Chapter 4 Sensation and Perception Sensation the detection of physical energy by our sense organs which is then relayed to the brain Perception the brain s interpretation of raw sensory data Illusions happen when these two things don t match up Sensation Principles Sensory information must first go through a process known as transduction the conversion of an external stimulus into a neutral signal through sensory receptors Activation is greatest when we first encounter a stimulus then gradually declines a concept known as sensory adaptation o Ex If you are sitting on a chair for too long you begin to not notice the feeling of the chair underneath you Measuring Sensation Psychophysics the study of how we perceive sensory stimuli based on their physical characteristics Absolute Threshold the lowest level of a stimulus we can detect 50 of the trials when no other stimuli are present o Ex On a clear night our eyes can detect a single candle from 30 miles away Just Noticeable Difference the smallest change in the intensity of a stimulus that we can detect relevant to our ability to detect a quiet song vs a loud song o Weber s Law there is a constant proportional relationship between the JND and the original stimulus intensity The bigger the change needed for a change in stimuli intensity to be noticeable turning light on in a light room vs turning light on in a dark room Signal Detection Theory how stimuli are detected under different conditions o Signal to noise ratio how difficult it is to detect your signal different situations require a different response bias o Ex If you are on the phone and there is static you have to speak louder so your friend can hear you If you have a good connection however your friend can understand you without you having to raise your voice 2 Cross Modal Senses senses are not independent o McGurk Effect visual info affecting the interpretation of auditory info o Synesthesia hearing colors tasting words etc The Role of Attention Selective attention allows us to choose which sensory inputs to focus on and which to turn down like having one channel on a TV on instead of them all o The Cocktail Party Effect the ability to pick out important information from a noisy environment like hearing your name in a conversation across the room Inattentional Blindness failure to detect stimuli that are in plain sight when our attention is focused somewhere else Change Blindness failure to detect large changes in ones environment Vision Talking about light electromagnetic energy possesses a wavelength 400 blue short 750 red long How Light is emitted from a source hits an object and the reflected light is the color we see Some light is absorbed White reflects all light black reflects none Hue color shade of light Parts of the eye Sclera white part Pupil opening in center of iris that lets light in o Dilation Expansion when more light is given also when processing complex information and when we see someone we find physically attractive Iris colored portion that controls pupil size Cornea curved transparent dome that bends incoming light 3 Lens oval shaped transparent disk that focuses light rays for near or distant vision o Accommodation process in which the lenses change shape to focus light on the back of the eyes Either flat long and skinny which enables us to see distant objects or fat short and long enabling us to focus on nearby objects The shape of the eye o Cornea too steep or eyes too long myopia or nearsightedness the inability to see far away objects well o Cornea too flat or eyes too short hyperopia or far sightedness the inability to see close up objects well Retina thin membrane at the back of the eye responsible for converting incoming light to nerve impulses Fovea central part of the retina responsible for acuity sharpness of our vision o Contains 100 million sense receptor cells for vision along with cells that process visual information and send it to the brain Photo Receptors cells that change light into a neural signal o Rods enable us to see basic shapes and forms They respond to light Dark Adaptation takes about 30 minutes the time it takes for the rods to regain their maximum sensitivity for light for us to see in a dimly lit room o Cones color vision Less abundant than rods Sensitive to detail Optic Nerve contains the axons of ganglion cells that travels from the retina to the rest of the brain o Blind spot part of the optic nerve that connects to the retina part of the visual field that we can t see 4 How we perceive shape and contour Left visual field is processed by right primary cortex Right visual field is processed by left primary cortex Simple cells display yes no responses to slits of a specific orientation but these slits need to be in a certain location Complex cells are also orientation specific but they are not restricted to one location Feature Detector Cells cells that detect lines and edges How we perceive color Trichromatic Theory proposes that we base our color vision on 3 primary colors blue green and red Claims we have 3 types of cones one to respond to each color o Color blindness can t see all colors Monochromats only have one type of cone and therefore cannot see any color 5 Dichromats only have two types of cones Red green see most color but can t distinguish between reds Trichromats possess three cones Opponent Process Theory theory that we perceive colors in terms of 3 pairs of opponent cells red or green blue or yellow black or white o Explains afterimages occur when we ve stared at one color for too long and then look away and see a different colored replica of the same image When we cannot perceive visually Blindness inability to see o Causes a heightened sense of touch o This illustrates brain plasticity where some brain regions gradually take over jobs previously assigned to others Visual Agnosia deficit in perceiving objects o A person with this could tell you the shape and color of an object but can t recognize or name it Hearing Sound vibration a mechanical energy traveling through a medium o Pitch higher frequency produces higher pitch lower frequency produces lower pitch 6 o Loudness amplitude corresponds to how loud a sound is Loud sounds increased amplitude o Timbre the quality of the sound Parts of the ear o Outer Ear o Middle Ear o Inner Ear Pinna the part of the ear we see skin and cartilage flap Ear canal funnels sound waves onto the eardrum Ossicles 3 tiniest bones in the body the hammer anvil stirrup They
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