Chichi: Sensation and perception

SENSATION & PERCEPTION I. SENSATION & PERCEPTION 1. Sensation - Sensation refers simply to your contact with the external world through your sensory receptors. These are the inputs received via our sensory receptors. 2. Perception - This refers to how we interpret and organize the information we receive from the senses. It is our conscious experience of what our senses are telling us. II. SENSATION 1. Stimulus - A stimulus is any form of energy to which our senses respond. For example, the light that hits our eyes would be considered a stimulus. 2. Sensory Receptors - In certain areas of our body we have specialized receptor cells that are programmed to respond to specific stimuli. They convert (or transduce) the physical properties of a stimuli into neural impulses that our brain can understand. 3. Sensory Deprivation - Our bodies are prepared to receive a great deal of sensory input. When we are deprived of sensory input our brains sometimes play a trick on us and tell us we are receiving information when we are not. This is usually in the form of hallucinations. 4. Absolute Threshold - Not all stimulation is received and translated. For example, a dog can hear sounds you cannot. The absolute threshold is the smallest amount of a stimulus that we can detect 50% of the time. 5. Signal Detection Theory - Some scientists dispute the existence of absolute thresholds. They propose a theory called signal detection theory. This holds that there are no absolute thresholds but rather, detection of a stimuli depends on the energy of the stimulus and the costs and benefits to you of detecting that stimulus. For example, if you are in a crowded room you do not hear what everyone is saying even though all sounds may meet a minimal threshold for hearing. You hear only those sound you deem important enough. 6. Difference Threshold - This is the amount two stimuli must differ for you to notice that they are different. This is illustrated by listening to your stereo. How much do you have to turn it up for you to notice that it is louder. Basically, the lower the intensity the easier it is to notice a difference. This is referred to a Weber's Law which states that the smallest detectable difference is a function of the intensity. 7. Subliminal Perception - There has been some interest in our ability to respond to stimuli that is below our threshold of conscious perception. This is very controversial and there is no agreement that it occurs. Some people believe however that there are satanic messages in rock albums. 8. Sensory Adaptation - Following prolonged stimulation, all sensory systems display adaptation which refers to an adjustment that decreases sensitivity. An example would be washing dishes. When you first put your hands under hot water the water seems very hot but gradually it does not seem that hot anymore. III. VISION 1. Structure of the Eye - The human eye has five main parts: cornea, pupil, iris, lens, and retina. The cornea is the transparent outer layer through which light passes. The pupil is the opening just behind the cornea through which light enters the eye. The iris is the colored part of the eye that adjusts the amount of light that enters the eye by constricting or dilating the pupil. The lens is just behind the pupil which bends the light to focus it on the retina which is at the back of the eye and converts the light into neural impulses that our brain can interpret. 2. Receptors on Retina - There are two types of receptors cells on the retina. Rods are responsible for responsible for light and dark reception and are more sensitive to movement. there are about 100 million rods on the retina. Cones are centered around the fovea and are responsible for color vision and feature detection. 3. Color Vision - There are two main theories that are used to explain color vision. Trichromatic Theory suggests that there are three types of cones each sensitive to different wavelengths. Some respond to red light, others green, and others blue. When each is stimulated you see that color, when more than one is stimulated you see the color between them. This has weaknesses. For example, it doesn't explain negative afterimages. This is when you stare at one color for a long time, when you look away you see the complementary color. Opponent-Process Theory states that there are three antagonistically organized systems. Two systems are composed of opposite colors (red-green & yellow-blue). When one is stimulated, the other is inhibited. When both are stimulated they cancel each other out. The other system responds to black and white. Experimental evidence suggests that color vision involves both systems. IV. HEARING 1. Outer Ear - This is the external, projecting portion of the ear. It consists of the pinna, the visible part and the auditory canal. 2. Middle Ear - This is separated from the outer ear by the eardrum and contains three small bones (hammer, anvil, & stirrup). 3. Inner Ear - Also called the cochlea which is a fluid filled chamber attached to the middle ear by a thin membrane called the oval window. 4. Perceiving Sound - Sound waves enter the ear, goes down the auditory canal and strikes the eardrum. The eardrum moves which causes vibration to the bones in the inner ear. They amplify the sound waves and apply pressure to the oval window which causes vibration of the fluid in the cochlea. There are hair cells in the cochlea which move with the fluid and convert the sound to neural signals which go to the brain. 5. Types of Sounds - Not all stimulation to the ear produces the same perception of sound. We perceive pitch, which is the highness or lowness of the sound. This is determined by the frequency of the sound wave. We also perceive the loudness of sound which is a function of the magnitude of the sound waves. Finally we perceive timbre which is the quality of the sound and is a function of the complexity of the sound wave. 6. Pitch Perception - There are two main theories on how we perceive different pitches. Place Theory suggests that sounds of different frequencies stimulate different areas of the cochlea. Frequency Theory suggests that sounds of different frequencies cause different rates of neural firing. In actuality, both theories explain pitch perception. Frequency theory explains low frequency sounds and place theory explains high frequency sounds. V. SKIN SENSES 1. Touch - There are sensory receptors in the skin that allow us to perceive touch. Sensitivity varies depending on the part of your body. Certain areas of the body have more receptors and a larger part of the brain devoted to them. Fingers and mouth are the most sensitive. 2. Warmth and Cold - Physiological zero is your skin temperature. If you touch something of this temperature you fell no temperature. There are warmth and cold receptors. Hot is perceived by simultaneous activation of warmth and cold receptors. 3. Pain - Pain has no specific receptors. Pain is caused by damage to bodily tissues which release chemical substances that stimulate pain neurons. VI. CHEMICAL SENSES 1. Smell and Taste - These are closely related senses. The principle function of smell is to warn you about potentially toxic substances. 2. Smell - To smell, molecules enter the nose and are dissolved in nasal tissue. This brings them into contact with receptor cells which sends the information to brain. Humans have about 10 million receptor cells. Dogs, however, have about 200 million. 3. Taste - There are four basic categories of taste: Sweet, sour, salty, and bitter. There are receptors for these on different parts of the tongue. the sensory receptors for taste are located in the taste buds. VII. BALANCE, POSTURE, AND MOVEMENT 1. Balance - This is called the vestibular sense. It is controlled by three semicircular canals within the cochlea in the inner ear. 2. Kinesthesis - This is your sense of body movement and position. It works with your vestibular and visual senses to maintain balance and equilibrium. The receptor cells for this sense are found in the nerve endings in and near joints, muscles, and tendons. VIII. PERCEPTION 1. Definition - Perception is an organism's awareness of objects and events in the environment brought about by stimulation of the sense organs. 2. Attention - We cannot be aware of all stimulation we receive at any time. You would be inundated with too much information. We selectively attend to certain aspects of our environment while relegating others to the background. 3. Perceptual Organization - This is the process by which the brain structures the input from our sensory receptors. 4. Gestalt Psychology - The Gestalt view of perception is that all humans organize or group information into meaningful patterns called gestalts. In other words, we view the whole rather than the parts. We tend to organize data by its proximity (how close together), continuity (is it a continuous grouping?), and similarity (the likeness of stimuli). We also view things in terms of figure and ground. This is our tendency to view something as the region that represents the object and its background. 5. Perceptual Constancy - This is our tendency to perceive objects as having certain constant, unchanging properties. Size Constancy is our tendency to perceive something as a certain size even though it is further away and makes a smaller image on the retina. Shape Constancy refers to our tendency to perceive a shape as the same even though the image on the retina may differ. the book gives the example of a coin. We see it as round even though we rarely see it this way. 6. Illusions - Sometimes our perceptions yield false interpretations of physical reality. Use transparencies to illustrate illusions. Moon Illusion: Why does the moon look bigger on horizon than when it is high in the sky? The image on the retina is the same. We know it if far away and when it is on the horizon we have visual cues such as trees and houses that trick us. We are still not quite sure if this is it however. 7. Depth Perception - This is usually derived from binocular disparity, the brain using the slight differences in information received from each eye to perceive depth. There are also cues that do not require the cooperation of both eyes. These are called monocular cues. Motion Parallax is the differences in the relative movement of retinal images that occur when we move or change position. Objects closer appear to move faster. Interposition is when one object partially blocks the view of another object creating the perception that the second object is farther away. Linear Perspective is the apparent convergence of two parallel lines in the distance. Relative Size is the relationship between the size of an image projected on the retina and the distance of the object from the observer. The larger the retinal image, the closer the object appears to be. Texture Gradient is the closer an object is to you, the more texture you can see. As an object gets farther away it appears smoother.