Audrey Kittredge 593: Neuroimaging of Language

1. Short-Term Reorganization of Auditory Analysis Induced by Phonetic ExperienceLiebenthal et al. (2003). JoCN. Audrey Kittredge 593: Neuroimaging of Language

2. MRI: physics • Hydrogen nuclei act as magnets (spinning, charged particle)

3. MRI: physics • In strong magnetic field: spin-axes form vector parallel to field

4. MRI: procedure • Radio Frequency pulse • Changes direction and strength of vector • Eventually, nuclei relax and vector returns to original position • As nuclei relax, give out pulse • Pulse type depends on water/fat ratio of tissue --> MRI images!

5. Functional MRI • Hemoglobin shows up better than deoxyhemoglobin on MRI SO • Brain areas with more oxygenated blood will show up better (BOLD)

6. Connection to neural activity? • Increase in net neural activity --> increase in oxygenated blood supply (slow) • Quick succession of images: BOLD signal at various times

7. Pros • Good spatial resolution • Less risky, faster acquisition than PET • Event-related design

8. Cons • Poor temporal resolution • BOLD signal degraded near air/bone boundary • Movement artifacts • High speed data acquisition = noisy!

9. Phonetic perception • How does this occur? • Automatic phonetic analysis module (Liberman & Mattingly, 1989) • Stimulus-independent auditory analysis (Kluender & Greenberg, 1989)

10. Past Research • PET, fMRI studies • Speech vs nonspeech: superior temporal cortex

11. Problem! • Confound: perception or stimuli? • Goal: study perception mode independent of stimulus properties • How do we do this?…

12. …Sinewave speech! • Sinewave example

13. Original sentence • “The steady drip is worse than a drenching rain”

14. Sinewave speech: properties • Sinusoid fit to center frequency and amplitude (over time) of F1-F3 or F4 • Result: rapidly changing pure tones • Lack fine-grained acoustic properties of speech

15. Past studies on sinewave speech • Remez et al. (1981): • “Describe”: most say non-speech • “Transcribe”: most write all/some of sentence correctly

16. Tone-matching Task(Remez et al., 2001) • Stimuli • Sinewave word e.g. juice • Isolated T2 from T123/4 complex • Task: is tone constituent of complex? • Listeners can do this… • When uninformed (not speech) • While matching tone complex to printed word • Difficult task!

17. Creation of stimuli • Phonetic stimulus (sinewave word) • 3 lowest formants = 1 sinewave each • Tone probe • “True”: from word • “False”: from other sinewave word • Nonphonetic stimulus • T1 and T3 temporally reversed

18. Spectrogram of Stimuli

19. Pilot studies • Phonetic transcribed 52.1% accuracy, multiple choice 89.5% accuracy • Rated as “Clearly identifiable word”: • 61% phonetic • 22% nonphonetic • “Nonspeech”: • 58% nonphonetic • 20% phonetic

20. Stimuli: summary • 288 stimuli total • 108 pairs of phonetic, nonphonetic stimuli • 1/3 repeated • 1/2 trials = false

21. Experimental Design Practice Naïve 1 Naïve 2 Phonetic Practice Informed 1 Informed 2

22. Procedure • Practice • Stimuli: arbitrarily composed sinusoids • Sinewaves: same/diff pitch contour? • Tone-matching task (T2-T1234) • Naïve condition • “single tone”, “tone complex” • 2 blocks

23. Procedure • Phonetic practice • Sinewave stimuli: 8 sentences, 18 words • Chose from 4 transcriptions • Feedback given for every 5th sentence • Accuracy data collected • Informed condition • “words” • 2 blocks

24. Results: RT • Phonetic: • Test Block p < .o4 (N1-N2 p < .02, N2-I1 p < .03, I1-I2 p < .05) • Nonphonetic • Test Block p < .001 (N1-N2 p < .01) • In naïve condition, effect of stimulus type p < .04

25. Results: Accuracy • Phonetic: • No significant effect of Test Block p < .11 • Nonphonetic • No significant effect of Test Block p < .53 • In naïve condition, no effect of stimulus type p < .07

26. Results: Phonetic Form Practice • Sentence task: 84 +/- 21% accuracy • Words: 60 +/- 16% accuracy • Chance = 25% in both tasks

27. Results: Subjective Reports • 29/31 unaware of phonetic quality during naïve blocks • 13/31 recognized words during informed blocks

28. Conclusions: Behavior • Phonetic awareness interferes with task • Naïve: subjects perceived only auditory form • Informed: subjects perceived both, focused on auditory • NO explanation for stimulus RT difference in Naïve

29. Within each block… 9s 9s 9s 9s 9s 9s 9s 9s 2 phonetic trials 2 nonphonetic trials Baseline (silence) Clustered image acquisition

30. Image acquisition • 18 images per trial type per block • 36 images per condition/trial type • E.g. Naïve, phonetic

31. fMRI Images • 16 slices: • Axially oriented (horizontal) • Contiguous • 3x3x4mm voxels • Slice coverage: • Most of temporal lobes • Part of frontal and parietal lobes • Occipital lobe • Anatomical (MRI) images (1x1x1mm)

32. fMRI analysis: individuals • AFNI software package • Trial - Baseline-->BOLD difference maps • Difference maps: • averaged (BOLD vs baseline) • Voxel-wise ANOVA (sorted by trial type and condition)

33. fMRI analysis: averaging • Individual statistical maps transformed into standard space • Talairach brain • Complicated statistics, smoothing… • t values at each voxel averaged across subjects

34. fMRI analysis: significance testing • Randomization testing: • t values >/= .37 significant • uncorrected voxel-wise p < .001 • Activation foci < 300 microL removed

35. fMRI Result Summary

36. fMRI Images

37. Phonetic: Informed-Naive • Left Heschl’s gyrus (HG/BA42) • Left posterior superior temporal gyrus (STG/BA 42/22) • Right HG/BA42

38. Phonetic Experience • Decreased activation = decreased task execution • Underlies reduced performance • Interference masks information like noise • STG • Primate HG/post STG analogues involved in complex sound analysis, auditory STM • Left-lateralized • Specialization for speech

39. Phonetic Experience cont’d • No shift to other areas • No conscious phonetic perception • Phonetic experience induces “short-term functional reorganization of auditory analysis” and is contingent on “dynamic structure”

40. Phonetic: Informed-Naive • Dorsomedial thalamic nucleus • Superior frontal gyrus (BA8) • Left middle frontal gyrus (MFG/BA10)

41. Unexplained Results • Dorsomedial thalamic nucleus, medial prefrontal cortex: • Areas with reciprocal connections to each other and ST area • Connected neural system… • Engaged in task • Sensitive to interference

42. Nonphonetic: Informed-Naive • Left posterior STG (BA 42/22)

43. Phonetic: Blocks2-Blocks1 • Left middle frontal gyrus (BA9)

44. Nonphonetic: Blocks1-Blocks2 • Left inferior frontal gyrus (IFG/BA44)

45. Proficiency Effects • Left IFG, MFG: • Initial difficulty in verbal production task (Raichle et al., 1994) • Not cause of Informed-Naïve difference (no anatomical overlap)

46. What do YOU think?

47. Conclusions…? • “Centrality” of this function • Naïve: Phonetic vs nonphonetic RT • Reorganization contingent on speech? • Decreased activation: underlies reduced performance? • Proficiency/Informed: frontal overlap?

48. Methodology…? • Response/accuracy inclusion criteria? • RT/accuracy data not parallel • RT: correct, incorrect, true, false trials • Word length? • Age variation (18-57)? • Naïve: phonetic vs nonphonetic? (fMRI)

49. Some questions… • Role of thalamus/medial frontal areas? • Task difficulty --/--> activation increase

50. Some more questions… • Given phonetic practice, is reorganization entirely stimulus-driven? • How generalizable to normal speech-nonspeech analysis? • Original question: automatic phonetic module or auditory analysis?