An fMRI investigation of covertly and overtly produced mono- and multisyllabic words.

1. Brain and Language 93 (2005):20-31. An fMRI investigation of covertly and overtly produced mono- and multisyllabic words. Shuster LI, Lemieux SK.

2. The Insula: what is it? • An forgotten island of cortex hiding behind the lateral fissure • Ill-defined functions may include • Visceral sensory • Vestibular • Motor • Supplementary motor • Speech movements

3. Background: Speech and the Insula Non-AOS AOS • Left anterior insular damage linked to acquired apraxia of speech (AOS) (Dronkers, 1996) • AOS characterized as, "a disorder in the motor planning of articulatory movements” • Lesion-overlap method • 25 chronic stroke patients with AOS • 19 patients non-AOS aphasics • Hence, “this area seems to be specialized for the motor planning of speech“

4. Background: Speech and the Insula • Insular damage-AOS correlation does not appear to hold for acute-stage stroke patients (Hillis et al., 2004) • Insula currently thought to be involved in motor movements of speech • E.g. coordination of muscle movements rather than planning(Ackermann & Riecker, 2004)

5. Shuster and Lemieux (2005) Overview • Goal: • Examine the role of the insula in overt and covert speech production • Methods: • fMRI Blood Oxygenation Level Dependent (BOLD) responses • Overtness contrast • Syllabic-length contrast • Logic: • Overtness contrast should identify general overt speech areas • Syllable-length contrast should show specific areas with graded activation in motor planning of utterances

6. Shuster and Lemieux (2005): Methods Behavioral task: • Participants (n=10) auditorily prompted to overtly or covertly “say” individual words • 30 monosyllabic nouns • 30 tetrasyllabic nouns • Words frequency-matched à la Thorndike and Lorge (1944) • (No additional behavioral tasks; no behavioral measures taken)

7. Repeat the word to yourself as quickly as you can, without moving any part of your mouth. Just hear yourself saying the word inside your head. Be careful not to move any part of your mouth and try not to swallow during the response time

8. Criticisms of Materials • Length likely confounded with concreteness • Thorndike-Lorge? But do either of these criticisms really matter here? -Length effects may be difficult to interpret.

9. Criticisms of the tasks • Image-naming or stem-completion would have been a better task • Phonological vs. articulatory rehearsal • Participants may have been ‘sleeping’ in covert trials • A behavioral measure was needed • Covert-subtraction-based differences difficult to interpret

10. Shuster and Lemieux (2005): Methods Design details: • Event-related design • Allows isolation of speech/motion artifacts • Requires long ISIs (1250 ms!) • Overt and covert response blocks of 12.5 minutes each • All words presented in each block • Randomized word orders • Block order counterbalanced between subjects

11. Shuster and Lemieux (2005): Methods Imaging details: • 1.5T scanner • Anatomical scans • .86 x .86 x 1.2mm voxels • Functional scans • 20 interleaved axial slices acquired • 3.43 x 3.43 x 5 mm voxels • No baseline • BOLD responses analyzed via AFNI • Subtraction methods for overtness and length

12. Shuster and Lemieux (2005): Methods An interesting analysis detail… • “the stimulus time series was convolved with a gamma variate function” • Translation: speech-motion artifacts removed by correlating observed data with an idealized ‘motion artifact’ function

13. Shuster and Lemieux (2005): Results Overview of results • More overall activity in overt than covert speech • Included more activity in general cognitive regions • More overall activity in multisyllabic than monosyllabic word production

14. Shuster and Lemieux (2005):Results Overt > Covert Overtness effects Covert > Overt

15. Shuster and Lemieux (2005):Results Mono- > Multisyllabic Mono- vs. Multisyllable effects Multi- > Monosyllabic

16. Shuster and Lemieux (2005): Discussion Left Insula • More active in overt speech • No more active with longer words • Active in speech production but maybe not in sequencing speech movements

17. Shuster and Lemieux (2005): Discussion Left inferior parietal lobule (and the left parietal cortex in general) • More active with longer (overt) words • Consistent with previous production and apraxia studies • Indicates involvement in word-length dependent processes (e.g. articulatory planning, sequencing, monitoring)

18. Shuster and Lemieux (2005): Discussion Left Superior Temporal Sulcus (STS) • More active in overt speech • No more active with longer words • Activity may reflect perception of self-generated speech • Confounded by auditory stimulus presentation

19. Shuster and Lemieux (2005) Conclusions: • Covert and overt speech produced qualitatively different response patterns, including more activation of general cognitive regions, suggesting that covert production may not be a good substitute for overt production

20. Shuster and Lemieux (2005) Conclusions: • The left insula is active in overt speech production, but shows no utterance-length-dependent effects, suggesting a revised role in overt speech production • The left parietal cortex, however, does show more length-related activity

21. Shuster and Lemieux (2005) Questions for discussion • Any thoughts on the role of the insula in speech? • Monitoring in the left inferior parietal cortex? • What might have been happening in the “inner speech condition? • How might this change our interpretation of overt vs. covert results? • Occipital activation?

22. “Clearly, as Bennett and Netsell (1999) noted, further studies are required before the specific role of the left insula in speech production can be established” --Shuster and Lemieux (2005)