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Lecture 12

PSC 131 Lecture 12: Sound and Hearing

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PSC 131
Geng Joy

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I. Lecture 12 – Sound and Hearing (May 17, 2017) A. Class Summary 1. What is Sound? 2. How we perceive loudness and pitch a. Amplitude and frequency 3. Anatomy and Physiology of the Auditory System a. Outer, middle, and inner ear 4. Sound Localization B. What is Sound? 1. Sounds are created when objects vibrate a. Vibrations of an object cause molecules in the object’s surrounding medium to vibrate as well, which causes pressure changes in the medium b. Traveling wave of changing air pressure (compress  decompress  compress  decompress pattern) c. Visualization: shown as a wave (change in air density) i. 761mph – speed of sound 2. Sound Waves a. What does sound look like? i. When sound is emitted, it is like a wave ii. The compression and decompression chair reaction as it travels through space iii. Similar to water ripples that move outwards b. Sound wave properties: will map on to psychological experiences i. Amplitude (how high the peaks and troughs are) = loudness ii. Frequency (cycles it goes through within a period of time and space) = pitch C. Sound Perception 1. Psychological qualities of sound waves: a. Loudness – the psychological aspect of sound related to perceived intensity or amplitude b. Pitch – the psychological aspect of sound related mainly to the fundamental frequency 2. Physical qualities of sound waves: a. Amplitude or Intensity – the magnitude of displacement (increase or decrease) of a sound pressure wave i. Perceived as loudness b. Frequency – for sound, the number of times per second that a pattern of pressure change repeats i. Perceived as pitch c. Tuning Forks i. Amplitude will change depending on how hard you hit it (loudness will change) ii. The harder you hit it, greater the amplitude will be iii. The one with a high pitch will have more change per unit sound 3. Amplitude a. Perception of amplitude is loudness (dB) b. Difference in pressure between high and low peaks of wave c. Same pure tone, different amplitudes 4. Perception of Pitch a. Measured in Hertz (Hz) – cycles per second b. Hertz (Hz) – a unit of measure of frequency; one Hz equals one cycle per second (one peak to one trough) c. Low-frequency sounds correspond to low pitches d. High-frequency sounds correspond to high pitches 5. Range of Hearing a. Human range of hearing is between 20-20,000Hz b. Our biology is attuned to a specific range of stimuli most useful to us, but that doesn’t mean it’s the only range of stimuli out there c. Ocean animals hear frequencies that are much higher than humans because of how sound travels through air vs through water 6. Human hearing uses a limited range of frequencies (Hz) and sound pressure levels (dB) a. Speech is in the middle of our range because it’s the range our ears are most protected from b. Lose sensitivity to sounds around the range as we age; speech is most robust range c. Speech has evolved over time to cater to social communication 7. Sounds of life: Frequency and intensity of noise a. Speech range is somewhere in the middle b. Other objects are on the (further down in louder range) are damaging to our ears 8. How high can you go? a. 8000 Hz; 15000 Hz; 18000 Hz; 20000 Hz b. Sensitivity will drop off over time D. Anatomy and Physiology of the Auditory System 1. How are sounds detected and recognized by the auditory system? a. Sound waves  ear canal  tympanic membrane  middle ear  inner ear and cochlear fluid  brain b. Lower sounds = slower membrane movement Higher = faster membrane movement c. A very complex system that works in reaction to vibrations that carry through to other parts and membranes of the ear d. The auditory system is very delicate e. Sounds have to travel through a lot (air, fluid) to be transmitted as signals for your brain to process 2. The Ear a. Outer ear (pinna, auditory canal) b. Middle ear (3 ossicles, ligaments) c. Inner ear (hair cells whose axons send signals) d. Cochlea, basilar hair cells = retina, retinal ganglion cells 3. Outer Ear a. The size and shape of pinnae vary greatly among mammals b. Sounds are first collected from the environment i. Structure traps sound waves and allow sounds to bounce off of pinna into auditory canal c. Head-Related Transfer Function (HRTF) – a function that describes how the pinnae, ear canals, head, and torso change the intensity of sounds with different frequencies that arrive at each ear from different locations in space (azimuth and elevation) d. Each person has their own HRTF (based on their own body) and uses it to help locate sounds i. Sound waves are funneled by the pinnae into the ear canal 4. Tympanic membrane (ear drum) separates outer from middle ear a. The eardrum – a thin sheet of skin at the end of the outer ear canal; vibrates in response to sound b. Common myth: puncturing your eardrum will leave you deaf i. In most cases, it will heal itself 5. Middle Ear: translates air waves to fluid (funnels sound wave from ear drum to oval and round window) a. Ossicles – the three tiny bones that amplifies sound since
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