PSYC 3220 Hearing & Auditory Perception

Cochlea

Tiny, coiled structure in the inner ear, filled with fluid. Responsible for turning sound into signals your brain can understand

Hair cells

Tiny sensory cells inside of the cochlea, with little hair-like projections (stereocilia)

Bend when sound vibrations move through the cochlea, are the actual receptors for sound

Hair cells transduction

Convert sound waves (mechanical energy) → electrical signals (neural signals)

Hair cells role in hearing

Detect the vibrations, transduction allows for brain to interpret sound

Physical definition of sound

Sound is pressure changes

Perceptual definition of sound

The experience we have when we hear

Frequency

Number of cycles/second (physical)

Hertz

How we measure frequency

Sound amplitude

The height of the peaks in the wave

Decibel

How we measure sound amplitude

Perceptual aspects of sound

Pitch, loudness, timbre

Pitch

A tone's experienced highness or lowness; depends on frequency (perceptive)

Loudness

A sound's intensity perceived from sound amplitude

Timbre

Other perceptual aspects of sound beyond loudness, pitch, and duration

EX) Different musical instruments

Threshold for loudness

Absolute threshold, Magnitude estimation

Depend on loudness and frequencies

Thresholds

Audibility curve

Curve that shows the sound pressure level (SPL) at threshold for frequencies across the audible spectrum

Frequency in cochlea

Which hair cells are activated corresponds to frequency of sound (place theory)

Hair cells near base

High frequencies (pitch)

Hair cells near apex

Low frequencies (pitch)

Hair cells → auditory nerve → cochlear nucleus → superior olivary complex → inferior colliculus→ MGN → A1

Steps in primary auditory pathway

Receptor of auditory pathway

Hair cells

Thalamic nucleus of auditory pathway

MGN (medial geniculate nucleus)

Primary receiving area of auditory pathway

A1 (primary auditory cortex)

Binaural cues

Location cues based on comparison of sound info received by the right ear and the left ear

ITD, ILD

Binaural cues

Interuaral timing difference (ITD)

Difference in timing sounds reach the right ear and the left ear

No ITD

Source is equal distance from both ears

EX) Sound right in front of you, both ears receive sound at same time

ITD

Source is to one side

EX) Sound from right side of room, right ear will receive sound before left ear

Interaural level difference (ILD)

Difference in sound pressure level reaching the right and left ear

For high frequency sounds

Decrease intensity in further ear

A1, Posterior belt area

Brain areas involved in locating sound

ITD detectors

Neurons that fire when signals reach them from both ears

Dorsal auditory processing stream

Where is the sound coming from?

Leaving A1, heading towards the parietal lobe

Dorsal auditory processing stream

Ventral auditory processing stream

What exactly did i hear?

Temporal Lobe

Ventral auditory processing stream

Lesion method, Neuroimaging , Neural recordings

Evidence for 2 auditory processing pathways

Direct sound

Sound reaches ear directly

EX) someone directly talking to you in a quiet room

Indirect sound

Sound that reaches ear after reflecting off of another surface

EX) sound echos off of halls when someone speaks

Precedence effect

When two identical or similar sounds reach the ear with a very short time gap, the listener perceives the first sounds that reaches the ear

Architechtual acoustics

Study of how sounds reflect in rooms

Auditory Scene analysis (ASA)

Process where the stimuli made by each source are separated; How your brain figures out what sounds belong together and what comes from different sources.

Simultaneous grouping

When sounds are perceptually grouped together since they happen simultaneously in time

Example of Simultaneous grouping

Grouping trumpets together in an orchestra; playing at the same time

Sequential grouping

Grouping when sounds come one after another in time

Example of Sequential grouping

Car alarm, beeps multiple times in a row; know it's one car and not multiple at once

Onset Synchrony

Onset synchrony is when different sounds start at the same time, and your brain groups them together as coming from the same source.

Example of Onset Synchrony

In a band, when a drum and guitar hit at the exact same moment, your brain groups them together as part of the same musical event.

Location, Onset Synchrony, Timbre & pitch

Cues for simultaneous grouping in ASA

Similarity in pitch, Gestalt principle of proximity, Auditory Continuity, Experience, Auditory Stream segregation

Cues for sequential grouping in ASA

Auditory Continuity (Principle of good continuity)

Sounds that stay constant or change smoothly are perceived as coming from the same source.

Example of auditory continuity

Imagine you hear a siren from an ambulance.

The pitch smoothly goes up and down as it passes by.

Even though the sound is changing, your brain hears it as one continuous sound from the same ambulance, not different sources.

Melody Schema

Representation of a familiar melody in memory (twinkle twinkle little star)

Auditory Stream Segregation

When your brain separates sounds into different streams because they are too different (in pitch, timing, or location) to be grouped together.

Auditory Stream Segregation Example

Imagine you’re listening to two instruments, like a flute and a drum.

They sound very different, so your brain separates them into two distinct streams, instead of hearing them as one combined sound.