Chapter 4 Modules 10 11 12 Module 10 Sensing the World Around Us 02 19 2012 Sensation is the activation of the sense organs by a source of physical energy Perception is the sorting out interpretation analysis and integration of stimuli carried out by the sense organs and brains Stimulus is any passing source of physical energy that produces a responses in a sense organ vary in type and intensity different types activate different sense organs Psychophysics the study of the relationship between the physical aspects of stimuli and our psychological experience of them Absolute thresholds Detecting What s Out There Absolute threshold is the smallest intensity of a stimulus that must be present for it to be detected Noise the background stimulation that interferes with the perception of other stimuli Difference Thresholds Noticing Distinction Between Stimuli Difference threshold the smallest level of added or reduced stimulation required to sense that a change in stimulation has occurred the minimum change in stimulation required to detect the difference between 2 stimuli just noticeable difference Weber s law states that a just noticeable difference is a constant proportion of the intensity of an initial stimulus rather than a constant amount Sensory Adaptation Turning Down Our Responses Adaptation an adjustment in sensory capacity after prolonged exposure to unchanging stimuli Module 11 Vision Shedding Light on the Eye Visual spectrum range of wavelengths that humans are sensitive to eyes convert light to a form that can be used by neurons that serve as messengers to the brain Illuminating the Structure of the Eye Light travels through the cornea transparent protective window Cornea refracts light as it passes through focusing it Light transverses the pupil dark hole in the center of the iris the colored part of the eye Size of the pupil depends on the amount of light in the environment dimmer larger pupils Enters the lens directly behind the pupil bends the rays so that they are properly focused on the rear of the eye changes thickness through accommodation Reaching the Retina o Retina electromagnetic energy of light is converted to electrical impulses for transmission to the brain consists of a thin layer of nerve cells at the back of the eyeball Rods thin cylindrical receptor cells that are highly sensitive to light Cones cone shaped light sensitive receptor cells that are responsible for sharp focus and color perception particularly in bright light Distributed unevenly throughout the retina Cones are concentrated in the fovea sensitive area the is used to focus Responsible for dark and light adaptation Sending the Message from the Eye to the Brain o Rods contain rhodopsin a complex reddish purple substance whose composition changes chemically when energized by light o Stimulation of the nerve cells in the eyes triggers a neural response that is transmitted to other nerve cells called bipolar and ganglion cells o Optic nerve bundle of ganglion axons that process information collected by ganglion cells o Neural impulses move through the optic nerve and meet at the optic chiasm where each optic nerve then splits o Image to the person s right eye is sent to the left side of the brain and the image to the person s left is transmitted to the right side of the brain Processing the Visual Message o Ganglion cells gather information from a group of rods and cones in a particular area of the eye and compare the amount of light entering the center of that area with the amount of light in the area around it o Ultimate processing takes place in the visual cortex of the brain o Feature detection cells are activated only by lines of a particular width shape or orientation o Brain s integration of visual information does not occur in a single step or location but a process the occurs on several levels simultaneously Color Vision and Color Blindness The 7 million color spectrum Range of wavelengths that we can see are relatively narrow but we can distinguish no less than 7 million different colors 7 of men and 0 4 of women are color blind Explaining color vision o Trichromatic theory of color vision there are 3 kinds of cones in the retina each which responds primarily to a specific range of wavelengths one is most responsive to blue violet colors one to green and the third to yellow red but doesn t explain afterimages o Opponent process theory of color vision receptor cells are linked in pairs working in opposition to each other blue yellow pairing red green pairing and a black white pairing explains afterimage Module 12 Hearing the Other Senses Sensing Sound Outer ear acts as a reverse megaphone designed to collect and bring sounds into the internal portions of the ear Sound localization the process by which we identify the direction from which a sound is coming Sound the movement of air molecules brought about by a source of vibration Auditory canal a tubelike passage that leads to the eardrum The Physical Aspects of Sound Eardrum aptly named because it operates as a miniature drum vibrating when sound waves hit it Middle ear a tiny chamber containing three bones hammer anvil and stirrup that transmits vibrations and increases strength to the oval window Inner ear the portion of the ear that changes the sound vibrations into a form in which they can be transmitted to the brain Cochlea a coiled tube that looks something like a snail and is filled with fluid that vibrates in response to sound Basilar membrane inside the cochlea is the basilar membrane a structure that runs through the center of the cochlea Hair cells cover the basilar membrane are bent by the vibrations entering the cochlea the cells sends a neural message to the brain Sound is the physical movement of air molecules in regular wave like patterns caused by vibrating source Frequency the number of wave cycles that occur in a second Low pitch low frequency high pitch high frequency Amplitude feature of wave patterns that allows us to distinguish between loud and soft sounds Place theory of hearing states that different areas of the basilar membrane responds to different frequencies Frequency theory of hearing suggests that the entire basilar membranes acts as a microphone vibrating as a whole in response to a sound Vestibular system which responds to the pull of gravity and allows us to maintain our balance Semicircular canals main structure of the vestibular system consist of 3 tubes containing fluids that sloshes when the head
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