Presentation on theme: "Form- and Meaning-based Priming Effects in fMRI H. Jamison*, L. Gonnerman §, P. Matthews* & J. Devlin* *Centre for Functional Magnetic Resonance Imaging."— Presentation transcript:
Form- and Meaning-based Priming Effects in fMRI H. Jamison*, L. Gonnerman §, P. Matthews* & J. Devlin* *Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, Oxford, UK § Department of Psychology, Lehigh University, Bethlehem, PA, USA 1. Background Skilled reading is a complex cognitive task, which engages a spatially distributed network of regions. Attempts to relate individual anatomical regions with particular types of processing typically rely on setting explicit judgement tasks, such as classifying a word based on form (orthography) or meaning (semantics). However, the results may be contaminated by strategic processing. Priming paradigms offer an alternative approach. They allow the relationship between words to be varied without the awareness of subjects, in order that strategic processing effects are avoided. Priming occurs when one word alters our reaction to another. If prime and target are related, this often leads to a response time advantage. Prime and target pairs may be related in: form orthography meaning semantics form + meaning morphology. 2. Current Study – Aims In this study we employed a visual masked priming paradigm to investigate automatic facilitation due to shared form and/or meaning, in a 2x2 factorial design, using event-related fMRI. 3. Paradigm 12 Subjects – healthy, right-handed, native British speakers. Aged 18-25 years [21±2], 7M/5F. Lexical Decision Task – had to decide whether target was word or non-word, and respond by button press. Rapid presentation and forward masking ensured subjects were unaware of primes. Stimuli presented as follows (Figure 1): * $%##$%$ conceal HIDE 1000ms 500ms 33ms 200ms LEXICAL DECISION: BUTTON PRESS 8. References * http://www.fmrib.ox.ac.uk/fslhttp://www.fmrib.ox.ac.uk/fsl Gonnerman, L. M., Andersen, E. A., & Seidenberg, M. S. (submitted). Graded semantic and phonological similarity effects in priming: Evidence for a distributed connectionist approach to morphology. Jenkinson, M., Bannister, P., Brady, M., & Smith, S. (2002). Improved optimization for the robust and accurate linear registration and motion correction of brain images. Neuroimage, 17(2), 825-841. Jenkinson, M., & Smith, S. M. (2001). A global optimisation method for robust affine registration of brain images. Medical Image Analysis, 5(2), 143-156. Josephs, O., & Henson, R. N. (1999). Event-related functional magnetic resonance imaging: Modelling, inference and optimization. Philosophical Transactions of the Royal Society, London B, 354, 1215-1228. Mechelli, A., Gorno-Tempini, M. L., & Price, C. J. (2003). Neuroimaging studies of word and pseudoword reading: consistencies, inconsistencies, and limitations. Journal of Cognitive Neuroscience, 15, 260-271. Wilson, J. L., Jenkinson, M., de Araujo, I., Kringelbach, M. L., Rolls, E. T., & Jezzard, P. (2002). Fast, fully automated global and local magnetic field optimization for fMRI of the human brain. Neuroimage, 17(2), 967-976. Woolrich, M. W., Ripley, B. D., Brady, J. M., & Smith, S. M. (2001). Temporal autocorrelation in univariate linear modelling of fMRI data. NeuroImage. 7. Acknowledgements This work was supported by funding from the Wellcome Trust & the MRC. HJ would like to thank the Wellcome Trust. We would also like to thank all subjects for their participation in the project. 6 Conditions – from which prime-target stimulus pairs were taken in pseudo-random order (Table 1). Figure 1 - Order of Stimulus Presentation Trials began with a fixation point, followed by forward mask, prime and finally target. Trials ended with lexical decision and button press, with inter-stimulus intervals being self-paced. 6. Conclusions Priming Paradigms are useful in defining implicit language processing regions. They demonstrate the partially separable effects of orthography and semantics, uncontaminated by strategic processing. Morphology does not affect any regions other than those affected by orthography and semantics. This is consistent with the claim that morphology is processed by the convergence of form and meaning. 5. Summary Response time is reduced significantly in orthographic and morphological conditions. Activation is reduced in several areas, for priming relative to the unrelated condition. Orthography and semantics affect left temporal regions - potential areas for processing meaning. Orthography also affects extra- striate regions implicated in form processing. Morphological priming effects were found in the bilateral angular gyrus. At a lower statistical threshold, morphology also reduced activation in posterior visual form areas and anterior temporal regions. 4. Results (i) Priming causes reductions in response time Subjects responded significantly faster to both orthographically and morphologically related word pairs, than to those which were unrelated (see Figure 2). A trend towards a priming effect occurred for semantically related word pairs. ConditionRelationshipExample Pair 1. Unrelated[-orth, -sem]legible-CROWN 2. Orthographically rel.[+orth, -sem]corner-CORN 3. Morphologically rel.[+orth, +sem]boldly-BOLD 4. Semantically related[-orth, +sem]cheerful-HAPPY 5. Pseudowords[-orth, -sem]banjo-HEEN 6. Non-words[-orth, -sem]viper-NDMG Table 1 – Experimental Conditions Image Acquisition – Gradient-echo EPI sequence (B 0 =3T, TR=3s, TE=30ms, 4x4x5mm). Images realigned and registered to MNI152 template, smoothed with 5mm FWHM Gaussian filter. FSL software* used to compute random effects model. Activations identified at Z>3.09, limited to areas engaged by word reading (i.e. those inclusively masked with a [unrelated words – non-words] contrast). Figure 2 – Behavioural Effects of Priming Mean change in response time (RT) in each priming condition, compared with unrelated word condition (given as 0ms for comparison). * indicates p<.05. Related in form Related in meaning -30 -20 -10 0 Orth Morph Sem Priming Condition Change in RT (ms) relative to unrelated word pairs ** (ii) Priming causes reductions in activation Region Affected by Priming Peak Z in each Condition OrthMorphSem Common to all priming: L angular gyrus188.8.131.52 R angular gyrus184.108.40.206 Form-based effects: L posterior fusiform3.78?? L ventral pre-motor3.16 Meaning-based effects: L middle temporal gyrus??3.28 Form * meaning interaction: L inferior temporal cortex3.103.31 Table 2 – Neural Correlates of Priming. Peak Z values of those areas activated in the word reading condition, which showed a reduction in activation in the priming conditions. (L = left, R= right). Several neural regions showed a decrease in activation under priming conditions, when compared with the unrelated word condition (see Table 2). (iii) Effect Sizes Figures 3 and 4 depict several of the regions affected by priming, and reveal the size of the changes in activation compared with the unrelated word pairs condition. Figure 3 – Neural Effects of Priming (a) Bilateral angular gyrus was affected by all three priming conditions. (b) The left posterior fusiform revealed a significant priming effect for orthographically related words a smaller effect for morphological pairs. Figure 4 – Neural Effects of Priming (a) There was a reliable priming effect in the left middle temporal gyrus (L. MTG) when words were semantically related and a trend for morphological pairs. (b) Both orthographic and semantic priming affected left inferior temporal gyrus (L. ITG). a b a b Orth Morph Sem Priming Condition % BOLD signal change relative to unrelated word pairs 0.0 -0.2 -0.4 Orth Morph Sem Priming Condition % BOLD signal change relative to unrelated word pairs 0.0 -0.2 -0.4 Orth Morph Sem Priming Condition % BOLD signal change relative to unrelated word pairs 0.0 -0.2 -0.4 Orth Morph Sem Priming Condition % BOLD signal change relative to unrelated word pairs 0.0 -0.2 -0.4 - Bilateral angular gyri L. posterior fusiform L. MTG L. ITG
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