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Lecture 6

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Psychology 2115A/B

Lecture Six 10/3/2012 11:25:00 AM Audition cont’d The basilar membrane  Has motion that reflects a traveling wave  Reaches a peak and then will die off  High frequency’s peak quickly and sharply  Low frequency’s travel farther down the membrane and there peaks are not as sharp  This allows us to hear because it moves the organ of corti  Pull the hairs- they are connected Equal loudness contours  We hear the sounds that are most important to us  Threshold of frequency intensity required for identification  People were given a tone (say 5000 hertz tone) and then were given a second and were asked to try and match the two tones by adjusting the second to one to match the first. o Shows that you need to increase the intensity for the second one to sound as loud as the first  Contours are the same as the threshold  The frequency’s we don’t like, we don’t hear well  The ones that we do like, we do hear well  For the curve, they are just adjusting the loudness  Normal conversation is around 60 decibels  Stevens power law works – the exponent is around .60 Pitch  Baby can hear pitch extremely well 20 hertz-22000 hertz o You lose this over time How do we perceive different pitches?  Do basic theories o 1. Place theory  back to the 1800  Helmholtz said each pitch you perceive is on a different spot on the basilar membrane  Von Bekesy: created a model of how the basilar membrane might work  There is a place on the basilar membrane were each pitch will reach its maximum (not just one place like Helmholtz said)  2. Frequency theory (Von Bekesy) o said that 1000 hertz = the basilar membrane will vibrate 1000 times per second also causes the auditory nerve to fire 1000 times per second o turns out the auditory nerve does fire the same as the frequency of the tone (1000 hertz = 1000 fires) how can we run an experiment that only carries place stimulation and frequency stimulation?  White noise: that buzz sound from a radio, it has all the frequencies in it (key in these experiments). White noise is soothing  Experiment 1: how can we create an experiment were they determine frequency: NO PLACE INFORMATION o Get a white noise generator and pulse the white noise (1 millisecond whit noise, 1 millisecond quiet) o White noise: every place on the basilar membrane is vibrating o Stimulus: 500 pulses per second o This means that it activates every place on the basilar membrane, allowing you to look at frequency o Do you hear a 500 hertz tone because the membrane is vibrating 500 times per second?  Yes, you will hear a 500 hertz tone  Experiment 2: how can we create an experiment were they determine place: NO FREQUENCY INFORMATION o Play only frequency’s between 1 and 1000 hertz, one are of the basilar membrane will be very active and some other places wont be o When you turn of the tone that places that were not as active will not be as fatigued o What happened:  Presented white noise for about half a minute to fatigue the membrane- but there is a gap in frequency’s (ex leave out 999-110)  Stop the noise  Everywhere on the membrane was activated except for the part that was missing  This part will not be as fatigued  The parts that were activated, there activation goes way down  The part of the membrane that wasn’t stimulated is more active now that there is no noise – place information is being sent to the brain because it is having more spontaneous information o This means that the brain will hear the sound that was missing because it is now highly active (you hear the sound)  Results, you will hear the sound that was missing in the experiment  ** remember the after image will not last long (the noise you hear after the actual white noise) it will last about thirty seconds  when you put multiple frequency's together there is a summation of the frequency’s  if you play two sounds that are very close in frequency (1000, 1001) and you graph them for 1 second, when you summate the two curves, there is a point were they will cancel themselves out  (1000, 1002) – these will cancel out at two points  much over three difference you wont hear it  these silences are known as beats Vision 10/3/2012 11:25:00 AM  the stimulus is electromagnetic radiation: light  people think of light as a particle and a wave  high frequency’s short wave lengths  low frequency’s long wave lengths Light waves  We don’t perceive all wave lengths  You perceive the visible spectrum o 380nm-760nm (nanometers) o (billionths of a meter)  below 380 (ultraviolet, x rays)  above 760 (infrared, radio)  doesn’t matter that we cant see these waves, they aren’t solid  the stuff that we see, are the wave lengths of solid objects (the things that matter, don’t want to walk off a cliff or into rocks)  the source of light waves is the sun- gives off white light (has all the wave lengths). White light can be decomposed (prism, splits the wave lengths giving off the rainbow o ROY G BIV  Perception of colour is tied to wave lengths Intensity of the light stimulus  Photometer: point it at a light and will give the intensity  When you do this you are measuring the radiance of the light in lumens  When you want to measure the light that reaches and object (light to a table) you are measuring the illuminance D^2 (distance squared)  Luminance: a measure of light coming from a non light source o Example the light sends light to the desk, and then the object projects the light off into the environment allowing you to see the desk  The reflectance ratio: luminance over the illuminance o Bright to the eye: high ratio (example chalk) o Things that are dark to the eye: the object absorbs the light and has a low ratio (example black cabinet)  The retinal illuminance: how much light gets to your eye o This will vary with distance (people closer to the object will get more light then people farther away) The eye  The cornea: the front of the eye. Its there for protection, and helps with focusing (a little)  The pupil: black, gets smaller with bright light and larger with minimal light. You don’t want bright light hitting the back of the eye, so the pupil shrinks to protect the back. It also helps focus (smaller focused more, becaus
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