Two pre-tests were conducted before scanning to verify the efficacy of our visual masking

1. #MO16 Is morphology a fundamental component of language? J. T. Devlin1,H. L. Jamison1, P. M. Matthews1, L. M. Gonnerman2 1Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, U. K. 2Department of Psychology, Lehigh University, PA, U. S. A. Imaging Results: Lexical Decision Summary Morphological Priming: Left middle temporal gyrus Morphology is the aspect of language concerned with the internal structure of words, but it is not clear whether morphology is a basic element of linguistic structure or whether it emerges from systematic regularities between the form and meaning of words. Here we looked for evidence of morphological structure at a neural systems level using a visual masked priming paradigm and functional magnetic resonance imaging (fMRI). Form and meaning relations were manipulated in a 2  2 design to identify reductions in BOLD signal related to shared form (corner-corn), to shared meaning (idea-notion), and to shared morphemes (boldly-bold, which overlapped in both form and meaning). Relative to unrelated pairs (ozone-hero), morphologically related items reduced activation in posterior angular gyrus bilaterally, left occipito-temporal cortex, and left middle temporal gyrus. In the posterior angular gyrus region, a reduction in activation was observed for all three priming conditions, possibly reflecting reduced attentional demands rather than overlapping linguistic representations per se. In contrast, the reductions seen in the left occipito-temporal cortex and left middle temporal gyrus corresponded, respectively, to main effects of orthographic and semantic overlap. In other words, the most significant finding of our experiment is that the neural regions sensitive to morphological structure appear to overlap almost entirely with regions sensitive to orthographic and semantic relatedness, suggesting that morphology emerges from the convergence of form and meaning. • The initial analysis of the imaging data identified the neural circuit engaged in word reading by contrasting Unrelated pairs to Consonant letter strings Figure 4: Regions activated by Unrelated > Consonants shown on the group mean structural scan in standard space. Scanned using gradient echo EPI, B0=3T, TR = 3sec, TE = 30msec, FOV = 192 × 256mm, matrix = 64 × 64. Images were realigned to correct for head motion, registered to the MNI-152 template, and smoothed with a 5mm FWHM Gaussian kernel. RFX are shown with voxel thresholding at Z > 3.09. • This revealed activation in several areas including the: 1) left frontal operculum, 2) left precentral gyrus, 3) posterior angular gyrus, bilaterally, 4) left posterior occipito-temporal cortex, and 5) left middle temporal gyrus (not shown). consistent with previous lexical decision experiments (1-3). • Within this system, we looked for reductions in BOLD signal for the morphological priming condition relative to the unrelated condition. These were identified in the angular gyrus, posterior occipito-temporal cortex, and middle temporal gyrus (Figures 5-7). • No increases in BOLD signal were observed for any priming conditions. • There was a significant BOLD signal reduction for semantically related pairs in a region of the left middle temporal gyrus (–70, –42, 4; Z=3.3), which also showed a smaller effect for morphologically related pairs (Z=2.6; Figure 7). Figure 7: Neural priming effects in the left middle temporal gyrus. • There was a significant main effect of Meaning (F1,21=4.4, p<0.05) and a significant interaction (F1,21=8.3, p<0.01) but no effect of Form (F1,21=1.1). • Despite a comparable mean reduction in BOLD signal, no effect was seen for orthographic relatedness due to greater variance between subjects. Thus, both semantically and morphologically related word pairs significantly reduced BOLD signal in this region. L L R 2 3 2 1 4 3 X = -40 Z = 26 Current Study • 11 native British English speakers participated in a visual masked priming experiment using lexical decision(Figure 1) Figure 1: A schematic diagram of the visual masked priming paradigm. The prime was forward masked by a visual noise pattern and backward masked by the target. Lexical stimuli were matched for familiarity, frequency, imageability and syllable length, while all stimuli were matched for letter length. • The experiment used a 2 × 2 factorial design where prime-target pairs were related in Form [± Orth] and/or Meaning [± Sem] (Table) Prediction:  If morphology is a separate form of linguistic information, then we would expect to see evidence of its contribution to word recognition above and beyond the effects of form and meaning (i.e. a significant supra-additive interaction).  On the other hand, if morphology arises from the convergence of form and meaning, then we would expect brain regions sensitive to morphological structure to overlap with those showing sensitivity to orthographic and/or semantic structure. 1500ms PASS 200ms Discussion passive 33ms $%##&@#@ 500ms • Like previous studies (4), we found significant behavioural priming effects for morphologically related word pairs, indicating that participants could benefit from the prime-target relation despite not being consciously aware of the prime. • Results demonstrate several neural regions sensitive to “morphological” relations between prime and target word pairs 1. Posterior angular gyrus: We observed reduced BOLD signal for all three priming conditions but no effect of morphology beyond that of form and meaning. In addition, in all three priming conditions response latencies decreased relative to the unrelated condition, suggesting the common reduction in activation may reflect reduced attentional demands, rather than overlapping linguistic representations per se (5-7). 2. Left occipito-temporal cortex: There was reduced BOLD signal for word pairs sharing Form (i.e. Orthographic and Morphologically related conditions), suggesting the effect may be due to orthographic overlap. This is consistent with many studies implicating this region in visual form processing (8-11). 3. Left middle temporal gyrus: We found significantly reduced activation for semantically related word pairs (i.e. Semantic and Morphologically related conditions). This is a multi-modal association area sensitive to both auditory and visual input (12,13) and is engaged in semantic processing regardless of the input (14). • The most significant finding of our experiment is that the neural regions sensitive to morphological relatedness appear to overlap almost entirely with regions sensitive to orthographic and semantic relatedness. Power analyses demonstrated that this experiment had a sensitivity of 0.8 or greater for detecting neural priming effects, based on the effect sizes (ranging from 0.13-0.38% signal change) and standard deviations (ranging from 0.18-0.44%) observed in the current experiment. Thus, while one cannot rule out the possibility that regions not detected in this study also may contribute to morphological processing, the current findings are strikingly consistent with the claim that morphology emerges from the convergence of form and meaning. Time * 1000ms Morphological Priming: Posterior Angular Gyrus • Morphological priming led to a reduced BOLD signal in the posterior angular gyrus, bilaterally (Figure 5) Figure 5: Neural priming effects in the posterior angular gyrus. The effects are color-coded to indicate the condition which led to the reduction. White indicates a significant priming effect in all three conditions. The adjacent bar plots illustrate the mean percent BOLD signal change in the region between each priming condition and the unrelated baseline. • There was: 1. a significant main effect of Meaning (F1,21=5.7, p<0.05), 2. a marginal effect of Form (F1,21=3.1, p<0.1), and 3. a significant interaction (F1,21=12.8, p<0.01). The morphological priming effect was significantly smaller than expected in light of the main effects of Form and Meaning (i.e. a sub-additive interaction). Table: Conditions and sample stimuli in the lexical decision task Condition Example Relation 1. Unrelated event – RUG [–Orth, –Sem] 2. Orthographic winsome –WIN [+Orth, –Sem] 3. Semantic profit – GAIN [–Orth, +Sem] 4. Morphological hunter – HUNT [+Orth, +Sem] 5. Pseudo-words dollar – TAVE None 6. Consonant strings brutally – PLB None Behavioural Results • Two pre-tests were conducted before scanning to verify the efficacy of our visual masking • Performance was at ceiling for words presented for 200msec. In contrast, words presented for 33msec were nearly impossible to perceive. Only 4/220 words were read aloud and performance on the matching task was not different from chance (binomial test, p=0.98). • These results demonstrate the efficacy of the visual masking used here. Task: 1. Read the word aloud, 2. Select the word between the if possible. masks. If uncertain, guess. WAVE MUST #$%%#$ #$%%#$ 500ms cast wave 33 or 200ms $%##$% $%##$% 500ms * * 1000ms Time Morphological Priming: Left occipito-temporal cortex Figure 2: Behavioural pre-tests. On the left is a schematic of the reading task while the right shows the forced choice masking task. In both, words were presented for either 33 or 200msec between visual masks. References 1. Binder, J. R. et al. (2003). Neural correlates of lexical access during visual word recognition. J Cogn Neurosci, 15(3), 372-393. 2. Price, C. J., Wise, R. J., Watson, J. D., Patterson, K., Howard, D., & Frackowiak, R. S. (1994). Brain activity during reading: The effects of exposure duration and task. Brain, 117(6), 1255-1269. 3. Rumsey, J. M., Horwitz, B., Donahue, B. C., Nace, K., Maisog, J. M., & Andreason, P. (1997). Phonological and orthographic components of word recognition: a PET-rCBF study. Brain, 120(5), 739-759. 4. Taft, M., & Forster, K. (1975). Lexical storage and retriveal of prefixed words. Journal of Verbal Learning and Verbal Behavior, 14, 638-647. 5. Constantinidis, C., & Steinmetz, M. A. (2001). 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Multiple levels of visual object constancy revealed by event related fMRI of repetition priming. Nature Neuroscience, 5(5), 491-499. 12. Cardillo, E., Utman, J. A., Matthews, P. M., & Devlin, J. T. (in press). Left inferior prefrontal cortex activity reflects inhibitory, rather than facilitatory, priming. Journal of Cognitive Neuroscience. 13. Devlin, J. T., Matthews, P. M., & Rushworth, M. F. (2003). Semantic processing in the left inferior prefrontal cortex: a combined functional magnetic resonance imaging and transcranial magnetic stimulation study. J Cogn Neurosci, 15(1), 71-84. 14. Vandenberghe, R., Price, C. J., Wise, R., Josephs, O., & Frackowiak, R. S. J. (1996). Functional anatomy of a common semantic system for words and pictures. Nature, 383, 254-256. • There was a significant BOLD signal reduction for orthographically related pairs in a region of the left posterior occipito-temporal cortex (–44, –60, –18, Z=3.8), which also showed a smaller effect for morphologically related pairs (Z=2.7; Figure 6). Figure 6: Neural priming effects in the left occipito-temporal junction. The adjacent bar plots illustrate the mean percent BOLD signal change in the region between the priming conditions and the unrelated baseline. • There was a significant main effect of Form (F1,21=15.2, p<0.001) but no effect of Meaning (F1,21<1), and a marginal interaction (F1,21=3.8, p<0.1) Both orthographically and morphologically related word pairs reduced BOLD signal in this region, although the reduction was smaller for morphologically related words. Figure 3:Behavioural results of the main lexical decision task. Lexical conditions are in grey and non-lexical in black. • There was a significant main effect of Form (F1,10=8.2, p<0.05) indicating that when prime-target pairs shared visual form, this facilitated responses. No other effects were significant. * * • Planned comparisons revealed significant priming effects for Morphologically related (t10=3.0, p<0.01) and Orthographically related (t10=2.7, p<0.05) word pairs relative to unrelated pairs.