7 Sensation and Perception
STEP 4 Review the Knowledge You Need to Score High
Sensation—the process by which you detect physical energy from your environment and encode it as neural signals.
Psychophysics—the study of the relationship between physical energy and psychological experiences.
Stimulus—a change in the environment that can be detected by sensory receptors.
Absolute threshold—the weakest level of a stimulus that can be correctly detected at least half the time.
Signal detection theory—maintains that minimum threshold varies with fatigue, attention, expectations, motivation, emotional distress, and from one person to another.
Difference threshold—minimum difference between any two stimuli that a person can detect 50 percent of the time.
Just noticeable difference (jnd)—experience of the difference threshold.
Weber’s law—difference thresholds increase in proportion to the size of the stimulus.
Subliminal stimulation—receiving messages below one’s absolute threshold for conscious awareness.
Transduction—transformation of stimulus energy to the electrochemical energy of neural impulses.
Perception—the process of selecting, organizing, and interpreting sensations, enabling you to recognize meaningful objects and events.
Vision and the Human Eye
Rays of light from an object pass from the object through your cornea, aqueous humor, pupil, lens, and vitreous humor before forming an image on your retina.
Cornea—transparent, curved layer in the front of the eye that bends incoming light rays.
Iris—colored muscle surrounding the pupil that regulates the size of the pupil opening.
Pupil—small adjustable opening in the iris that is smaller in bright light and larger in darkness.
Lens—structure behind the pupil that changes shape, becoming more spherical or flatter to focus incoming rays into an image on the light-sensitive retina.
Accommodation—process of changing the curvature of the lens to focus light rays on the retina.
Retina—light-sensitive surface in the back of the eye containing rods and cones that transduce light energy. Also has layers of bipolar cells and ganglion cells that transmit visual information to the brain.
Fovea—small area of the retina in the most direct line of sight where cones are most concentrated for highest visual acuity in bright light.
Photoreceptors—modified neurons that convert light energy to electrochemical neural impulses. They include rods and cones:
• Rods—photoreceptors that detect black, white, and gray and that detect movement. Rods are necessary for peripheral and dim-light vision when cones do not respond. Distributed throughout the retina, except none are in the fovea.
• Cones—photoreceptors that detect color and fine detail in daylight or in bright-light conditions. Most concentrated at the fovea of the retina; none are in the periphery.
Bipolar cells—second layer of neurons in the retina that transmit impulses from rods and cones to ganglion cells.
Ganglion cells—third layer of neurons in the retina, whose axons converge to form the optic nerve.
Blind spot—region of the retina where the optic nerve leaves the eye so there are no receptor cells; creates an area with no vision.
Optic nerve—nerve formed by ganglion cell axons; carries the neural impulses from the eye to the thalamus of the brain.
Acuity—ability to detect fine details; sharpness of vision. Can be affected by small distortions in the shape of the eye.
Dark adaptation—increased visual sensitivity that gradually develops when it gets dark.
Feature detectors—individual neurons in the primary visual cortex/occipital lobes that respond to specific features of a visual stimulus.
Parallel processing—simultaneously analyzing different elements of sensory information, such as color, brightness, shape, etc.
Trichromatic theory—proposed mechanism for color vision with cones that are differentially sensitive to different wavelengths of light; each color you see results from a specific ratio of activation among the three types of receptors.
Opponent-process theory—proposed mechanism for color vision with opposing retinal processes for red—green, yellow—blue, white—black. Some retinal cells are stimulated by one of a pair and inhibited by the other.
Sensory adaptation—temporary decrease in sensitivity to a stimulus that occurs when stimulation is unchanging.
Attention—the set of processes from which you choose among the various stimuli bombarding your senses at any instant, allowing some to be further processed by your senses and brain.
Hearing and the Human Ear
Audition—the sense of hearing. The loudness of a sound is determined by the amplitude or height of the sound wave.
Frequency—the number of complete wavelengths that pass a point in a given amount of time. The wavelength is inversely proportional to the frequency. Frequency or wavelength determines the hue of a light wave and the pitch of a sound.
Pitch—the highness or lowness of a sound. The shorter the wavelength, the higher the frequency, the higher the pitch. The longer the wavelength, the lower the frequency, the lower the pitch.
Timbre—the quality of a sound determined by the purity of a waveform. What makes a note of the same pitch and loudness sound different on different musical instruments.
Sound localization—the process by which you determine the location of a sound.
Parts of the ear:
• The outer ear includes the pinna, the auditory canal, and the eardrum.
• The middle ear includes three tiny bones: the hammer, the anvil, and the stirrup.
• The inner ear includes the cochlea, semicircular canals, and vestibular sacs.
Cochlea—snail-shaped fluid-filled tube in the inner ear with hair cells on the basilar membrane that transduces mechanical energy of vibrating molecules to the electrochemical energy of neural impulses. Hair cell movement triggers impulses in adjacent nerve fibers.
Auditory nerve—axons of neurons in the cochlea converge transmitting sound messages through the medulla, the pons, and the thalamus to the auditory cortex of the temporal lobes.
Conduction deafness—loss of hearing that results when the eardrum is punctured or any of the ossicles lose their ability to vibrate. A hearing aid may restore hearing.
Nerve (sensorineural) deafness—loss of hearing that results from damage to the cochlea, hair cells, or auditory neurons. Cochlear implants may restore some hearing.
Place theory—the position on the basilar membrane at which waves reach their peak depends on the frequency of a tone. Accounts well for high-pitched sounds.
Frequency theory—the rate of the neural impulses traveling up the auditory nerve matches the frequency of a tone, enabling you to sense its pitch. Frequency theory explains well how you hear low-pitched sounds.
Somatosensation—the skin sensations: touch/pressure, warmth, cold, and pain.
Synesthesia—is a condition in which one sense (e.g., taste) is simultaneously perceived as if by one or more additional senses such as sight. Another form of synesthesia joins objects such as letters, shapes, numbers or people’s names with a sensory perception such as smell, color, or flavor.
Gate-control theory—pain is experienced only if the pain messages can pass through a gate in the spinal cord on their route to the brain. The gate is opened by small nerve fibers that carry pain signals and closed by neural activity of larger nerve fibers, which conduct most other sensory signals, or by information coming from the brain.
Kinesthesis—body sense that provides information about the position and movement of individual parts of your body with receptors in muscles, tendons, and joints.
Vestibular sense—body sense of equilibrium with hairlike receptors in semicircular canals and vestibular sac in the inner ear.
Gustation—the chemical sense of taste with receptor cells in taste buds in fungiform papillae on the tongue, on the roof of the mouth, and in the throat. Molecules must dissolve to be sensed. The five basic taste sensations are sweet, sour, salty, bitter, and, newly added to the list, umami or glutamate. Flavor is the interaction of sensations of taste and odor with contributions by temperature, etc.
Olfaction—the chemical sense of smell with receptors in a mucous membrane (olfactory epithelium) on the roof of the nasal cavity. Molecules must reach the membrane and dissolve to be sensed. Olfactory receptors synapse immediately with neurons of the olfactory bulbs in the brain with no pathways to the thalamus.
Attention—the set of processes by which you choose from among the various stimuli bombarding your senses at any instant, allowing some to be further processed by your senses and brain.
Selective attention—focused awareness of only a limited aspect of all you are capable of experiencing.
Bottom-up processing—information processing that begins with sensory receptors and works up to the brain’s integration of sensory information to construct perceptions; is data-driven.
Top-down processing—information processing guided by your preexisting knowledge or expectations to construct perceptions; is concept-driven.
Perceptual constancy—perceiving an object as unchanging even when the immediate sensation of the object changes.
Visual capture—vision usually dominates when there is a conflict among senses.
Gestalt psychologists recognized the importance of figure—ground in perception. They proposed organizing principles by which we perceive wholes rather than combinations of features including figure—ground, proximity, similarity, and continuity.
Depth perception—the ability to judge the distance of objects.
Monocular cues—clues about distance based on the image of one eye.
Monocular cues include interposition or overlap, relative size, aerial perspective or relative clarity, texture gradient, relative height or elevation, linear perspective, relative brightness, motion parallax, and accommodation.
Binocular cues—clues about distance requiring two eyes.
Binocular cues include the more important retinal disparity and less important convergence.
Optical or visual illusions—discrepancies between the appearance of a visual stimulus and its physical reality. Common examples of visual illusions include reversible figures, illusory contours, the Müller-Lyer illusion, the Ponzo illusion, and the moon illusion.
Schemas—concepts or frameworks that organize and interpret information.