The ABC’s of Sensation 3. 1 How do sensations travel through the central nervous system, and why are some sensations ignored? * Sensation is the activation of receptors located in the eyes, ears, skin, nasal cavities, and tongue. * Sensory receptors are specialized forms of neurons that are activated by different stimuli such as light and sound. * A just noticeable difference is the point at which a stimulus is detectable half the time it is present. * Weber’s law of just noticeable differences states that the just noticeable difference between two stimuli is always a constant. Absolute thresholds are the smallest amount of energy needed for conscious detection of a stimulus at least half the time it is present. * Subliminal stimuli are stimuli presented just below the level of conscious awareness and subliminal perception has been demonstrated in the laboratory. It has not been shown to be effective in advertising. * Habituation occurs when the brain ignores a constant stimulus. * Sensory adaption occurs when the sensory receptors stop responding to a constant stimulus. The Science of Seeing 3. 2 What is light, and how does it travel through the various parts of the eye? Brightness corresponds to the amplitude of light waves, whereas color corresponds to the length of the light waves. * Saturation is the psychological interception of wavelengths that are all the same (highly saturated) or varying (less saturated) * Light enters the eye and is focused through the cornea, passes through the aqueous humor, and then through the hole in the iris muscle called the pupil. * The lens also focuses the light on the retina, where it passes through ganglion and bipolar cells to stimulate the rods and cones. 3. How do the eyes see, and how do the eyes see different colors? * Rods detect changes in brightness but do not see color and function best in low levels of light. They do not respond to different colors and are found everywhere in the retina except the center, or fovea. * Cones are sensitive to colors and work best in bright light. They are responsible for the sharpness of visual information and are found in the fovea. * Trichromatic theory of color perception assumes four primary colors of red, green, blue, and yellow. All colors would be perceived as combinations of these three. Opponent-process theory of color perception assumes four primary colors of red, green, blue, and yellow. Colors arranged in pairs, and when one member of a pair is activated, the other is not. * Color blindness is a total lack of color precipitation whereas color-deficient vision refers to color perception that is limited primarily to yellows, and blues or reds and greens only. The Hearing Sense: Can You Hear Me Now? 3. 4 What is sound, and how does it travel through the various parts of the ear? * Sound has three aspects: pitch (frequency), loudness, and timbre (purity). Sound enters the ear through the visible outer structure, or pinna, and travels to the eardrum and then to the small bones of the middle of the ear. * The bone called the stirrup rests on the on the oval window, causing the cochlea and basilar membrane to vibrate with sound. * The organ of Corti on the basilar membrane contains the auditory receptors, which send signals to the brain about sound qualities as they vibrate. * Place theory states that the location of the hair cells on the organ of the Corti corresponds to different pitches of sound.
This can explain the pitch above 1000 Hz. * Frequency theory states that the speed with which the basilar membrane vibrates corresponds to different pitches of sound. This can explain pitch below 1000 Hz. * The volley principle states that neurons take turns firing for sounds above 400 Hz and below 4000 Hz. 3. 5 Why are some people unable to hear, and how can their hearing be improved? * Conduction hearing impairment is caused by damage to the outer or middle ear structures, whereas nerve hearing impairment is cause by damage to the inner ear or auditory pathways in the brain.
Chemical Senses: It Tastes Good and Smells Even Better 3. 6 How do the senses of taste and smell work, and how are they alike? * Gustation is the sense of taste. Taste buds in the tongue receive molecules of substances, which fit into receptor sites. * The five basic types of taste are sweet, sour, salty, bitter, and umami (brothy). * Olfaction is the sense of smell. The olfactory receptors in the upper part of the nasal passages receive molecules of substances and create neural signals that then go to the olfactory bulbs under the frontal lobes. Somesthetic Senses: What the Body Knows The somesthetic senses include the skin senses and the vestibular senses. 3. 7 What allows people to experience the sense of touch, pain, motion, and balance? * Pacinian corpuscles respond to pressure, certain nerve endings around hair follicles respond to pain and pressure, and free nerve endings respond to pain, pressure, and temperature. * The gate-control theory of pain states that when receptors sensitive to pain are stimulated, a neurotransmitter called substance P is released into the spinal cord, activating other pain receptors by opening “gates” in the spinal column and sending the message to the brain. The kinesthetic senses allow the brain to know the position and movement of the body through the activity of special receptors responsive to movement of the joints and limbs. * The vestibular sense also contributes to the body’s sense of spatial orientation and movement through the activity of the otolith organs (up-and-down movement) and the semicircular canals (movement through areas). * Motion sickness is explained by sensory conflict theory, in which information from the eyes conflicts with information from the vestibular sense, causing nausea.
The ABC’s of Perception 3. 8 What are perception and perceptual constancies? * Perception is the interception and organization of sensations. * Size constancy is the tendency to perceive objects as always being the same size, no matter how close or far away they are. * Shape constancy is the tendency to perceive objects as remaining the same shape even when the shape of the object changes on the retina of the eye. * Brightness constancy is the tendency to perceive objects as a certain level of brightness, even when the light changes. 3. What are the Gestalt principles of perception? * The Gestalt psychologists developed several principles perception that involves interpreting patterns in visual stimuli. The principles are figure-ground relationships, closure, similarity, continuity, contiguity, and common region. 3. 10 What is depth perception, and what kinds of cues are important for it to occur? * Depth perception is the ability to see in three dimensions. * Monocular cues for depth perception include linear perspective, relative size, overlap, aerial (atmospheric) perspective, exture gradient, motion parallax, and accommodation * Binocular cues for depth perception include convergence and binocular overlap 3. 11 What are visual illusions and how can they and other factors influence and alter perception? * Illusions are perceptions that do not correspond to reality or are distortions of visual stimuli. * Perceptual set or expectancy refers to the tendency to perceive objects and stimulations in a particular way because of prior experiences. * Top-down processing involves the use of preexisting knowledge to organize individual features into a unified whole. Bottom-up processing involves the analysis of smaller features, building up to a complete perception. Applying Psychology to Everyday Life: Beyond “Smoke and Mirrors”- The Psychological Science and Neuroscience of Magic * Magicians take advantage of some well-known properties or our visual system, to accomplish a variety of magic tricks. * By collaborating with magicians, psychologists and neuroscientists can learn more about magic and the brain processes responsible for our perception of magic tricks.