Sensation and Perception Final

Physical definition of sound

sound is pressure changes

Perceptual definition of sound

the experience we have when we hear

Frequency

how many times a sound wave repeats (vibrates) each second

Frequency is measured in…

Hertz (Hz)

Sound amplitude

height of peaks in a sound wave (difference between high and low pressures in air)

Sound amplitude is measured in…

decibels

3 perceptual aspects of sound

pitch, loudness, and timbre

Pitch

perceived from frequency (high or low)

Human hearing ranges from…

20-20,000 Hz

Loudness

perceived volume from sound amplitude

Timbre

other perceptual aspects of sound beyond loudness, pitch, and duration (ex. different musical instruments)

2 thresholds for loudness

absolute threshold (minimum) and magnitude estimation

Thresholds depend on…

loudness and frequency

Audibility curve

curve that shows the sound pressure level (SPL), aka the minimum loudness needed to hear different frequencies

Two places frequency is represented in auditory pathway…

The cochlea and auditory cortex (A1)

Frequency in cochlea

different hair cells activate in response different sound frequencies (place theory)

Hair cells near base of cochlea

high frequencies

Hair cells near apex

low frequencies

Frequency in A1

tonotopic map (different parts of A1 respond to different frequencies in organized pattern)

Cochlea

tiny coiled structure in the inner ear that transmits vibration of sound

3 fluid filled canals in cochlea

scala vestibuli, scala media, scala tympani

What do the canals of the cochlea do?

carry waves causing the basilar membrane to move

How does the basilar membrane respond to different sound frequencies?

sound waves travel and reach their strongest point at the spot tuned to that sound’s frequency, making the membrane vibrate

The basilar membrane translates…

frequency of sounds into neural activity for the brain

Organ of corti

structure holding hair cells

Hair cells

detect vibrations and release neurotransmitters that promote auditory signals to the brain for perception

Inner ear

key to both hearing and maintaining equilibrium

Differences in basilar membrane fibers

those at base of cochlea are short and stiff for high frequencies

those at the end are longer and looser for low frequencies

Parts of basilar membrane fibers vibrate…

based on frequency of the sound coming through

Short vs. long basiliar membrane fibers

short fibers → high frequency pressure waves

long fibers → low frequency waves

Transduction of sound begins when…

part of the basilar membrane moves and fibers tickle the organ of corti

Brain detects frequency of sound based on…

location of hair cells being triggered

Cerebral cortex function

interprets electrical signals and plugs them into stored memories to recognize sounds and sources

Steps in auditory pathway

hair cells → auditory nerve → cochlear nucleus → superior olivary complex → inferior colliculus → medial geniculate nucleus (MGN) in thalamus → A1

Auditory location based on…

left vs. right (azimuth coordinates), up vs. down (elevation coordinates), and distance coordinates

Localization of sounds are…

calculated through ITD and ILD

Biaural cues

location cues based on comparison of sound info received by the right and left ears

Interaural timing difference (ITD)

differences in timing of sounds reaching the right ear and left ear

No ITD =

source is equal distance from both ears

ITD =

source is to one side

Interaural level difference (ILD)

difference in sound pressure level reaching the right ear and the left ear (intensity of sound)

ITD is for…

high frequency sounds, decrease intensity of level in further ear

ILD and ITD are not effective for…

elevation judgements

ITD Detectors

neurons that fire when signals reach them from both ears

Brain areas involved in locating sound

A1 and posterior belt area

Two auditory processing pathways

dorsal auditory processing stream and ventral auditory processing stream

Dorsal auditory processing stream

where pathway—toward the parietal lobe

Ventral auditory processing stream

what pathway—temporal lobe

Both processing streams lead to…

the frontal lobe

Evidence methods for auditory processing pathways

Lesion method, neuroimaging, neural recordings

Direct sound

sounds that reach the ear directly

Indirect sounds

sound that reaches the ear after reflecting off of another surface

Problem with direct vs. indirect

both direct and indirect sounds may hit the ear at different timings—-do we hear them as separate sounds?

Precedence effect

when two identical or similar sounds reach the ear within a very short time gap, we perceive the first sound that reaches the ear

When more than one sound is detected…

precedence effect makes us perceive only the first sound

Architectural accoustics

study of how sounds reflect in rooms

Auditory source analysis (ASA)

process where the stimuli made by each source are separated

Two types of grouping

simultaneous and sequential

Simultaneous grouping

situation where sounds are perceptually grouped together since they happen simultaneously in time

Sequential grouping

grouping when sounds come one after another in time

3 cues for simultaneous grouping in ASA

location, onset synchrony, timbre and pitch

Onset synchrony

if the onset is at different times, likely from different sources; if onset at same time, likely grouped together

Timbre and pitch

same timbre and pitches are produced from same source

5 cues for sequential grouping in ASA

Gestalt principle of proximity, similarity of pitch, auditory continuity, experience, auditory stream segregation

Auditory continuity (principle of good continuity)

sounds that stay constant or change smoothly are usually from the same source

Melody schema

representation of a familiar melody in memory (part of experience in ASA)

Auditory Stream Segregation

perception of a string of sounds as belonging together

Acoustic stimulus/signal

pattern of frequencies and intensities of the sound stimulus

Sound produced is based on…

the shape of the vocal tract and articulators

Articulators

tongue, lips, teeth, etc.

Speech sounds are described by (3)

manner of articulation, place of articulation, voice onset time

Manner of articulation

interaction of articulators in speech production

Place of articulation

location of articulators during a speech sound

Voice onset time (VOT)

time delay between when a sound begins and when the vocal chords start vibrating

Phoneme

shorten segment of speech that changes the meaning of a word if changed

Phonemes are the…

basic units of speech (ex. /b/, /a/, /t/)

Acoustic signals are…

variable → sounds can change properties frequently but represent the same thing

There is no simple relationship between a…

phoneme and acoustic signal

2 sources of variability in acoustic signal

context and pronunciation

Forms of context variability

coarticulation and perceptual constancy

Forms of pronunciation variability

between speaker differences and within speaker differences

Coarticulation

overlapping articulation that happens when different phonemes follow each other in speech (ex. /b/ in boot different from /b/ in beat)

Perceptual constancy

we perceive the sound of a phoneme the same despite acoustic signals being different from coarticulation

From pronunciation

changes acoustic signal but not meaning

Between speaker differences

from person to person saying words differently (ex. regional accents)

Within speaker differences

within individual person, talking differently in different contexts (ex. laryngitis losing your voice, baby talk)

Application of variability in pronunciation

differences in IDS and ADS

Infant directed speech (IDS)

“baby talk” with special characteristics that attract an infants’ attention making it easier for the infant to recognize individual words (motherese or parentese)

IDS differs from adult directed speech by being…

slower, higher in and larger range of pitches, more separated and repeated words, positive affect

4 sources for speech perception

acoustic signal, visual info from face/lip movements of others, knowledge of language, experience

Phonemic restoration effect

occurs when listeners perceive a phoneme in a word even though the phoneme is obscured by another sound (ex. white noise, cough)

Forms of knowledge of language

phonemic restoration effect and knowing meaning of words in sentences

Experience in speech perception

speech perception improved with more experience even with distortion or an accent

6 brain areas for language

Broca’s area

Wernicke’s area

Facial area of primary motor cortex

Angular gyrus

Arculate fasciculus

A1 and V1

Broca’s area

speech production

Wernicke’s area

speech comprehension

Angular gyrus

reading and writing

Arculate fasciculus

white matter tract connecting Broca’s and Wernicke’s areas

Lateralization of language function

language localized to the left hemisphere in majority of individuals that are right handed

Left hemisphere is the…

language dominant hemisphere