PSY 400 Final

What does the Organ of Corti do?

Transduces sound in neural signals

When is interaural level difference cue effective

At higher frequencies

Indirect sound

Sound that reaches the ears after bouncing off a wall or a floor

What kind of organization do cells in the primary auditory cortex show

Tonotopic organization

Where do we typically find neurons specifically designed to detect interaural time differences

Superior Olivary Nucleus

Using fMRI Belin et al. were able to reveal that in humans the STS is

Activated more for human voices than other sounds

What is the function of the anterior belt area

Perceiving complex sounds and patterns of sound

What do the muscles in the middle ear aim to do?

Dampen the ossicles’ vibrations at high intensities.

Davis and others tested subjects to determine their ability to perceive degraded speech and found that

Higher level information can help in understanding degraded speech

What is the shortest segment of speech that, if changed, changes the meaning of the word?

Phoneme

What is categorical perception

Ability to collapse a wide variety of acoustic signals into limited bins

Presbycusis

Hearing loss that occurs as a function of age

What auditory localization dimension extends along the vertical plabe

Elevation

What is NOT a heuristic that we typically use to perceptually organize auditory stimuli

The rhythm of 2 sounds

What does damage to Broca’s area result in?

Slow, labored speech

What unit do we measure frequency in?

Hertz (Hz)

A guinea pig tonotopic map shows that a receptor close to the apex will respond to a tone of…

60 Hz

If a person has temporal damage that affects their ability to recognize sound, what does this provide evidence for?

What and where pathways in audition

Kat wants to buy a dog whistle that her dog can hear, but she cannot. What freq. range should the whistle fall into?

30,000 to 40,000 Hz

What is a formant?

Frequency bands with higher amplitudes among the harmonics of a vowel sound

A. Pinna

B. Malleus

C. Incus

D. Stapes

E. Auditory Nerve

F. Cochlea

G. Auditory Canal

H. Tympanic membrane (eardrum

Pure Tones

Created by a sine wave and rarely found in nature

Sound Wave

Cycles of alternating high and low pressure regions traveling through a medium.

Amplitude (intensity)

Difference in pressure between high/low peaks

Frequency

1 Hz = 1 cycle/second

Tone heigh is the increase in pitch that happens when frequency is increased

Loudness (dB)

Perceptual quality most closely related to the level or amplitude of an auditory stimulus.

Pitch

Low frequency perceived as lower sound; Higher frequency perceived as higher pitch.

Human Hearing Range

0 - 140 dB (140 is normal pain threshold)

20 - 20,000 Hz, Most sensitive to 2000 - 4000 Hz

Timbre

Created partially by the multiple frequencies that made up complex tones. Attach, deacy, vibrato, tremolo also contribute.

Harmonics

Periodic complex tones consisting of several pure tones

Fundamental Frequency

The first harmonic and its repetition rate.

Outer Ear

Pinna - helps with sound localization

Auditory Canal - Tube-like 3cm long structure. Protects the tympanic membrane at the end of the canal. Resonant frequency of the canal amplifies frequencies between 1000 & 5000 Hz

Middle Ear

2 cubic cm cavity separating inner ear from the outer ear. Contains the ear drum and 3 ossicles.

Malleus moves due to vibration of tympanic membrane

Incus transmits vibrations of malleus

Stapes transmits vibrations of incus to the inner ear via the oval window of the cochlea; The oval window amplifies the sound.

Also has 2 muscles that can limit ossicle movement when sounds are very loud.

Why are ossicles needed?

Inner ear is filled with fluid and pressure changes transmit poorly through this fluid. Ossicles amplify the vibration for better transmission

Acoustic Reflex

Middle ear muscles dampen the ossicles’ vibrations to protect the inner ear from potentially damaging stimuli.

Inner Ear

Contains the cochlea, a fluid filled snail like structure (35 mm long) set into vibration by the stapes. Divided into the vestibular canal and the tympanic canal by the cochlear partition

Cochlear partition extends from the base to the apex.

Also contains the Organ of Corti and the Round window (lets excess pressure escape the cochlea)

Organ of Corti

Basilar Membrane vibrates in response to sound and supports the organ of corti

Inner and outer hair cells are receptors for hearing

Tectorial membrane extends over hair cells.

Transduction at the hair cells takes place due to interaction of these structures. Cilia bend in response to movement of organ of corti and tectorial membrane. Movement in one direction opens ion channels, movement on other direction closes them. This causes a burst of electrical signals

Basilar Membrane

Higher frequencies at the base, lower frequencies at the apex

Place Theory of Hearing

Frequency of sound is indicated by the place on the Organ of Corti that has the highest firing rate. Envelope of the traveling wave indicates the point of maximal displacement of the basilar membrane. Hair cells at this point are stimulated most strongly leading to strong nerve firing at this location. Position of the peak is a function of frequency.

Tonotopic map

Cochlea shows orderly map of frequency along its length. Apex responds best to low frequencies, while the base responds best to high frequencies.

SONIC MG

SON = superior olivary nucleus

IC = inferior colliculus

MG = medial geniculate nucleus

Pathway to the Brain

SONIC MG

Core area

Belt area

Parabelt area

Core area

Area of the auditory cortex consisting of the primary auditory cortex, the rostral core, and the rostro-temporal core

Belt area

A region of the auditory cortex that wraps around the auditory core regions.

Anterior is involved in perceiving complex sounds and patterns of sound

Posterior is involved in localizing sounds

Parabelt area

A region of the auditory cortex, in addition to the belt area, that wraps around the auditory core regions.

Presbycusis

Hearing loss due to age. Greatest loss at high frequencies, affects males more severely, and appears to be caused by exposure to damaging noises or drugs

Noise-induced hearing loss

Loud noise can severely damage Organ of Corti. OSHA standards for noise levels at work are set to protect workers. Leisure noise can also cause loss.

Auditory Space

Surrounds an observer and exists whether there is sound

Azimuth

left and right horizontal plane in auditory space

Elevation

Up and down vertical plane in the auditory space

Interaural Level Difference (ILD)

Difference in sound pressure level reaching the 2 ears. Reduction in intensity occurs for high frequency sounds for the far ear due to acoustic shadow. Good at frequencies above 1000 Hz, not so good below.

Interaural Time Difference (ITD)

Difference between the times that sounds reach the 2 ears. When distance to each ear is the same, no difference in time, but when the source is to the side of the observer, times will differ. People can discriminate differences as small as 10 to 20 millionth of a second. Works best for lower frequencies.

Cone of Confusion

Neither ITD or ILD are helpful for elevation. For any given ITD or ILD there is a number of spatial locations that could generate differences

Pinna’s Role in Sound Localization

Sound bounces around the folds of the pinna differently depending on the location of the sound. Each location has a unique spectral signature. Useful for vertical locations. Can also amplify sounds.

What Auditory Pathway

Ventral stream starts in the anterior portion of the core and belt and extends to the prefrontal cortex - used to identify sounds

Where Auditory Pathways

Starts in the posterior core and belt and extends to the parietal and prefrontal cortices and used to locate sounds

Direct sound

Sound that reaches the listener’s ears straight from the source.

Indirect sound

Sound that is reflected off of environmental surfaces and then to the listener

Reverberation Time

The time it takes sound to decrease by 1/1000th of its original pressure. If too long, sounds are muddled. If too short, sounds are dead. Ideal time is 2 seconds.

Heuristics to organize environmental auditory stimuli

Onset time - sounds that start at different times are likely to come from different sources

Location - a single sound source tends to come from 1 location

Similarity of timbre and pitch - similar sounds are grouped together

Proximity in time - sounds that occur in rapid succession usually come from the same source

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

Melody Schema

a representation of a familiar melody that is stored in a person’s memory

Vowels

Made with unrestricted airflow

Consonants

Made with restricted airflow

Formants

Frequency bands with higher amplitudes among the harmonics of a vowel sound; each individual vowel sound has a specific pattern of these.

Formant Transitions

Rapid changes in frequency preceding or following consonants

Place of Articulation

The point along the vocal tract at which the airflow is constricted.

Manner of Articulation

How airflow restriction in the vocal tract occurs

Voicing

Whether the vocal cords are vibrating or not

Voiced Consonant

Consonants that are produced using the vocal cords

Unvoiced consonants

Consonants that are produced without using the vocal cords

Spectrogram

indicates the pattern of frequencies and intensities over time that make up the acoustic signal. Frequency is indicated on the vertical axis and time on the horizontal axis; intensity is indicated by darkness, with darker areas indicating greater intensity. The horizontal bands are formants

Phoneme

The smallest unit of speech that changes the meaning of a word. 47 in English. The sounds that are used to create words in a specific language

Variability Problem

There is no simple correspondence between the acoustic signal and individual phonemes. Variability comes from a phoneme’s context. People perceive speech easily despite this due to perceptual constancy.

Coarticulation

Overlap between articulation of neighboring phonemes also causes variation.

Perceptual Constancy

The fact that we perceive the sound of a phoneme as the same even though the acoustic signal is changed by coarticulation

Categorical Perception

Occurs when a wide range of acoustic cues results in the perception of a limited number of sound categories.

Use experiments on voice onset time (VOT) to test, time delay between that a sound starts and voicing begins. We experience perceptual constancy for phonemes within a given range of VOT.

McGurk Effect

What we see affects what we hear. Visual stimulus shows “fa”, auditory stimulus says “ba”. Observer hears “fa” when eyes are open but “ba” when closed.

Phonemic Restoration Effect

An illusion in which participants hear sounds that are masked by white noise, but context masks the missing apparent sound.

The segmentation problem

There are no physical breaks in the continuous acoustic signal.

Speech Segmentation

Affected by context, meaning, and our knowledge of word structure.

Transitional probabilities: the chance that one sound will follow another in a language.

Statistical learning: the process of learning transitional probabilities and other language characteristics. Infants as young as 8 months show statistical learning.

Davis et al. on Degraded Speech

Made participants listen to a vocoded sentence and had them write down what they could hear. Did this for 30 sentences. Performance improved as they listened to more sentences.

In different experiment, gave participants a degraded sentence, then a clear version of that sentence, then the degraded version again. Participants reported hearing words in the second degraded version they didn’t hear in the first. Called the pop-out effect; higher level info is important to speech perception.

Broca’s aphasia

Labored and stilted speech and short sentence but they understand others. Individuals have damage in Broca’s area in frontal lobe.

Wernicke’s aphasia

Speak fluently but the content is disorganized and not meaningful. Also have difficulty understanding others, and word deafness may occur in extreme case. Individuals have damage in wernicke’s area in temporal lobe

Belin et al. on STS

Used fMRI to locate a voice area in the superior temporal sulcus. The voice area is activated more by voices than other sounds.

Dual Stream Model of Speech Perception

A ventral stream for recognizing speech and a dorsal stream that links the acoustic signal to movements for producing speech.

Articulators

Includes structures such as the tongue, lips, teeth, jaw, and soft palate