I. IntroductionA. Sensation -- the process by which our sensory receptors respond to light, sound, color, textures, and taste and transmit that information to the brain■ Our eyes, ears, nose, tongue, and skin receive and process information from the environment.■ Each sense organ contain receptor cells that transmit neural impulses to the brain.■ When adults are totally deprived of sensory input, they experience hallucinations.B. Perception -- the process by which the brain actively selects, organizes, and assigns meaning to incoming messages.II. Basic Principles of SensationA. Transduction -- the process by which sensory receptors convert the incoming physical energy of stimuli into neural impulses that the brain can understand■ This process is so quick it seems immediate but occurs only when the neural impulses reach the brain.B. Thresholds■ Absolute Threshold -- the minimum amount of a stimulus that an observer can reliably detect■ Difference Threshold -- the minimal difference needed to notice a stimulus change, it is also called the “just noticeable difference”■ Weber’s Law -- German psychologist Ernst Weber observed that the just noticeable difference will vary depending on its relation to the original stimulus. The size of the just noticeable difference is proportional to the strength of the original stimulus.● For example, a bencher pressing 50 lb would notice 5 lb increase, but one benching 500 lb would not notice the extra 5 lb.C. Signal Detection Theory■ This theory assumes that there is no single absolute threshold. Instead, a detection depends upon a combination of stimulus intensity, background noise, and a person’s physical conditionD. Sensory Adaptation■ This occurs when a constant stimulus is presented for a length of time. When this happens receptors fire less frequently and the sensation often fades or disappears.III. The Human Visual SystemA. Introduction -- The visual system is our most complex and important sense.B. From the Cornea to the Retina■ Cornea -- is a clear membrane covering the visible part of the eye. It protects the eye and helps gather and direct incoming light waves.■ Pupil -- the small opening in the middle of the iris■ Iris -- the colored part of the eye■ Lens -- a transparent structure located behind the pupil that actually focuses and bends light as it enters the eyeC. The All-Important Retina■ The retina is the light-sensitive membrane at the back of the eye. It contains millions of sensory receptors for vision.■ Rods -- photoreceptors in the retina that are especially sensitive to dim light■ Cones -- photoreceptors in the retina that are especially sensitive to color and bright lights■ Blind spot -- the point where the optic nerve leaves the eye and where there are no rods or cones. We are normally unaware of it because our eyes are always moving.D. The Visual Cortex■ The optic nerve carries visual information to the brain’s visual cortex, which is at the back of the brain.E. Color Vision■ Two ways that color vision works:● Trichromatic -- begins with the fact that there are three primary colors and any color can be made by combining these three.● Opponent- Process Theory -- believes cells process color in opposing pairs of red or green, black or white, and blue or yellow colors. This is the reasons we get after images.■ Color Blindness -- cone deficiency that prevents a person from distinguishing between certain colors.IV. The Human Auditory SystemA. Introduction■ Hearing plays a vital role in language development and social interactions. It also alerts us to dangerous situations.■ It turns sound waves into neural messages that the brain processesB. The Outer Ear■ Collects sound waves, sound travels down the auditory canal and bounces into the eardrum, a tightly stretched membrane located at the end of the auditory canal.C. The Middle Ear■ Hammer, Anvil, and Stirrup -- three tiny bones in the middle ear amplifies the soundD. The Inner Ear■ The inner ear transfers sound waves into neural messages.■ Cochlea -- a spiral-shaped, fluid-filled structure that contains the basilar membrane and hair cells■ Basilar membrane -- runs the length of the cochlea and holds the hair cell receptors for hearing■ Hair cells -- they transfer the physical vibration of the sound waves into neural impulsesE. The Brain■ As the hair cells bend, they stimulate the cells of the auditory nerve and the auditory nerve carries the neural messages to the brainF. Distinguishing Pitch■ Pitch -- is the relative highness or lowness of a sound■ Frequency Theory -- explains how low-frequency sounds are transmitted to the brain■ Place Theory -- different frequencies excite different hair cells at different locations along the basilar membraneG. The Loss of Hearing■ Conduction deafness● Caused when the tiny bones in the middle ear are damaged and can’t transmit sound waves to the inner ear● Hearing aids can amplify sound and help overcome conduction deafness■ Nerve deafness -- caused by damage to the cochlea, hair cells, or auditory nerve. Playing headphones loudly can cause permanent hearing loss. Hearing aids can’t help nerve deafness as damage is irreversible.V. The Chemical SensesA. Smell and taste are the chemical senses. Their receptors are near each other, so it is often difficult to separate the two.B. Olfaction (Smell)■ Receptor cells communicate neural messages to the olfactory center. Smell is capable of triggering vivid memories and emotions. Six qualities: fragrant, burnt, putrid, spicy, resinous, and etheral.C. Gustation (Taste)■ Our tongue is covered with papillae, which are in turn covered with taste buds. Humans have a four major taste sensations: bitter, sweet, sour, and saltyVI. Skin and Body SensesA. Skin■ Our largest and heaviest sense organ. It protects our internal organs, holds body fluids, produces sensations of touch, warmth, and cold and provides information about pain.■ Body sense provides information about your position in spaceB. Skin Senses:■ Touch -- receptors are not evenly distributed. Touch plays an important role in human relationships■ Pain -- is physical discomfort to warm of injury.C. The Vestibular Sense■ Vestibular sense provides a sense of balance and equilibrium■ The inner ear is important for maintaining balance■ The semicircular canals provide the brain with important information about the body’s posture and head