chapter four book summary

chapter four book summary - Chapter 4: Sensation and...

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Chapter 4: Sensation and Perception Chapter Summary I. UNDERSTANDING SENSATION A. Processing – Transduction, or the conversion of physical stimuli into neural impulses, occurs at the receptors in the sense organs. Each sensory modality is specialized to code its stimuli into unique sets of neural impulses that the brain interprets as light, touch, and so on. Since people receive much more information at the sensory receptors than can possibly ever be processed, it is necessary to select only the information that is important, a process known as sensory reduction. Reduction is performed chiefly by an area of the brain called the reticular activating system. Here, incoming sensory information is filtered and analyzed before going to the brain where the coded information will evoke a unique sensation. B. Thresholds - The absolute threshold is the smallest magnitude of a stimulus a subject can detect. The difference threshold is the smallest change in the magnitude of a stimulus that a subject can detect. Thresholds can be affected by the process of sensory adaptation. C. Adaptation - Sensory adaptation allows people to operate efficiently in a wide range of stimulus intensities by decreasing the sensitivity to constant, unchanging stimuli. The Gate Theory of Pain is presented as an explanation of why touch and pressure can reduce pain. II. HOW WE SEE AND HEAR A. Vision - The physical stimulus for vision is light, a form of energy that is part of the electromagnetic spectrum. The wavelength of light determines its hue, or color; and the amplitude, or height, of the light wave determines its brightness. The function of the eye is to capture light and focus it on the visual receptors that convert light energy into neural impulses. The major parts of the eye include the cornea, the pupil, the iris, the lens, and the retina. All light enters the eye through the cornea which protects the eye and bends incoming light rays toward the lens. Light then enters through an opening called the pupil. The pupil is surrounded by the iris which dilates or constricts to vary the amount of light entering the eye. Behind the pupil and iris is the lens, a clear elastic structure that can change its shape to focus an image on the retina at the back of the eye. The lens thins to focus light on the retina from distant objects and bulges to focus light from near objects. The retina is the back layer of the eye that contains the visual receptor cells. The visual receptors, called photoreceptors, are the rods and cones. The rods are very sensitive to light and enable individuals to see at night. The cones are specialized for bright light conditions and enable individuals to see close and
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chapter four book summary - Chapter 4: Sensation and...

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