Chapter 5 Psych: Sensation and Perception

Smell (Olfaction)

Olfactory receptor cells are located in a mucous membrane at the top of the nose. Small hair-like extensions from these receptors serve as the sites for odor molecules dissolved in the mucus to interact with chemical receptors located on these extensions (Figure 5.20). Once an odor molecule has bound a given receptor, chemical changes within the cell result in signals being sent to the olfactory bulb: a bulblike structure at the tip of the frontal lobe where the olfactory nerves begin. From the olfactory bulb, information is sent to regions of the limbic system and to the primary olfactory cortex, which is located very near the gustatory cortex.

Transduction

The conversion from sensory stimulus energy to action potential is known as

Sensation

When sensory information is detected by a sensory receptor, sensation has occurred. For example, light that enters the eye causes chemical changes in cells that line the back of the eye.

5.2 Waves and Wavelengths

Frequency refers to the number of waves that pass a given point in a given time period and is often expressed in terms of hertz(Hz),or cycles per second. Longer wavelengths will have lower frequencies, and shorter wavelengths will have higher frequencies. The frequency of a sound wave is associated with our perception of that sound's pitch. Loudness is measured in terms of decibels (dB), a logarithmic unit of sound intensity.

5.4 Hearing

Our auditory system converts pressure waves into meaningful sounds.

Perception,

Perception refers to the way sensory information is organized,interpreted, and consciously experienced. Perception involves both bottom-up and top-down processing. Bottom-up processing refers to the fact that perceptions are built from sensory input. On the other hand, how we interpret those sensations is influenced by our available knowledge, our experiences, and our thoughts. This is called top-down processing. One way to think of this concept is that sensation is a physical process, whereas perception is psychological. Although our perceptions are built from sensations, not all sensations result in perception. In fact, we often don't perceive stimuli that remain relatively constant over prolonged periods of time. This is known as sensory adaptation. Failure to notice something that is completely visible because of a lack of attention is called inattentional blindness. The ability to identify a stimulus when it is embedded in a distracting background is called signal detection theory. This might also explain why a mother is awakened by a quiet murmur from her baby but not by other sounds that occur while she is asleep.

General layout of ears

The outer ear includes the pinna, which is the visible part of the ear that protrudes from our heads, the auditory canal, and the tympanic membrane, or eardrum. The middle ear contains three tiny bones known as the ossicles, which are named the malleus (or hammer), incus (or anvil), and the stapes (or stirrup). The inner ear contains the semi-circular canals, which are involved in balance and movement (the vestibular sense) , and the cochlea. The cochlea is a fluid filled, snail-shaped structure that contains the sensory receptor cells (hair cells) of the auditory system.

TOUCH, THERMOCEPTION, AND NOCICEPTION

These nerve endings respond to a variety of different types of touch-related stimuli and serve as sensory receptors for both thermoception (temperature perception) and nociception (a signal indicating potential harm and maybe pain. Generally speaking, pain can be considered to be neuropathic or inflammatory in nature. Pain that signals some type of tissue damage is known as inflammatory pain. In some situations, pain results from damage to neurons of either the peripheral or central nervous system. As a result, pain signals that are sent to the brain get exaggerated. This type of pain is known as neuropathic pain.

Hearing Loss

Deafness is the partial or complete inability to hear. Some people are born deaf, which is known as congenital deafness. Many others begin to suffer from conductive hearing loss because of age, genetic predisposition,or environmental effects, including exposure to extreme noise, certain illnesses (such as measles or mumps), or damage due to toxins (such as those found in certain solvents and metals).

How Auditory System Works

Sound waves travel along the auditory canal and strike the tympanic membrane, causing it to vibrate.This vibration results in movement of the three ossicles. As the ossicles move, the stapes presses into a thin membrane of the cochlea known as the oval window. As the stapes presses in to the oval window, the fluid inside the cochlea begins to move, which in turn stimulates hair cells,which are auditory receptor cells of the inner ear embedded in the basilar membrane. The basilar membrane is a thin strip of tissue within the cochlea. The temporal theory of pitch perception asserts that frequency is coded by the activity level of a sensory neuron. The place theory of pitch perception suggests that different portions of the basilar membrane are sensitive to sounds of different frequencies.

5.3 Vision

The cornea is the transparent covering over the eye. It serves as a barrier between the inner eye and the outside world, and it is involved in focusing light waves that enter the eye. The pupil is the small opening in the eye through which light passes, and the size of the pupil can change as a function of light levels as well as emotional arousal. The pupil's size is controlled by muscles that are connected to the iris, which is the colored portion of the eye. After passing through the pupil, light crosses the lens, a curved, transparent structure that serves to provide additional focus. The lens is attached to muscles that can change its shape to aid in focusing light that is reflected from near or far objects. In a normal-sighted individual, the lens will focus images perfectly on a small indentation in the back of the eye known as the fovea, which is part of the retina, the light sensitive lining of the eye. The fovea contains densely packed specialized photoreceptor cells.These photoreceptor cells, known as cones, are light-detecting cells. The cones are specialized types of photoreceptors that work best in bright light conditions. Cones are very sensitive to acute detail and provide tremendous spatial resolution. They also are directly involved in our ability to perceive color. While cones are concentrated in the fovea, where images tend to be focused, rods, another type of photoreceptor, are located throughout the remainder of the retina. Rods are specialized photoreceptors that work well in low light conditions, and while they lack the spatial resolution and color function of the cones, they are involved in our vision in dimly lit environments as well as in our perception of movement on the periphery of our visual field. Axons from the retinal ganglioncellsconvergeandexitthroughthebackoftheeyetoformtheopticnerve.The optic nerve carries visual information from the retina to the brain. There is a point in the visual field called the blind spot. The optic nerve from each eye merges just below the brain at a point called the optic chiasm.

Absolute Threshold

The sensitivity of a given sensory system to the relevant stimuli can be expressed as an absolute threshold. Absolute threshold refers to the minimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the time. It is also possible for us to get messages that are presented below the threshold for conscious awareness—these are called subliminal messages. It is also possible for us to get messages that are presented below the threshold for conscious awareness—these are called subliminal message Sometimes, we are more interested in how much difference in stimuli is required to detect a difference between them. This is known as the just noticeable difference (jnd) or difference threshold. Unlike the absolute threshold, the difference threshold changes depending on the stimulus intensity.

THE VESTIBULAR SENSE, PROPRIOCEPTION, AND KINESTHESIA

The vestibular sense contributes to our ability to maintain balance and body posture. Therefore, both proprioception (perception of body position) and kinesthesia (perception of the body's movement through space) interact with information provided by the vestibular system. One Gestalt principle is the figure-ground relationship. According to this principle, we tend to segment our visual world into figure and ground. Figure is the object or person that is the focus of the visual field, while the ground is the background. Another Gestalt principle for organizing sensory stimuli into meaningful perception is proximity. We might also use the principle of similarity to group things in our visual fields. Two additional Gestalt principles are the law of continuity (or good continuation) and closure. The law of continuity suggests that we are more likely to perceive continuous, smooth flowing lines rather than jagged, broken lines. The principle of closure states that we organize our perceptions into complete objects rather than as a series of parts.

Taste (Gustation)

You have learned since elementary school that there are four basic groupings of taste: sweet, salty, sour, and bitter. Research demonstrates, however, that we have at least six taste groupings. Umami is our fifth taste. Umami is actually a Japanese word that roughly translates to yummy, and it is associated with a taste for monosodium glutamate (Kinnamon & Vandenbeuch, 2009). There is also a growing body of experimental evidence suggesting that we possess a taste for the fatty content of a given food. Taste buds are formed by groupings of taste receptor cells with hair-like extensions that protrude into the central pore of the taste bud