minute changes in important stimuli. In humans, difference thresholds (also called just noticeable differences, or jnd's) increase in proportion to the size of the stimulus - a principle known as Weber's Law. The phenomenon of sensory adaption focuses our attention on changing stimulation by diminishing our sensitivity to constant or routine odors, sounds, and touches. Vision The task of our visual sense, as of each of our senses, is to receive stimulation, transduce it into neural signals, and send these neural messages to the brain. The energies we experience as visible light are a thin slice from the broad spectrum of electromagnetic radiation. After entering the eye through a cameralike lens, light waves strike the retina. the retina's rods and cones convert the light energy into neural impulses, which are coded by the retina before traveling up the optic nerve to the brain. Visual Information Processing In the cortex, individual neurons respond to specific features of a physical stimulus, and their information is pooled by higher-level brain cells for interpretation. Subdimensions of vision (color, movement, depth, and form) are processed separately and simultaneously, illustrating our brain's capacity for parallel processing. Color Vision Research on how we see color supports two nineteenth-century theorists. First, as the Young-Helmholtz three-color theory suggests, the retina contains three types of cones. Each is most sensitive to the wavelengths of the three primary colors (red, green, and blue). Second, as opponent-process theory maintains, the nervous system codes the color-related information from the cones into pairs of opponent colors, as demonstrated by the phenomenon of after-images and as confirmed by measuring opponent processes within the visual neurons of the thalamus. As illustrated by the phenomenon of color constancy under varying illumination, our brains construct our experience of color. Hearing The pressure waves we experience as sound vary in frequency and amplitude, and correspondingly in perceived pitch and loudness. Through a mechanical chain of events, sound waves traveling through the auditory canal cause minuscule vibrations in the eardrum. Transmitted via the bones of the middle ear to the fluid-filled cochlea, these vibrations create movement in tiny hair cells, triggering neural messages to the brain.
Research on how we hear pitch supports both the place theory, which best explains the sensation of high-pitched sounds, and frequency theory, which best explains the sensation of low-pitched sounds. We localize sound by detecting minute differences in the loudness and timing of the sounds received by each ear. Hearing Loss Hearing loss linked to conduction and nerve disorders can be caused by prolonged exposure to loud noise and by diseases and age-related disorders. Touch Our sense of touch is actually four senses: pressure, warmth, cold, and pain, that combine to produce other sensations, such as "hot." One theory of pain is that a "gate" in the spinal cord either opens to permit pain signals traveling up small nerve fibers to reach the brain or closes to prevent their passage. Because pain is both a psychological and physiological phenomenon, it often can be controlled through a combination of medical and psychological treatments. Taste Taste, a chemical sense, is likewise a composite of four basic sensations: sweet, salty, sour, and bitter, and of the aromas that interact with information from the taste buds. Smell Like taste, smell is a chemical sense, but there are no basic sensations for smell, as there are for touch and taste. Like other stimuli, odors can spontaneously evoke memories and feelings. Body Position & Movement (Kinethetics) Our effective functioning requires a kinesthetic sense, which notifies the brain of the position and movement of body parts, and a sense of equilibrium, which monitors the position and movement of the whole body. Sensory Restriction People temporarily or permanently deprived of one of their senses typically compensate by becoming more acutely aware of information from the other senses. Temporary experiences of sensory restriction often evoke a heightened awareness of all forms of sensation. Under supervision, sensory restriction may provoke a therapeutic boost for those seeking control over problems such as smoking. PERCEPTION From a top-down perspective, we see how, aided by knowledge and expectations, we transform sensory information into meaningful perceptions. Perceptual Illusions Visual and auditory illusions were fascinating scientists even as psychology emerged. Explaining illusions required an understanding of how we transform sensations into meaningful perceptions, so the study of perception became one of psychology's first concerns. Conflict between visual and other information is usually resolved with the mind accepting the visual data, a tendency known as visual capture. Perceptual Organization The early Gestalt psychologists were impressed with the seemingly innate way in which we organize fragmentary sensory data into whole perceptions. Our minds structure the information that comes to us in several demonstrable ways: Form Perception -- To reorganize an object, we must firrst perceive it (see it as a figure) as distinct from surrounding stimuli (the ground). We must also organize the figure into a meaningful form. Several Gestalt principles - proximity, continuity, closure, and connectedness - describe this process. Depth Perception -- Research on the visual cliff reveals that many species perceive the world in three dimensions at, or very soon after, birth. We transform two-dimensional retinal images into three-dimensional perception by using binocular cues, such as retinal disparity, and monocular cues, such as the relative sizes of objects. Perceptual Constancy - Having perceived an object as a coherent figure and located it in space, how do we recognize it - despite the varying images that may cast upon our retinas? Size, shape, and brightness constancies describe how objects appear to have unchanging characteristics regardless of their distance, shape, or motion. These constancies explain several of the well-known illusions. For example, familiarity with the size-distance relationships in a carpentered world of rectangular shapes makes people more susceptible to the Muller-Lyer illusion. Sensory Restriction and Restored Vision For many species, infancy is a critical period during which experience must activate the brain's innate visual mechanisms. If cataract removal restores eyesight to adults who were blind from birth, they remain unable to perceive the world normally. Generally, they can distinguish figure from ground and perceive colors, but they are unable to distinguish shapes and forms. In controlled experiments, infant kittens and monkeys have been reared with severely restricted visual input. When their visual exposure is returned to normal, they, too, suffer enduring visual handicaps. Perceptual Adaption Human vision is remarkably adaptable. Given glasses that shift the world slightly to the left or right, or even turn it upside down, people manage to adapt their movements and, with practice, to move about with ease. Perceptual Set Clear evidence that perception is influenced by our experience - our learned assumptions and beliefs - as well as by sensory input comes from the many demonstrations of perceptual set and context effects. The schemas we have learned help us to interpret otherwise ambiguous stimuli, a fact that helps explain why some of us "see" monsters, faces, and UFOs that others do not. Is There Perception Without Sensation? Many people believe in or claim to experience extrasensory perception. Parapsychologists have tried to document several forms of ESP - telepathy, clairvoyance, and precognition. But for several reasons, especially the lack of reproducible ESP effect, most research psychologists remain skeptical.