PSYC 3040 Heaing

What is a sound?

What is a sound?

Two answers:

Physical (pressure changes)

Perceptual (subjective experience of hearing)

Sound Waves

Physical part of sound

Create vibrations in the air that make sound

How do speakers work?

Alternate between pushing air together (condensation) and pulling air apart (refraction) to make repeating patterns of low/high pressure air

Frequency

Number of cycles within a given time period

Pitch

Perception of frequency, how ‘high’ a sound is

Higher frequency means higher pitch

Average Human Hearing Range

20Hz - 20,000Hz

What does a dog whistle do?

Makes a frequency too high for humans to hear, but dogs can hear it and it’s very unpleasant

Amplitude

Difference in pressure between the high peaks and low troughs of a sound wave

measured in dB

Loudness

The subjective experience of intensity

Same dB level gives different subjective loudness for different frequencies

Higher amplitude means louder

How does frequency affect loudness?

loudness gets lower towards edges of perceivable frequencies

Extremely high or low frequencies are quieter

Presbycusis

Hearing Loss

Greatest loss at high frequencies

A little worse in men than woman

Are sounds in the real world made of one frequency?

NO. Sounds are combinations of many frequencied

What makes a periodic tone?

Pure sounds (just one frequency) or complex sounds with multiples of the same frequency

Fundamental Frequency

First pitch in a series of multiples

Perceived Pitch

First harmonic is implied, even if only the 2nd 3rd or 4th harmonics are present

Timbre

All other perceptual qualities of a sound besides loudness, pitch, and duration

(what makes a trumpet sound different than a flute)

Thee subdivisions in the ear

Outer, middle, and inner ear

Outer Ear

Has Pinna and Auditory Canal

Pinna

What we see as an ear, helps identify sound locations and magnify certain frequencies

Auditory Canal

Tube-like 3cm long

Protects tympanic membrane at the end of canal

helps to amplify frequencies between 1,000 and 5,000 Hz (human speech)

Tympanic Membrane

Part of middle ear

aka the ear drum

membrane that vibrates back and forth when hit by sound

three ossicles

Malleus, Incus, and Stapes

Why are the ossicles necessary?

They amplify the vibrations for better transfer through the cochlear fluid in the inner ear

How can the middle ear dampen sounds?

Middle ear muscles work to dampen ossicles vibrations to protect inner ear

Cochlea

Fluid filled, snail like structure in the inner ear that is set into vibration by the stapes

Organ of Corti

Are in the cochlear partition that contains auditory receptors

Basilar membrane

In organ of corti

Vibrates in response to sound

Contains inner and outer hair cells which function as receptors for heading

Tectorial Membrane

Slides back and forth along the basilar membrane to trigger hair cells

What causes auditory nerve fibers to fire?

Cilia (hair) bend in response to movement of organ corti and tectorial membrane

Bekesy’s place theory of hearing

Frequency of sound is indicated by the place of organ of Corti that has the highest firing rate

What frequency of music has the highest rate of firing in the base of the organ of Corti?

High

What frequency of music has the highest rate of firing in the apex of the organ of Corti?

Low

Phase Locking

Hairs bend back and forth at particular frequency which corresponds to frequency of sound

Which has a larger range of detecting frequency, phase locking or place coding?

Place coding is effective across entire range of hearing,

phase locking is only effective up to 4,000Hz

Azimuth

Degrees relative to you horizontally

Eg: a sound coming from behind you is at an azimuth of 180°

Are we better at localizing sounds in front of us or to the sides or behind?

We are best at identifying sounds in front of us, much worse on the side and behind

binaural cues for localization

Time difference

Level difference

Interaural time difference

A sound reaches one ear faster than the other

Dominant way of inferring location in humans

Jeffrees neural coincidence model

Interaural Level Difference

Sounds coming from one side will be louder in the corresponding ear

Reduction in intensity occurs mostly for high frequency sounds

What’s better for low frequency sounds? ILD or ITD

ITD is better for low frequency sounds bc no acoustic shadow is made while ILD is better for high frequency sounds

Monaural cues

Cues that only need one ear to work

medial geniculate nucleus

Area in auditory pathway in the thalamus

Core, Belt, and Parabelt

In the cortex

Simple tones active the core

Belt and parabelt respond to more complex stimuli made of many frequencies

What and Where Streams for Sound

What stream handled in temporal lobe

Where stream handled in parietal lobe

Does the visual cortex activate for blind people who use echolocation?

YES

Visual Capture Effect

When the visual source of audio doesn’t match where the sound is actually coming from, we assume it comes from the visual source