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SUMMARY:Neural foundations of spoken language: word learning and ambiguity
  resolution - Matt Davis\, University of Cambridge\, MRC Cognition and Bra
 in Sciences Unit.
DTSTART:20080122T160000Z
DTEND:20080122T173000Z
UID:TALK10350@talks.cam.ac.uk
CONTACT:Napoleon Katsos
DESCRIPTION:Understanding spoken language requires a complex series of pro
 cessing stages to perceive speech sounds\, recognise familiar words and co
 mbine word meanings for comprehension. I will begin by sketching out an ac
 count of the multiple\, hierarchically-organised processing streams in the
  temporal lobe\, and convergent connectivity in prefrontal/premotor region
 s that are involved in understanding speech. From this anatomical starting
  point\, I will present two case studies of how investigations of these ne
 ural foundations can contribute to a cognitive and computational understan
 ding of spoken language processing. \n\nThe first half of the talk will ex
 plore the processes involved in learning new words. Existing findings sugg
 est a two stage process in which phonological representations of novel wor
 ds are rapidly acquired\, but require offline consolidation before they ac
 hieve equivalent lexical status as pre-existing familiar words. In behavio
 ural experiments only novel words learnt on the previous day to testing en
 gage in lexical competition and show faster repetition latencies than untr
 ained nonwords. In fMRI\, neural responses to novel words showed evidence 
 for overnight consolidation with responses in superior temporal\, premotor
  and cerebellar regions being unmodified by training on the same day as sc
 anning whereas novel words learnt on the previous day show more word-like 
 neural responses. In contrast\, elevated responses to novel words in the l
 eft hippocampus show rapid habituation and predict the initial acquisition
  of unfamiliar novel words. These findings suggest an account of word lear
 ning in which there is a division of labour between hippocampal and cortic
 al systems involved in the initial acquisition and overnight consolidation
  of novel spoken words. Biological precedents for this two-stage learning 
 process will be discussed. \n\nThe second half of the talk will report evi
 dence from functional imaging investigations of semantic ambiguity resolut
 ion. We will first of all provide evidence for a coordinated response of i
 nferior frontal and inferior temporal lobe regions in computing the correc
 t meaning for sentences such as “The shell was fired towards the tank”
 . This fronto-temporal response to ambiguity provides a neural marker for 
 intact speech comprehension which can be applied to clinical and pharmacol
 ogical states in which behavioural responses to speech are absent. Dissoci
 ations of frontal and temporal lobe responses to speech during sedation wi
 th anaesthetic drugs suggest a critical role for frontal regions in suppor
 ting the perception and comprehension of speech. In severely brain injured
  patients (e.g. vegetative and minimally-conscious patients) functional im
 aging can detect residual speech comprehension that would not have been de
 tected with behavioural responses. Such findings raise important questions
  concerning the relationship between speech comprehension and conscious aw
 areness. 
LOCATION:GR-06/07\, English Faculty Building
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