Topic 6 - Speech Perception

Question 1

Acoustic Signal

Answer 1

Produced by air that is pushed up from the lungs through the vocal cords and into the vocal tract

Question 2

Vowels

Answer 2

Vowels are produced by vibration of the vocal cords and changes in the shape of the vocal tract by moving the articulators

These changes in shape cause changes in the resonant frequency of the vocal tract and produce peaks in pressure at a number of frequencies called formants

Each vowel has a characteristic series of ‘formants’ (resonant frequencies)

Question 3

Articulators

Answer 3

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

Question 4

Formants

Answer 4

Resonant Frequencies

The first formant has the lowest frequency, the second has the next highest, etc.

Question 5

Sound/Speech spectrograms

Answer 5

Sound/Speech spectrograms are a better way to show the changes in frequency and intensity for speech

Question 6

Consonants

Answer 6

Produced by a constriction of the vocal tract and air flow around articulators

Question 7

Phoneme

Answer 7

smallest unit of speech that changes meaning of a word

In English there are 47 phonemes - 13 major vowel sounds and 24 major consonant sounds

Question 8

Variability problem

Answer 8

There is no simple correspondence between the acoustic signal and individual phonemes

• Variability comes from a phoneme’s context
• Acoustic signals that vary can be perceived categorically (/b/ as in ‘bat’ or ‘bite’) i.e., as ‘the same’ sound

Question 9

Coarticulation

Answer 9

overlap between articulation of neighbouring phonemes also causes variation

Question 10

Variability between different speakers

Answer 10

Speakers differ in pitch, accent, speed in speaking, and pronunciation

• This acoustic signal must be transformed into familiar words
• People perceive speech easily in spite of the variability problems due to perceptual constancy

Question 11

Categorical perception

Answer 11

This occurs when a wide range of acoustic cues results in the perception of a limited number of sound categories

Question 12

Voice onset time (VOT)

Answer 12

time delay between when a sound starts and when voicing begins (vocal chords begin to vibrate)

Question 13

VOT experiment Eimas & Corbit

Answer 13

VOT for /da/ is 17ms (short) and /ta/ is 91ms (long)

Computers were used to create stimuli with a range of VOTs from long to short

Listeners do not hear the incremental changes, instead they hear a sudden change from /da/ to /ta/ at the phonetic boundary

Thus, we experience perceptual constancy for the phonemes within a given range of VOT

Question 14

The McGurk Effect

Answer 14

Visual stimulus shows a speaker saying “ga-ga.”

Auditory stimulus has a speaker saying “ba-ba.”

Observer watching and listening hears “da-da”, which is the midpoint between “ga” and “ba.”

Observer with eyes closed will hear “ba.”

Question 15

Physiological link between vision and speech

Answer 15

Calvert et al. showed that the same brain areas are activated for lip reading and speech perception.

Question 16

FFA activation

Answer 16

Von Kreigstein et al. showed that the FFA is activated when listeners hear familiar voices

This shows a link between perceiving faces and voices.

Question 17

Experiment by Rubin et al.

meaning and phoneme

Answer 17

Short words (sin, bat, and leg) and short nonwords (jum, baf, and teg) were presented to listeners.

The task was to press a button as quickly as possible when they heard a target phoneme

On average, listeners were faster with words (580 ms) than non-words (631 ms)

Question 18

Experiment by Warren

meaning and phoneme

Answer 18

Listeners heard a sentence that had a phoneme covered by a cough

The task was to state where in the sentence the cough occurred.

Listeners could not correctly identify the position and they also did not notice that a phoneme was missing - called the phonemic restoration effect

This did not happen for non-word sentences

Question 19

Experiment by Miller and Isard

meaning and phoneme

Answer 19

Stimuli were three types of sentences:

- Normal grammatical sentences 
- Anomalous sentences (made no sense) that were grammatical
- Ungrammatical strings of words

Listeners were to shadow (repeat aloud) the sentences as they heard them through headphones

Results showed that listeners were – 89% accurate with normal sentences – 79% accurate for anomalous sentences – 56% accurate for ungrammatical word strings

Question 20

Segmentation Problem

Answer 20

there are no physical breaks in the continuous acoustic signal

Top-down processing, including knowledge a listener has about a language, affects perception of the incoming speech stimulus

Segmentation is affected by context, meaning, and our knowledge of word structure

Question 21

Speech Segmentation

Answer 21

the perception of individual words in a conversation

Question 22

Word Structure, Segmentation

Answer 22

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

Question 23

Statistical Learning experiment by Saffran et al.

Answer 23

Learning phase - infants heard nonsense words in two-minute strings of continuous sound that contained transitional probabilities

Nonsense words were in random order within the string

If infants use transitional probabilities, they should recognize the words as units even though the string of words had no breaks

Question 24

Indexical characteristics

Answer 24

characteristics of the speaker’s voice such as age, gender, emotional state, level of seriousness, etc

Question 25

Speaker characteristics experiment by Palmeri et al.

Answer 25

Listeners were to indicate when a word was new in a sequence of words.

Results showed that they were much faster if the same speaker was used for all the words, than when a different speaker was used for each

Question 26

Broca’s aphasia

Answer 26

Individuals have damage in Broca’s area in frontal lobe

Laboured and stilted speech and short sentences but they understand others

Question 27

Wernicke’s aphasia

Answer 27

individuals have damage in Wernicke’s area in temporal lobe

Speak fluently but the content is disorganized and not meaningful

They also have difficulty understanding others and word deafness may occur in extreme cases

Question 28

Brain damage

Answer 28

Some patients with brain damage can discriminate words but are unable to discriminate syllables (and vice versa)

Question 29

Brain scans found:

Answer 29

A “voice area” in the STS that is activated more by voices than other sounds

A ventral stream for recognizing speech and a dorsal stream that links the acoustic signal to movements for producing speech - called the dual stream model of speech perception

Question 30

Experience dependent plasticity

Answer 30

Before age one, human infants can tell difference between sounds that create all languages

The brain becomes “tuned” to respond best to speech sounds that are in the environment

Other sound differentiation disappears when there is no reinforcement from the environment