BOUCHARD Kristofer UCSF SPEECH Cortical Control 25 Feb 2013

(before this talk I chat with two resch from ShenoyLab  (motor control:
Sergey  Stavisky and  Dan O'Shea:
Sergey says that  info content of  cortical signals for reaching is well understood (really?)
(angle, velocity, position all meshed together)

post doc  UCSF  in Edward Chang's lab...

did grad work  at UCSF in songbird  learning of songs...  

now with humans... ecog data... prod of speech   func organization of speech...

the cortical control of human speech articulation...

language is defining. human characteristic...

6 to 8 M americans have language impairment...   stuttering, spasticity...

has spurred development of speech prostheses  eg  steven hawking...

penfield and roberts 1959...

he shows clip :  speech pre-motor and motor   with stim...

anatomical hierarchy

broca,  SMA and pre=motor  projects to sensory  and motor cortex  and then to vocal tract...

1) what is organization of articulator representations...

lips,  jaw, tongue, larynx  are   topograph mapped...
 but when stim those areas in M1  just get  spasticity... no speech...

guenon is  U shape  at bottom of central sulcus adjacent to sylvian fissure...

lips, jaw, tongue, larynx...

one of 19 consonants follow by one of 3 vowels

bah,  faa, kee,  koo, zoo  eg

labial....   for  ba....   

but  da   uses coronal tongue  (roof of mouth)

dorsal tongue used :  guh...

use binary artic state variables...

buh  eg  uses  lips, laryn and jaw  but NOT  the tongue

sue...  is  0 1 01 1  /lips  tongue laryn jaw)

use this rich repertoire...

production of GAH...

from ecog data...

mm from  sylvian fissure...

labial is most doral  (near lip  representation)

coronal is lower and dorsal tongue  (guh) is lowest still.

look at high gamma  activity to assess...

use k nearest neighbor algo...

speech somatotopy  recapitulates the  homunculus...

but also find  dorsal laryngeal area (high up)

latencies are not difft across the central sulcus...

suggests broad integration of sens and motor func  during speech production.

how abt time course?

individual articulations have temporally specific correlations with high gamma...

lips get activ first then tongue then jaw then larynx then high tongue and back tongue...

summary:  control of artics is  somatotopic...  and
control is temporally sequenced...

fast feedback control  (cuz  simult activ of sensory and motor across central sulcus)

****

speech phonemes...

he shows video clip..

he will  map  time varying  gamma mapped onto cortical surface

first consonants then vowel...

BUH   see lips first then  larynx light up for UH...

DUH  see coronal tongue etc. areas...

he analyzes with PCA...(princip comps)

phonemes are combos of elemetary phonetic features...

major articulators  and constriciton   locations...

plosive like DUH  vs

fricative  SSHHHHH...

major articulators

DUH  coronal tongue...

is representation organizaed by acoustic props:  hale and chomsky 1991

vs  vocal  geometry  clement sand hume 1995...

vs  gestural theory...

look at cortical dendrogram...

look at subject 1  broken into 3 first prin comps...

results:   organiz by major oral articulators...
dorsal tongue, labial,   corononal tongue  (broken into  front tonue  like duh and luh   vs  
fricatives....

major articulators are primary organizng principle  then
contstric location  then constriciton..degree...

look at tempor dynamics  for front tongue and dorsal tonue
transitioning to a single vowel   ooooo.

eg  doo vs loo

summary

phon control is hierarch  organized accord to
major articulators  then
control location and
constriction degree..

first time...   repres of artic and phonemes...

*****
f0  is pitch of first formant  f0

formants are a proxy for vocal tract shape...

eg  diff btwn eee and ooo...

can use simple regularized formant decoders...

R2  = 0.81...
can predict from ratios of formants  eg  f2 / f1

vSMC  = ventral  supplemental motor cortex...

vowels are good proxy for shape of vocal tract but

consonants are NOT...  cannot disting bah and dah only on acoustics...

he works in Edward Chang  Lab...

Dave Conant  another collab

NATURE  last weeek  

Kristofer Bouchard...

Q1  why separ representations for larynx...

that is, why 2 separate  (high and low) laryng  areas)

func organiz of human sensorimotor cortex for speech artic...

ecog   can z scores of 10  (great in compar to fMRI)

Jay ... is there spatial smearing?

he uses 4 mm  center on electrodes   (usu ecog is 10 mm)

could pull out a lot of structure in dendrogram...

Q abt imagined speech...