SUMMER SCHOOL OF SCIENCEVIŠNJAN, 2003.

SPEECH PERCEPTION ANDCOCHLEAR IMPLANTS

Damir Kovačić

International School for Advanced Studies, Trieste&

SUVAG Polyclinic, ZAGREB

Language ------ >>>>> Speech Perception

One morning, when Gregor Samsa woke from troubled dreams, he found himself transformed in his bed into a horrible vermin. He lay on his armour-like back, and if he lifted his head a little he could see his brown belly, slightly domed and divided by arches into stiff sections. The bedding was hardly able to cover it and seemed ready to slide off any moment. His many legs, pitifully thin compared with the size of the rest of him, waved about helplessly as he looked.

from Franz Kafka: Metamorphosis

THE ESSENCE OF LANGUAGE:

**ARBITRARINESS OF THE SIGN

**INFINITE USE OF FINITE MEDIA

Language processing entails many types of knowledge (grammatical, lexical, phonological etc.) and representations (sentences, words, phonemes, etc.)

Linguistics, Psycholinguistics, Neuropsychology, Cognitive sciences, Information Theory, Neural Networks, etc……How are these processes and units represented in the brain?

Cognitive Neuroscience (Brain/Neuro Imaging)

To have a language:

A speaker/listener has stored knowledge (but where?)of about approximately ?????? words of his/her native language. This knowledge includes:

how the words sound the meaning of words the syntactic (grammatical) properties of words how to say/articulate words

MENTAL LEXICON -->>> HUGEEEEEE KNOWLEDGE!!!

UNIQUE TO HUMANS!

From Haagort’s talk

SPEECH PERCEPTION:

We will make a small experiment ;)

- to find out speech signal

- and its spectrum

Speech Perception:

Concerns the earliest stage in the language processing

when listener maps the time-varying acoustic signal

on discrete linguistics (more abstract) representations in brain

Phonemes (vowels and consonants)Syllables MorphemesWordsSentences

Word Segmentation

Categorical Perception

Perceptual Constancy- instantaneous adaptations to variations in speech

signal

SPEECH PERCEPTION – some basic phenomena

Coarticulation

Redundancy

The steady drip is worse than a drenching rain

NOISE AS SPEECH???

Ear Anatomy

Cochlea

• scalae vestibuli, media, tympani

• cochlear partition (Basilar membrane, organ of Corti)

• fluids: perilymph, endolymph

• Auditory neurons

• transforms sound into neural signals

• very sensitive organ, 35 mm long

• it looks like a snail’s house

Organ of Corti – the residence of hair cells

A

B

DC

TM

RL

PC

OHC

C Tectorial membrane

Reticular laminaStereocilia

Outerhair cells

Basilar membrane

Deiters’ cells

St

IHC

BM

St

(Inner hair cells) (Outer Hair cells)

IHC – aferent neurons (periphery brain), 4000

OHC – eferent neurons (brain periphery !!), 12000

“Travelling waves” in the cochlea

4000 Hz 400 Hz

Fluid

in motion

Fluid

at rest

40 dB

C

A

Stapes

Roundwindow

Basilar membrane

B

0 20 40 60 80 100 120 140

100

0

20

40

60

80

120

-20

Stimulus amplitude (dB SPL)

dB

re

. 1

µm

/se

c

Basilar membranevelocity

D

COCHLEAR IMPLANTS

Cochlear implantation shows a huge variability in its follow-up success and usefulness

Excellent and poor outcomes are attributable to the age of implantation:

1) Prelingually deafened children - excellent results

2) Prelingually deafened adults - poor, sometimes they demand the removal of the implant

THE RISE OF MACHINES: