5.3 VisionLight waves cross the cornea and enter the eye at the pupil. The eye’s lens focuses this light so that the image is focused on a region of the retina known as the fovea. The foveacontains cones that possess high levels of visual acuity (cones: sensitive to acute detail, providing spatial resolution and involved in
perception of color) and operate best in bright light conditions. Rods (involved in dimly vision, perception of movement on the periphery of visual field) are located throughout the retina and operate best under dim light conditions. Visual information leaves the eye via the optic nerve. Information from each visual field is sent to the opposite side of the brain at the optic chiasm. Visual information then moves through a number of brain sites before reaching the occipital lobe, where it is processed.Two theories explain color perception. The trichromatic theoryasserts that three distinct cone groups are tuned to slightly different wavelengths of light, and it is the combination of activity across these conetypes that results in our perception of all the colors we see. The opponent-process theoryof color vision asserts that color is processed in opponent pairs and accounts for the interesting phenomenon of a negative afterimage. We perceive depth through a combination of monocularand binoculardepth cues.5.4 HearingSound waves are funneled into the auditory canal and cause vibrations of the eardrum; these vibrations move the ossicles. As the ossicles move, the stapes presses against the oval window of the cochlea, causes fluid inside the cochlea to move. As a result, hair cells embedded in the basilar membrane become enlarged, which sends neural impulses to the brain via the auditory nerve.Pitch perceptionand sound localizationare important aspects of hearing. Our ability to perceive pitch relies on both the firing rate of the hair cells in the basilar membrane as well as their location within the membrane. In terms of sound localization, both monauraland binaural cuesare used to locate where sounds originate in our environment.Individuals can be born deaf, or they can develop deafness as a result of age, genetic predisposition, and/ or environmental causes. Hearing loss that results from a failure of the vibration of the eardrum or the resultant movement of the ossicles is called conductive hearing loss. Hearing loss that involves a failure of the transmission of auditory nerve impulses to the brain is called sensorineural hearing loss. 5.5 The Other SensesTaste (gustation) and smell (olfaction) are chemical senses that employ receptors on the tongue and in the nose that bind directly with taste and odor molecules in order to transmit information to the brain for processing. Our ability to perceive touch, temperature, and painis mediated by a number of receptorsand free nerve endingsthat are distributed throughout the skin and various tissues of the body. The vestibular sensehelps us maintain a sense of balancethrough the response of hair cells in the
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