An fMRI investigation of covertly and overtly produced mono- and multisyllabic words.The Insula: what is it?Background: Speech and the InsulaSlide 4OverviewBehavioral task:Slide 7Criticisms of MaterialsCriticisms of the tasksDesign details:Imaging details:An interesting analysis detail…Overview of resultsShuster and Lemieux (2005): ResultsSlide 15Left InsulaLeft inferior parietal lobule (and the left parietal cortex in general)Left Superior Temporal Sulcus (STS)Slide 19Slide 20Questions for discussionSlide 22An fMRI investigation of covertly and overtly produced mono- and multisyllabic words.Shuster LI, Lemieux SK.Brain and Language 93 (2005):20-31.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 movementsBackground: Speech and the Insula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“ AOSNon-AOSBackground: 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)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 utterancesShuster and Lemieux (2005)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)Shuster and Lemieux (2005): MethodsRepeat 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 timeBut do either of these criticisms really matter here? -Length effects may be difficult to interpret.Criticisms of MaterialsLength likely confounded with concreteness Thorndike-Lorge?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 interpretShuster and Lemieux (2005): MethodsDesign 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 subjectsShuster and Lemieux (2005): MethodsImaging 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 lengthShuster and Lemieux (2005): MethodsAn 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’ functionOverview 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 productionShuster and Lemieux (2005): ResultsShuster and Lemieux (2005):ResultsOvertness effectsCovert > OvertOvert > CovertMono- vs. Multisyllable effectsMono- > MultisyllabicMulti- > MonosyllabicShuster and Lemieux (2005):ResultsLeft InsulaMore active in overt speechNo more active with longer wordsActive in speech production but maybe not in sequencing speech movementsShuster and Lemieux (2005): DiscussionLeft 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)Shuster and Lemieux (2005): DiscussionLeft 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 presentationShuster and Lemieux (2005): DiscussionConclusions: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 productionShuster 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 activityShuster 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?Shuster and Lemieux (2005)“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