Is speech special?

Question 1

Source-filter model

Answer 1

• source = larynx

- filter = vocal tract

Question 2

Plotsky et al (2013)

Answer 2

• weak relationship between formants and vocal tract length in humans
• clear relationship in other mammals, but relationship is stronger for oral than pharyngeal component of VT
• radiography of animals and measured relationship between two parts of vocal tract to sound and body size

Question 3

Is a descended larynx special?

Answer 3

• humans start with larynx ascended and descends with age
• after 4 months can choke, but before cannot
  1. larynx is sexually dimorphic (the differences in appearance between males and females of the same species, such as in colour, shape, size, and structure, that are caused by the inheritance of one or the other sexual pattern in the genetic material)
  2. we lost laryngeal air sac
  3. larynx has descended
• we do not have air sacs
• some animals have a descended larynx too e.g. dogs do - evolutionary adaptations that allow us to speak - dogs larynx goes down temporarily to increase loudness and give a more attractive sound
• but human lowering is permanent - might be an adaption of speech

Question 4

Hypothesis for permanently lowered larynx

Answer 4

1. phonetic expansion hypothesis due to adaption to allow for mouth breathing - both other animals also mouth breath
2. laryngeal lowering was non-adaptive by-product of walking upright (but other animals e.g. kangaroos walk upright and do not have a lowered larynx)
3. size exaggeration hypothesis

A descended larynx:

• doesn’t appear to be all that special
• gives a permanent signal of size exaggeration - sound larger then they are
• not evolved specifically for better vocal control - may even go against in some cases
• allows for more freedom of movement and production of a wider range of formant patterns

Question 5

Dunn et al (2015)

Answer 5

• trade off between vocal tract and testes size in howler monkeys ]- large hyoids and small testes
• therefore, high levels of vocality mediated competition - increase acoustic perception of body size

Question 6

Is speech perception special?

Answer 6

• hearing is not special
• Kuhl and Miller - chipmunks can distinguish sounds for rewards
• humans can distinguish minimal pairs
• language specific

Question 7

Lieberman (1957)

Answer 7

• idea that perception system imposes categories
• categorical perception (CP) originally found for VOT
• listeners showed sharp identification between categories relevant for their language
• listeners show good discrimination of stimulus pairs that straddle category boundaries
• listeners show poor discrimination of stimulus pairs from the same category (Kuhl)
• also can discriminate between faces etc.