intro to speech perception

Question 1

the challenges of speech perception

Answer 1

• Unlike written language, no clear gaps between words
  
  • “the” sounds different in different positions (co-articulation)
  • Accent, gender, and speaking rate
  • Time constraints:
  • We hear up to 200 words per minute
  • Sound is fleeting
  • “Now-or-never bottleneck” (Christiansen and Charter 2016)

Question 2

why study speech perception?

Answer 2

· Primary way in which we communicate
· Need it to help learning to read, as you need to learn the relationship between words and letters with speech
· For people who have a hearing loss

Question 3

what is developmental language disorder

Answer 3

· DLD is a brain difference that makes talking and listening difficult
· DLD affects about 2 children out of every classroom

Question 4

how do we produce speech?

Answer 4

· The lungs push air up the trachea (windpipe)…
· …which vibrates the vocal cords in the larynx (voicebox) -> ‘source’
· Sounds from the vocal cords are then shaped by the supralaryngeal vocal tract -> ‘filter’:
- Pharynx
- Oral cavity (and lips, tongue, teeth)
- Nasal cavity

Question 5

describing speech - consonants

Answer 5

· Consonants are produced with a constriction in the vocal tract
· Classified according to three main features:

Question 6

speech as sound waves

Answer 6

• sound waves: periodic displacement of air molecules, creating increases and decreases in air pressure

Question 7

spectrogram - analysing the frequencies of speech

Answer 7

• A spectrogram is a graph showing how sound amplitude varies as a function of time (x-axis) and frequency (y-axis)
  · Dark grey = large amplitude, light grey = small amplitude
  · Useful because the ear splits sound by frequency so better captures the information available to the brain

Question 8

sourcer-filter theory

Answer 8

Source only:
- source (vocal cords) important for voice pitch and intonation
Source + filter:
- filter (supralaryngeal vocal tract) important for producing different speech sounds (phonemes)
- filtering appears as bands of energy at certain frequencies called ‘formants’
- the lowest three formant frequencies are the most important for speech intelligibility (F1, F2, F3)

Question 9

source-filter theory - vowles

Answer 9

• changing from front to back vowels -> F2 frequency decreases
• changing from high to low vowels -> F1 frequency increases
• so your brain can know which vowel it is hearing by detecting these auditory “cues”

Question 10

source-filter theory - consonants

Answer 10

• second and third formants (F2 and F3) are important cues for identifying consonants

Question 11

how do we perceive phonemes?

Answer 11

1. set up a continuum of sounds between two phonemes
2. run an identification experiment
3. run a discrimination experiment
   · Categorical perception: the tendency to perceive gradual sensory
   · changes in a discrete fashion
   · Three hallmarks of categorical perception:
   
   1. Abrupt change in identification at phoneme boundary
   2. Discrimination peak at phoneme boundary
4. Discrimination predicted from identification (only sound “different” if different phoneme)