Week 10 pt.1 : Speech perception

Question 1

Vocal tract path

Answer 1

1. Trachea = air that produces the sound passes through the trachea (or windpipe)
2. Larynx = next into the larynx (voice box)… vocal folds within larynx open & close to change pitch of the sound… however, parts of the vocal tract higher up are necessary for consonant sounds
3. Pharynx = next into pharynx
4. Uvula = closing the uvula prevents sounds from going up through the nasal cavity, affecting the quality of sound
5. Mouth and nose… Where teeth, tongue, lips & uvula can affect the sound signal

Question 2

speech is…

Answer 2

very complex & variable over time… many different moving parts come together to produce the intricacies of this signal… the air is provided through exhalation from the lungs

Question 3

air passage…

Answer 3

• changes in density of air are caused by vibrations of the vocal folds/cords
• vocal folds… lay horizontally along the larynx & vibrate between an open & closed position to produce sound (rate at which they vibrate determines pitch)
• air them goes through spaces & articulators… they function together to shape sound wave (oral cavity, soft palate, tongue, lips & teeth)

Question 4

Cocktail party effect

Answer 4

• listening to speech of one person but attention is distracted by hearing someone say your name from across the room
• this suggests that our attentional mechanism does not screen out all perceptual inputs even when we are focused on one conversation

Question 5

vowels

Answer 5

• produced by unrestricted airflow from through the pharynx and the mouth & by vibrations of the vocal cords
• changing the shape of the mouth makes different vowel sounds
• each vowel sound has a characteristic pattern of harmonics…

Question 6

in vowels, the harmonics that are the highest amplitude are known as…

Answer 6

• formants (peaks in the sound distributions)
• formants are the frequency bands with higher amplitudes among the harmonics of a vowel sound
• each vowel sound has a specific pattern of formants
• fundamental frequency is the same for each vowel & only distinguishable by formant frequencies

Question 7

What can you do with the location of the first and second vowel formants?

Answer 7

• scientists can plot a talkers vowel space using the 2 vowel formants across speech sounds
• the axes are these 2 formant frequencies and each circle shows the bounds of a given vowel sound
• there is very little overlap between the representations & this highlights articulatory systems ability to function very will

Question 8

Consonants

Answer 8

• produced by restricting the airflow in one place or another along the way up from the larynx

Question 9

3 physical features important in determining the sound of a consonant…

Answer 9

1. place of articulation… the point along the vocal tract at which air is constricted (e.g. tongue, lips teeth, hard/soft palette)
2. manner of articulation… how the restriction occurred (e.g. lips pushed together/tongue at front/back of mouth etc.)
3. voicing… whether the vocal cords are vibrating or not (‘b’ voiced consonant & ‘p’ unvoiced consonant)

Question 10

mouth shape & consonant sound…

Answer 10

• p/b sound = passage of air stopped briefly via soft palate & press lips together then let out a burst of air
• t/d sound = air stopped briefly by putting tongue against alveolar ridge behind teeth
• f/v sound = produced by placing upper teeth against lower lip
• k/g sound = air topped by pressing back of tongue up against soft palate

Question 11

Voicing onset time

Answer 11

• within a subset of consonants like t/d… the manner of articulation are the same for both
• so, to distinguish we add an additional cue - voicing onset timing
• the time at which the syllable transitions from the consonant sound to the vowel sound in a sound like ‘ta’ or ‘da’ (‘ta’ later cuz t is not a voiced consonant)

Question 12

Phonemes

Answer 12

• basic units of sound in human language
• International Phonetic Alphabet - all phonemes used in human language
• English has 15 vowel sounds and 24 consonant sounds

Question 13

Coarticulation

Answer 13

• the shape of the vocal tract when producing a specific consonant differs depending on what sound is going to follow it (‘ba’ vs ‘bo’)
• this is coarticulation
• the frequency content of syllables change as a function of the vowel sound in sound spectrograms
• we can feel these differences in our mouths & tongues when we say them
• as perceivers we do not hear the differences in the sounds & this is an example of auditory constancy

Question 14

Categorial perception

Answer 14

• refers to our perception of different acoustic stimuli as being identical syllables up to a point at which our perception suddenly shifts to perceive another
• we do not hear variation in the sound, we only hear one phoneme then the other
• Categorial perception translates a wide range of voicing into one phoneme

Question 15

Word boundaries

Answer 15

• one of the biggest challenges to speech perception & language learning is determining word boundaries in speech
• within a stream of speech, definitive word boundaries do not exist
• it may be very clear to us where boundaries belong but only in our own language and has little to do with the actual physical parameters of the speech sound itself
• top-down word segmentation

Question 16

how are the word boundaries learned?

Answer 16

• thru exposure & attention to environment
• much learning happens very early in life
• motherese may support language learning… adults emphasize frequency contours & word boundaries when speaking to infants which might help them learn it

Question 17

discerning word boundaries

Answer 17

• syllable transitions occurring within words are encountered more often than those that occur between words through everyday language
• learning theories suggest we are able to pick up on these differences in regulatory & learn that low likelihood transition points likely compromise the boundaries between words

Question 18

Phonemic restoration effect

Answer 18

• top-down processing of what one expects to hear overrides input from the cochlea
• very strong subjective effect
• context clearly indicating a blank word in a sentence but the person actually hears the word being said even tho its not
• works even when the context of the missing sound occurs after the missing sound… so much occur at a pre attention stage in speech perception processing
• areas in the auditory cortex involved & prefrontal lobe

Question 19

General mechanism theories of speech perception

Answer 19

• speech no different than any other sound & we use same mechanisms
• only thing that makes speech important is its importance which is learned

Question 20

Special-mechanism theories of speech perception

Answer 20

• because of the importance of language to humans, special mechanisms have evolved that are specific to speech & not used in other sound processing
• evidence comes from mcgurk effect e.g.

Question 21

development of phoneme perception

Answer 21

• babies have ability to understand all phonemes and language
• by the time they are 10 months old they started showing perceptual narrowing… regularly experienced phonemes are honed in on & simultaneously diminish ability to discriminate unfamiliar phonemes

Question 22

audio-visual speech benefits

Answer 22

• our perception of speech is dramatically affected by the combination of auditory & visual speech cues
• auditory & visual cues combine in our brains to generate the best estimate possible of our environment
• articulators make different movements to make different sounds & this provides useful info when trying to disambiguate unclear signals (e.g. speech in noisy room)
• there is a lot of ambiguity when we only have sound info

Question 23

McGurk…

Answer 23

• clearest example of how visual cues influence the perception of speech comes from an experiment reported by McDonald & McGurk
• video of someone saying sounds like ‘ba’, ‘da’ and ‘the’ but the audio doesn’t always match what the speakers mouth is acc saying
• but participants perceive the sounds as being different from what they acc hear and what phoneme the mouth makes the they’re watching

Question 24

speech in the brain…

Answer 24

• largely isolated to left hemisphere
• broca’s area, wernicke’s area & angular gyrus

Question 25

Broca’s area

Answer 25

• ‘what’ pathway
• this region was believed to integrate info from the auditory & pro-motor cortices in order to direct speech perception
• Broca’s aphasia = nonfluent speech

Question 26

Wernicke’s area

Answer 26

• thought to be the dominant brain region involves in speech perception
• wenicke’s aphasia = absence of understanding language

Question 27

Angular gyrus

Answer 27

• plays a role in complex language perception including, the successful interpretation of written language

Question 28

Aphasia…

Answer 28

impairment in language production or comprehension brought about by neurological damage

Question 29

Speech in the brain in 2023

Answer 29

• the speech network is much larger than the 3 subsections
• there is several regions involved in interpretation & production of articulatory movement (dorsal ‘where’)
• also several regions in the temporal lobe that range from basic sound perception to high level conceptual understanding (ventral ‘what’)
• still mainly in left hemisphere

Question 30

Temporal voice area

Answer 30

• one area present in both hemispheres is the temporal voice area
• sensitive to voice sounds (alike FFA in vision)

Question 31

recreating sounds from brain activity

Answer 31

• in an experiment, researchers showed they can reproduce something that sounds almost like speech from recordings of the neural activity within the temporal voice area
• this is evidence that the brain is encoding speech sounds here

Question 32

Perceiving your own voice

Answer 32

• our hearing mechanisms are so sensitive to deviations from the norm
• participants are quickly able to adapt their speech output and reshape articulators so that what they hear more closely resembles the words they intended to produce when listening to themselves
• Our auditory system is very finely tuned to differences from the expected sound input
• Strong connections between the auditory system and the centers that control motor articulators allow us to very rapidly correct for any difference between the sounds we meant to produce and the ones we ultimately perceived
• This process appears to be critical to language learning across species (same motor loop involved in learning of songs across species of songbird)