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Unformatted text preview: Chapter 3 Summary Sensation allows us to receive information from the world around us. Synesthesia is the rare condition in which a person experiences more than one sensation from a single stimulus, for example the person who can hear and see a sound. Outside stimuli (such as the sound of your mothers voice) activate sensory receptors which convert the outside stimulus into a message that our nervous system can understand electrical and chemical signals. The process of converting the outside stimulus into the electrical-chemical signal of the nervous system is called sensory transduction . The sensory receptors are specialized forms of neurons and make up part of our somatic nervous system. Ernst Weber and Gustav Fechner were two pioneers in the study of sensory thresholds. Weber studied the smallest difference between two stimuli that a person could detect 50 percent of the time. He called this difference a just noticeable difference (jnd) and he discovered that the jnd is always a constant. For instance, if a person needs to add 5 percent more weight to notice the difference in the heaviness of a package, then this persons jnd is 5 percent. If the initial weight of the package is 10 lbs, then 0.5 lbs would need to be added to detect a difference (5 percent of 10 lb = 0.5lb). If the initial weight is 100 lbs than 5 lbs would need to be added in order for the person to detect a difference in weight (5 percent of 100 lb = 5 lb). The fact that the jnd is always a constant is known as Webers law. Fechner investigated the lowest level of a stimulus that a person could detect 50 percent of the time. He called this level the absolute threshold . Habituation and sensory adaptation are two methods our body uses to ignore unchanging information. Habituation takes place when the lower centers of the brain prevent conscious attention to a constant stimulus, such as the humming of a desktop computer. Sensory adaptation occurs in the sensory receptors themselves when the receptors stop responding to a constant stimulus, such as the feeling of your shirt on your skin. The visual sensory system is activated by light waves. There are three psychological aspects to our experience of light. Brightness is determined by the height, or amplitude, of the wave. Color , or hue, is determined by the length of the light wave, and saturation , or purity, is determined by the mixture of wavelengths of varying heights and lengths. Light enters your eye through the cornea which protects your eye and helps to focus the light, and then travels...
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This note was uploaded on 10/23/2009 for the course PSYCH 101 taught by Professor Nahad during the Fall '07 term at Ivy Tech Community College.
- Fall '07