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Part III Sensation and Perception.docx

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Department
Psychology
Course
PSYC 2390
Professor
Lana Trick
Semester
Winter

Description
Sensation and Perception Notes for Final Exam 3/21/2013 9:40:00 AM Depth Perception  Tricky to get depth information because we have a 3D world (distal stimulation), but the information we receive on the back of the retina is only 2D  Proximal cue = visual angle  actual size OR how far away in depth an object is o Dimensional ambiguity Binocular Depth Cues  30% more accurate with both eyes  important for close tasks  left and right eyes have different perspectives (slightly different angles)  binocular cues rely on comparing the left and right images to determine depth o larger difference when an object is closer o look at how different left and right eye images are = binocular depth perception Can create sense of 3-dimensionality by having 2 images that are just slightly different Random dot stereograms  When you look at the images so one eye sees one side and the other sees the other, you will see a square floating over another square  Different views in different eyes; as a result, you see a square floating up How is Depth Information Derived from Stereopsis?  Solving the stereo-correspondence problem  How do I match things on one eye with the other  Need find the thing on one eye that matches with the same thing on the other eye‟s image  Find corresponding parts in left and right eye images More complicated…  Sometimes the visual system solves the “stereo-correspondence problem” incorrectly! o Error in solving the problem o Leads to an illusion of depth (they will appear either further away or much closer) o Auto-stereograms: magic eye pictures! [you can see them because of an incorrectly solved stereo-correspondence problem] Can get auto-stereograms from looking at repetitive wallpaper/patterns Retinal Disparity (a.k.a. binocular disparity)  Disparity = difference ITEMS ON THE HOROPTER  The horopter is the fixation plane = the distance away that you are focusing/fixating your eyes  Zero disparity = position of object on left and right eyes is the SAME ITEMS IN FRONT OF THE HOROPTER  Object is closer than where you are fixating  Object goes on opposite sides of the reference point (see diagram on CourseLink) = crossed disparity o e.g. both fall on temporal side ITEMS BEHIND THE HOROPTER  Object is further away than where you are fixating  Light rays fall on the SAME side of the reference point on both eyes, but at slightly different positions on each eye = uncrossed disparity o e.g. both on nasal side, but at different distances from the reference point Binocular depth is a good cue up to ~ 30 METRES There is a range beyond that where you cannot use binocular information for depth perception There is also a distance that is too CLOSE for you to use binocular information PANUM‟S FUSION AREA  Area around the horopter in which you can take the differences in information from left AND right eyes and form ONE image  If they are too far away  double images (quickly suppressed by the brain)  If they are too close  double images (more noticeable, but also suppressed) How is Stereo-depth Information Derived in the Brain?  *Interesting observation about tilt after-effect*  You can adapt one eye to left-tilted lines and then look at straight lines with your OTHER eye… and the illusion crosses over to the other eye!  One set of receptors that takes information from BOTH eyes  Receptors get tired out from looking at lines with one eye  receptors still tired when you look at straight lines with the other eye!  There are binocular cells in the brain that take information from BOTH eyes  *recall* from striate cortex (back of brain  received information from both eyes): hypercolumns (80% of cells responsive to information from BOTH eyes)  If you do single-cell recordings (wire into individual neuron), you will find disparity-sensitive cells = respond differently depending on HOW DIFFERENT images are in left and right eyes o e.g. there are cells that respond best to 30 minutes of arc (vs. 0 minutes or 15 minutes or 45 or 60)  looking for a particular depth!  respond better to one depth than others  Bottom line is that, just as there are some cells that respond best to a certain orientation, there are cells that respond best to different disparities (e.g. different depths; crossed or uncrossed disparity, etc.)  Binocular cells will not develop unless you have certain kinds of experiences during critical periods  Critical periods = when a baby is developing, he/she must get certain kinds of stimulation in order for different processes to develop properly  Studies on kittens  kittens are born blind  4 weeks  4 months = critical periods  Must have certain visual experiences in order for binocular depth perception to develop properly Kitty Pirate Studies  On one day, they patch up the left eye (some time during critical period); on next day, they patch up the right eye (and back and forth)  Never get stimulation of left and right eyes simultaneously  Don‟t develop proper depth perception (in particular, don‟t develop BINOCULAR depth perception)  If you do this to a cat after 6 months, nothing happens  If you do it during the critical period, striate cortex does not develop binocular cells Human Babies  Children born with strabismus = imbalance in eye muscles  Can cause a person to be cross-eyed OR wall-eyed  Cannot match images in left and right eyes because images are TOO DIFFERENT  Results in “Binocular Rivalry”  eyes are seeing 2 VERY different things.  Brain will suppress one of the images to avoid this “rivalry”  If not corrected early enough, child will not develop proper binocular depth perception or binocular cells in striate cortex  Must be corrected by surgical procedures If there are no binocular cells, the tilt after-effect will NOT transfer from one eye to the other as shown earlier! Way of determining if surgery was done on time! Coordination is very difficult without binocular depth perception  This is why binocular stimulation is crucial during critical periods of development CHESHIRE CAT ILLUSION  Binocular Rivalry o Look at friend with blank wall on right side o Angle mirror toward blank wall (on nose) o Brain will quickly suppress “boring” image, and all you will see is your friend o Wave fingers in front of mirror (motion is a high-priority stimulus)  visual system gets confused, so you will see your fingers waving through your friend‟s head The Constancies  Related to how it is that an object can be seen as constant in size when its visual angle changes depending on how far away it is (visual angle occupied by object is changing) SIZE CONSTANCY  ability to see something as the same size even though the visual angle occupied by the object changes  Achieved by the visual system factoring in the distance away  Takes in depth information in light of depth cues  Can result in systematic errors ILLUSIONS BASED ON MISPLACED SIZE  Ponzo Illusion (see railroad picture)  Interpret visual cues to see the object in the “distance” as further away and therefore MUCH bigger than the close object  Visual system factors in depth information from picture, even though it is a 2D image Moon Illusion  Again, based on misplaced size constancy  Moon looks larger on the horizon  When you look over the horizon, you have lots of depth cues that say the horizon is far away  When you look straight up, there aren‟t many depth cues (therefore sky looks closer than horizon BECAUSE of the lack of depth cues) After-image changing size  Burned out part of retina stays same size  Looks larger if you look in distance (further away) because of depth cues; looks smaller when you look at a close piece of paper (no depth cues) OBJECT PERCEPTION  Organizing given information into objects (grouping together things that go together)  seeing objects as wholes o Grouping together information from all rods and cones (contours, shades, etc.) to see objects as whole objects  Each rod and cone only knows about a tiny point of light  Doesn‟t know anything about what its neighbours are doing  Cells may not know if they are receiving light from the same object! OBJECT RECOGNITION  When you recognize an object, you look at it and know that you have seen it before  Take information from retina and then match it to a memory from long-term memory (e.g. what a cat looks like)  Key to intelligent visual behaviour  e.g. bitten by big, black, furry thing one day  next time you see a big, black, furry thing (or something similar), recognize that it bit you and stay away (even if you don‟t know the name for it) Biederman Machine – random object  can‟t name it, but you can recognize it later! VISUAL-MOTOR COORDINATION  Must see the object as a whole to avoid it, manipulate it, touch it, work with it, etc. 2 Approaches TOP-DOWN  Stress importance of pre-existing knowledge  Past experiences drive what it is that you see  Take cues from what is around it (previous knowledge) to recognize something in context  e.g. B and 13 can look very similar, but you can recognize which is which based on what is around them (e.g. A and C vs. 12 and 14) Perceptual Set  See images based on what you were prepared to see o Prepared to see something based on previous experiences/beliefs/etc.  Can‟t be entire story  if we only saw what we expect to see, we would die (or an animal would die) BOTTOM-UP  Information from right off the retinas  Can‟t afford to ignore this information, because sometimes we don‟t expect to see things, but they ARE there! (Important for survival) Way to Organize Information from Textbook (all independent theories – no apparent linkage) 2 TYPES OF PROCESS  Spatially Parallel Process (pre-attentive) o [Everywhere, at the same time] o pre-attentive o does not require attention (happens automatically) o *Looking for particular colours/shapes/orientation ALL over picture*  Spatially Serial Process (attentive) o [Everywhere, ONE THING at a time] o Process one part of image, but not the rest o Attention paid to one area of an image (like a spotlight)  lots of information (FOCUS) o In areas surrounding, not much information is perceived  **You can be looking at something but NOT paying attention**  ***You need not be conscious of the things in our visual field*** 3 STAGE MODEL OVERVIEW First = Low Level Vision (Pre-attentive Analyses)  Spatially parallel  Pre-attentive Second = Visual Routines (Analyses requiring Spatial Attention)  Spatially serial Third = Visual Cognition (Object Recognition)  Match visual image with a long-term memory  recognize the object, name or no name (regardless); at least know that you‟ve seen it before STAGE 1 (LOW LEVEL VISION – PRE-ATTENTIVE)  Get information from retina  Find discontinuities (places side-by-side that are different in terms of brightness, colour, etc.)  these are the edges of objects  The entire visual system relies on discontinuities  Ganzfeld = ping pong balls over eyes  see even white surface with no edges (can do the same if you close your eyes) o After a while, you‟ll start to see little flashes of colour (eyes start malfunctioning) o Longer still and your eyes will start moving independently and unconsciously (eyes need contours to anchor where eyes are!) o Without contours, the visual system can‟t work!! Stabilized Image Technique  Image moves with retina  if there was a contour, it would always fall on the same part of retina, regardless of how you move your eyes  If it does stay on the same part of the retina like this, it eventually disappears because there is NO CHANGE **Need contours AND change** Registering these contours takes a certain amount of time  Know this because of masking studies  Dot shown for 20 ms = all you would see is the dot  See dot for 20 ms followed (less than 100 ms later) by the mask (dark everywhere BUT the spot) = see large black dot the size of the mask [sum of 2 images]  Dot for 20 ms followed (between 100 and 200 ms later) by mask = all you would see is the mask  Dot for 20 ms followed (MORE than 200 ms later) by mask = see dot first and then see mask second [correct representation of images] *rushing the visual system may cause the images to be put on top of each other, or the first image forgotten altogether* CATEGORIZING THE DISCONTINUITIES  How big? What colour? Line orientation?  Visual Search Task  o Decision of if there is or is not the desired discontinuity does NOT change with more/fewer other discontinuities to sort through (e.g. looking for red line within black lines; horizontal line within vertical lines, etc.) o Response time is same regardless of number of discontinuities  Difference in feature (e.g. colour, orientation, etc.) = pop-out (can find the object regardless of the number of other things present) o Time to find target is independent of how crowded the visual field is GESTALT GROUPING PRINCIPLES [still in first stage  spatially parallel]  Whole is different than the sum of the parts  Important for the study of object perception  requires grouping of discontinuities to see object as a whole  Grouping by Proximity o Groups in such a way that things that are close together are perceived as belonging together o Group things that are closest together if given a choice  Grouping by Similarity o Similar in terms of features (e.g. colour, shape, orientation, etc.) o Tendency to see similar things as belonging to a group  Grouping by Good Continuation o Visual system is looking for continuous lines if they can be found o Likes to group items that are continuous (rather than starting and stopping)  Grouping by Closure o Visual system looking for closed figures (e.g. a box or a triangle, etc.)  Grouped by Connectedness o If objects are touching, we assume they are part of the same thing (or they ARE the same thing) EFFORTLESS TEXTURE SEGREGATION  Size, orientation, colour, lightness/brightness  Some distinctions are easier to make than others (e.g. hard to see differences between L and T, but not between two different orientations of T) FORMATION OF ILLUSORY CONTOURS AROUND LINE  Group discontinuities to make an object appear (e.g. circles with cutouts that look like the skeleton of a cube)  Visual system LOOKING for continuous lines  Can read words even if parts of letters are covered  Kanizsa triangle (see triangle that isn‟t actually there) Determining What is FIGURE and What is GROUND  e.g. vase vs. 2 faces  Interpretation of image is based on decision of where the contour belongs! (if it belongs in the middle, you see the vase… if it belongs on the outside, you see the faces)  What you decide is the FIGURE is the thing that you remember STAGE 2: Visual Routines (analyses requiring spatial attention)  There are some situations when you cannot look at *everything* at once (e.g. looking for a friend‟s face in a crowd)  Another example: Where‟s Waldo books o The more figures there are, and the larger the area, the longer it takes to go through it Spatial Relations Between Parts (of an object)  e.g. all the parts of a face could be present, but if they are not in their “correct” places, it may not be recognizable as a f face (e.g. eye above and on each side of nose, mouth below nose, etc.) o Inside/Outside o Left/Right o Connected to/Not connected to  e.g. difference between b,p,d, and q (all same components, but must analyze spatial relations to figure out which it is!) “Conjoining” Different Features  It is both black and vertical? (colour and orientation)  Look at visual search task  when you do a visual search task and items differ in terms of spatial relations (or a combination of features), it takes longer as the number of items increases o If it is just one feature you‟re looking for, time doesn‟t increase as the number of items increases o If it is a combination of features (or spatial relation) that you are looking for, the response time increases as the number of items increases o Where‟s Waldo involves looking for a combination of features AND a spatial relation  very complicated search task Object File  Information about object  e.g. for a green letter “d” o green o vertical line o circle o circle right of line o circle on the bottom o etc.  Once you build an object file, you can recognize objects in the rd future (and go on to 3 stage)  Once you‟ve build the object file, it stays with the object (so even if one feature changes, you can still recognize it based on it‟s other features PROBLEMS THAT CAN OCCUR  Illusory Conjunctions o Not enough time to properly attend to object [or too tired] o Causes you to see very strange things that you would not otherwise see o Can cause problems with eye witness testimony o People can be VERY sure they saw something  in a very emotional/violent/distressing situation, your attention is on whatever caused the situation to be that way (e.g. a gun being waved around), and problems occur later when trying to identify the assailant because their attention way focused elsewhere and so features from other people around can “float” on to the assailant because your focus was not on the person! o Things you are *not* focusing on can get muddled with features of other objects nearby  Integrative Agnosia o Inferotemporal Cortex (IT)  damage here causes agnosia [TEMPORAL AREA DAMAGE] o Integrative agnosia causes difficulty in making object files (e.g. man who mistook wife for a hat saw different features but was not able to recall/form object files in order to identify his wife as his wife!) o If someone with this kind of agnosia were to draw a man, he/she would draw all the parts, but they would not have appropriate spatial relations to each other (e.g. all parts of the face might not be on the face, or anywhere near the head, for that matter)  Simultagnosia (Balint‟s syndrome) o Parietal problem, in addition to temporal damage o No problem seeing one object at a time o Problems arise when there are many object (trouble seeing object in context of other objects) o If there are many objects, they get the parts all mixed up! STAGE 3: Visual Cognition (object recognition)  Space is no longer relevant (since you already have the object file)  Matching object file to long term memory!  You can name it, or at least recognize that it is familiar Some people with certain kinds of agnosia can form an object file, but can‟t match it! Some people can tell you about the way something looks (long term memory representation), but cannot tell you what‟s right in front of them! (Again, trouble matching) MOVEMENT PERCEPTION (Chapter 8) Some animals don‟t have very good depth perception, but EVERY animal has good motion perception Motion perception = ability to see movement IMPORTANCE?  Motion is important because motion can define objects  can define object form  Called grouping by common fate (Group together things that move together) [last Gestalt grouping principle]  Allows you to define objects by looking for things move together (same speed, direction, etc.)  Animals freeze to hide themselves (camouflage)  if they move, they are more visible o obviously only if the colours are appropriate to hide the animal Random Dot Kinematogram  Even if they are just random dots, seeing certain dots move together will cause you to see them as an object/as a whole GROUPING IN 3D  Kinetic Depth Effect o When you start rotating a wire cube, you no longer see it as a square, but it causes you to see it in 3D o Cause you to see things in 3-dimensions (while they are still, they look 2D)  [also includes Ullman‟s Structure from Motion Displays]  Johansson Figures o All in black with lights on joints o Go in all dark room  when you are still, you look like a bunch of lights, but when they start moving you can tell it is a person, whether it is male/female, etc. [you can use motion to identify what a creature is!] o (we have a bias toward seeing things as human) o Biological movement can allow us to tell even different human apart (e.g. your movement from that of your friend‟s from that of your mom‟s, etc.) MOTION & VISUAL-MOTOR COORDINATION  Depth Cues (review) o Motion is important in understanding how far away things are o Motion is important in defining depth o Also important in balance (vision very important for balance  e.g. standing on one leg with eyes closed) o Movement is particularly important for understanding where the body is in space  Optic Flow o Blurring when looking out car window o Blurring of objects across visual field = object flow o Optic flow used in movies to make viewers feel like they are part of the action o Optic flow very important for balance…  Swinging Room Experiment o Done using babies o Put baby in a room o Walls were not connected to floor  able to swing back and forth o Made walls swing toward baby o When walls swing toward you, give you optic flow (brain thinks you are falling forward; over-compensate and fall backwards – vice versa with wall swinging away) How do you know when something is going to hit you?  Look at rate of change in object size  As something is approaching you, it gets larger and larger, and there is a sudden increase in rate of change of size as it gets *very* close (causes you to flinch) REAL MOTION VS. APPARENT MOTION  Cannot tell the difference  When you watch movies (motion pictures), you are seeing a bunch of still pictures in rapid sequence and you see an illusion of motion)  Also, flip books give the illusion of motion which we interpret as something moving (even though it‟s not) Rules for Apparent Motion  When do you see motion, and when don‟t you?!  All has to do with timing  If you see a dot in one corner, and then less than 30ms later you see a dot in the opposite corner, you see two dots in the same frame/image  If you see a dot in one corner, and then 60 – 200ms later you see a dot in the opposite corner, you will see movement  If you see a dot in one corner, and then more than 200ms later you see a dot in the opposite corner, you see two them as two separate things 2 SYSTEMS  Image-Retina System o Relies on there being changes in the image on the retina o Watching a waterfall – stare at water going down for a long time, then look around at other things, and everything will look like it‟s going up! o Related to after effects (tiring out receptors that are sensitive to downward motion)  Eye-Head System o When we look at objects and they are moving, often we track them with our eyes o e.g. tracking mouse as it scurries  mouse stays on fovea (no change in position of image on retina), but still see it as moving o Aubert-Fleischl Effect  compares how quickly something is moving as judged by the two systems individually  Person looks at moving pendulum (quite quickly)  Have them follow it with their eyes  judge speed  Second time, keep eyes still  judge speed [pendulum seems to be moving a little faster than when you were tracking it]  Head-eye system can‟t always keep up when trying to track things [underestimate how quickly an object is moving]  If you keep your eyes still, you get a more realistic idea of how quickly things are moving How Visual System Gets Direction Sensitivity out of Neurons  6 neurons (A – F)  each neurons hooks up with intermediary neuron (all excitatory inputs)  3rdlevel = motion detector  A, C, and E will have excitatory inputs  B, D, and F have inhibitory inputs to A, C, and E respectively  shows motion (RIGHT TO LEFT) because when the object is at B, D, or F, they try to inhibit A, C, or E respectively, it is too late since A, C, and E have already been stimulated  If moving (LEFT TO RIGHT) inhibition and excitation meet at intermediary cells, so no action potential sent to motion detector o (could be the opposite, depending on set-up)  Shows how you can get something that sees direction of motion just from neurons RETINA  Takes message out the back of the eye  Magno cells specialized for MOTION  Transient response  if an object stays in one place, the magno cell stops responding  Perception of change TECTO-PULVINAR SYSTEM (SUPERIOR COLLICULUS)  Very important in eye movements  Cells respond if eyes are stationary, some just as they are about to move, and others when eyes are moving  receives ONLY magno fibers  Important to head-eye system and tracking STRIATE CORTEX  Respond to certain features/attributes (simple cells vs. complex cells vs. hypercomplex cells)  Waterfall illusion is caused by striate cortex  Part of image-retina system  image must be moving on the retina Disco  strobe light (see people as dancing in freeze frames  principle behind apparent motion (images more than 200ms apart) Kitty in disco study  brought kittens up in an environment with strobe lights  did not develop motion sensitive cells (in visual cortex)  can only develop if you see moving things (normal environment) MEDIAL TEMPORAL CORTEX (MT)  Involved in motion perception as well  Unrelated motion  little cell response  Some relation/correlation in motion  more cell response  Cells respond based on how cohesive motion is  Looks at more global motion (looking for consistency in motion) MEDIAL SUPERIOR TEMPORAL CORTEX (MST)  Involved in seeing motion in depth (looming)  Can be stimulated by a moving spiral SUPERIOR TEMPORAL SULCUS  Involved in object recognition  Combines motion perception and object perception (esp. recognizing biological motion  recognizing something by the way it moves) V3  Distinguishing between different kinds of motion (esp. actual vs. apparent motion) Problems in Motion Perception  Induced Self-Motion Illusion  sitting in train and train beside you starts to move, you feel like you‟re moving as well o also called Vection o e.g. looking at moon and clouds are moving very quickly, but it looks like the moon is moving  visual system is having trouble deciding what is moving!  visual system is making assumption that the small thing is more likely to move (lots of illusions based on this assumption)  visual system UNDER-estimates speed of LARGE things COROLLARY DISCHARGE THEORY  Motor cortex signals eye muscles to move  When you choose to move your eyes, not only do you send a message to your eye muscles, but also to the comparator (area in the brain that makes a comparison)  Corollary = copy  Send a copy to another part of the brain so you know you are moving your eyes to the left/right  Sensory signal from retina = image movement signal o when something shifts from one place to another on the eye, a message is sent to the comparator  Comparator receives information about 1) eye movements AND 2) whether things are shifting position on the retina (image movement signal)  Comparator sends message to the visual system Theory that explains how you know the difference between real world object movement and when an image is just shifting position on your retina (changes occurring in the retina)  ** If the comparator receives ONLY the sensory signal, this means the object is moving (e.g. NO eye movement)  ** If the comparator ONLY receives the corollary signal (copy of motor signal), this ALSO means the object is moving (because the object stays in the same place on the retina, but the eyes are moving = tracking an object)  ** If you get BOTH signals simultaneously, it is interpreted as your moving your eyes which make things LOOK like they‟re moving when they actually are not For an after image, the burned out part in your retina stays STATIONARY, but your eyes are MOVING … therefore you see the afterimage as moving around! Curare  blocks action of acetylcholine  Study done to see if you needed to make an eye movement to get the perception of movement, or was it enough to just make the INTENTION of moving the eyes  Gave himself curare, paralyzing him  (Kept alive in iron lung)  Formed the INTENTION to move his eyes (couldn‟t actually move them because he was paralyzed), but the INTENTION was enough to make the object look like it was moving  Even the intention of moving the eyes will make it look like the object is moving! The stimulus for hearing is SOUND Sound is MECHANICAL ENERGY = when molecules push up against other molecules (when molecules bump together) (e.g. hitting a blackboard  sound travels because air molecules hit each other and some of them go into your ear and cause the ear drum to go back and forth) Guitar String:  Waves of compression and rarefaction o (similarly with old-fashioned stereo speaker) **Need molecules (a medium) for the whole auditory system to work** Wave of compression = pressure goes up (molecules closer together) Wave of rarefaction = pressure goes down (molecules more spread out) SINE WAVES (simplest kind of wave) Amplitude = height from mid point to peak or to trough  volume [larger = louder]  Sensitive to 10 million DIFFERENCES in intensity (or amplitude)  0.0002 dynes/cm^2 ------- softest sound we can hear  dyne = force needed to move 1 gram at an acceleration of 1 cm/sec/sec  F = ma Very sensitive to soft sounds  Decibel (dB) = 20 log (actual intensity of sound / intensity of the quietest/softest sound we can hear)  Quietest sound we can hear = 0.0002 dynes/cm^2 Logs  a way of condensing/compression units (needed to compress a range of 10 million into a more usable scale) Frequency = how many waves occur per second  corresponds to pitch (how high or low) – [high pitch = high frequency]  Measured in Hertz (Hz) = cycles/second  Lowest possible note on a piano = 27.5 Hz (27.5 sound waves / second)  Highest note = ~4000 Hz  **Sound travels faster in water because molecules are closer together** o Cats, bats, moths, mice, and dogs can hear higher frequencies than we can o Elephants can hear lower frequencies than we can Timbre = related to complexity of the sound wave (most are NOT simple sine waves, but complex waves)  QUALITY of sound  Instrument that can produce a wave CLOSEST to a sine wave = a flute  Mixture of different frequencies  sum of different frequencies and intensities  Fourier analysis  ear takes the sound apart into its various components (just as with light) o This is why people‟s voices sound different Phase = At what point on a sound wave you are Phase angle  where you are on the sound wave 0 degrees = beginning of cycle at normal air pressure 90 degrees = top of compression 180 degrees = back to normal air pressure 270 degrees = bottom of rarefaction 360 degrees = end of a complete cycle (normal air pressure) HOW SOUND INTERACTS WITH THINGS  Objects o Objects reflect sound back o In an “anechoic chamber”, no sound is reflected back o Some objects absorb sound (e.g. carpet absorbs about 20% whereas plaster/tile absorbs about 3%) o Some objects also resonate sound  objects start to vibrate in sympathy to the sound  e.g. if you play a piano right beside the guitar, the string (same one as the note you are playing) will begin to vibrate  Some people can shatter glass with their voices  Produce sound that causes crystal to vibrate (must be at resonant frequency)  You can vibrate at your resonant frequency as well at a really loud concert  e.g Tacoma narrows bridge  Soldiers are told to march out of time on bridges to avoid the risk of causing it to vibrate at its resonant frequency and vibrate itself apart So three main possibilities: reflect, absorb, or resonate Other Sounds  (1) Sounds can reinforce each other (if they are identical, they will ADD together)  (2) Sounds can also cancel each other out (same exact frequency, but opposite phase  silence) = active noise cancelation o You can have dead zones in a concert hall because a sound and its echo *can* cancel each other out!  (3) Sounds can *sometimes* reinforce and *sometimes* cancel o If instruments are NOT in tune, you will get the sound of alternate reinforcement and cancelation = BEATS (e.g. 1000 Hz and 1004 Hz) FUNCTIONS OF THE EAR (1)Gathering sounds (2) Amplify sounds  Sense of hearing was first developed in ancient fishes  Lateral line = line of nerve cells (hair cells) that moved when the water moved  Moved that whole hair cell model into the interior of our ears  In the cochlea, there is fluid that moves around and causes hair cells in our inner ear to move (causing neural impulses) o PROBLEM: takes less force to make a sound in air than in water (lose about 30dB of intensity) o Intensity of sound must be INCREASED before it reaches inner ear so it is powerful enough to move fluid and matches outside stimulus  hence the amplification (3) Transduction  Changing energy from mechanical energy to electrical energy understood by neurons  Frequency analysis = find component frequencies for complex sound Physiology of the Ear  Outer Ear o PINNAE – flap on outside [Sound Localization]  For gathering sound  Some animals can point their pinnae in the direction of the sounds  Shape of interior of pinnae have a role in letting you know where the sound comes from  Holes (grooves) bounce sounds differently depending on the kinds/directions of sounds  Each person has *unique* pinnae (so if you swapped pinnae with someone, you would both have trouble figuring out where sounds were coming from) o AUDITORY CANAL [Amplifies Sound]  2.5 – 3 cm long  Protects inner ear from cold, foreign objects  Has wax in it (to prevent *stuff* from getting in the ear)  Causes resonance (due to its length)  Resonates to certain frequencies  amplifies human speech frequencies!  Resonant frequencies determined by length of canal o EAR DRUM  Delicate membrane that vibrates when there is a sound  Thin chunk of VERY sensitive skin Problems and Disorders  Plugged Ear Canal o Stick things in the ear canal o Can get plugged by too much ear wax built up  Swimmer’s Ear o Water gets trapped in auditory canal o Fluid gets warm (due to heat of body)  perfect environment for bacteria to grow o Bacteria causes ear canal to swell o Painful, itchy, uncomfortable  Broken Ear Drum o Loud sounds (e.g. an explo
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