Two critical areas of change as we diverged from our evolutionary relatives: 1. Changes to peripheral mechanisms

Transcription

1 Two critical areas of change as we diverged from our evolutionary relatives: 1. Changes to peripheral mechanisms 2. Changes to central neural mechanisms Chimpanzee vs. Adult Human vocal tracts 1

2 Human Infant vs Chimpanzee vocal tracts Crelin ES. Development of the Upper Respiratory System, Clinical Symposia, Vol. 28, No. 3, 1976 Faucium channel View looking into the mouth to illustrate the interlocking of the soft palate and epiglottis. 13 Source: Brian Palmer, DDS (2001) 2

3 60,000 year-old hyoid bone from Neanderthal largely indistinguishable from contemporary human hyoid Source: Plos One Figure 1. Male Homo sapiens and Pan troglodytes hyoid bones. HUMAN-CHIMP COMPARISON: VERY DIFFERENT D Anastasio R, Wroe S, Tuniz C, Mancini L, Cesana DT, et al. (2013) Micro-Biomechanics of the Kebara 2 Hyoid and Its Implications for Speech in Neanderthals. PLOS ONE 8(12): e doi: /journal.pone

4 LING 290 Computer Imaging of Hyoids Homo neanderthalensis Homo sapiens Source: Plos One Source-Filter Theory of Speech Production 4

5 SOURCE: The larynx produces a complex sound The sound of voicing consists of the following: F0: fundamental frequency ( Hz for adult males, Hz for adult females) a rich array of components at other frequencies called harmonics e.g., 200, 300, 400, 500 Hz... FILTER: SLVT modifies (filters) the source sound It allows some frequencies (harmonics) to pass through and it suppresses other frequencies The frequencies that pass through form bands of energy called FORMANTS 5

6 Waveform and spectrogram showing /i/, /ɑ/, /u/. FILTER: The SLVT acts as a filter It allows some frequencies (harmonics) to pass through and it suppresses other frequencies The frequencies that pass through form bands of energy called FORMANTS F1 = formant #1 (lowest) F2 = formant #2 (higher) F3 = formant #3 (still higher) and more... Formant = a band of harmonics in a particular frequency region. 6

7 Formants are the result of resonance Resonance = the tendency of things to oscillate in response to a sound Source Filter Theory in Action: Artificial Larynx (Vocal Prosthesis) Demo of Electrolarynx 7

8 Fun with the Source Filter Theory Sonovox Homo sapiens: Summary of peripheral mechanisms Good control over breathing. Small, well-innervated tongue. Two-tube vocal tract allows formant patterns Oral cavity Pharyngeal cavity Human hearing is very good in the Hz range (very important information in speech --- formants!) 8

9 Other members of homo: Peripheral mechanisms Fitch: we cannot say much for sure soft tissue doesn t fossilize can only guess about extinct human larynges and SLVTs. Why did homo sapiens evolve in this way? 9

10 Two competing views: The changes in homo that make speech (and language) possible evolved as an innate language capacity (in-born language abilities) that persisted because of its survival value OR --- because of factors largely unrelated to language (we happen to exploit central and peripheral structures when we speak) Unusual vocal adaptations A. hammerhead bat: huge larynx B. howler monkey: huge larynx and hyoid C. male red deer: very low larynx, which can be lowered even more D. humans: low larynx E. duckbill dinosaur: huge nasal cavity extending into crest of skull Source: WT Fitch 10

11 long SLVT lower resonances longer vocal folds lower F0 Benefits of anything else that makes you sound big sounds scarier an advantage in defense sounds healthier and more robust sexual attractiveness Homo sapiens: Central mechanisms Good Mimetic Ability Mimetic ability: humans are extremely good imitators must be tied to something in our brains, but when did this ability arise? 11

12 Central mechanisms (Fitch) Good mimetic ability occurs in oscines (songbirds) benefits for mating males with many songs more attractive benefits for defense many songs sounds like many different birds ( Beau Geste effect) Central mechanisms (Fitch) Good mimetic ability occurs in oscines (songbirds) is rare in mammals observed in seals, cetaceans, modern humans other primates? not so much! 12

13 Central mechanisms (Fitch) 2 nd benefit of good mimetic ability in oscines, killer whales, humans... è seems to facilitate markers of group membership (shibboleth, for identifying friends and enemies) markers of individual identity (cetaceans recognize individuals!) Good Mimetic Ability Another example of parallel evolution birds have it cetaceans have it homo sapiens have it but it arose in different ways at different times 13

14 Good Mimetic Ability other extant primates don t have it homo neanderthalensis? unknown, but possible other homo? unknown Human vs Primate Brain Comparisons Human brains develop differently from gestation onward 14

15 Brain size (cranial capacity in cc) measured from endocasts of braincases Postnatal Chimp Prenatal Chimp Source: Smithsonian Human Origins Brain size (cc), Human Humans: Brain growth continues much longer Rapid even after birth Source: Smithsonian Human Origins 15