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Discrimination of self-similar visual hierarchies activates the parieto-medial temporal pathway
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Mauricio Martins1, Florian Ph.S Fischmeister2,3, Estella Puig-Waldmueller1, Jinook Oh1, Alexander Geißler3, Roland Beisteiner2,3, Tecumseh Fitch1
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Complex hierarchical structures play a central role in many aspects of human cognition, prominently including both language and music [1]. A promising method to represent complex hierarchical structures - realized in nature and attractive for experimental research - is recursion. Recursion is a self-referential process by which infinite use can be made of finite means [2].
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Introduction
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1 Department of Cognitive Biology, University of Vienna, Vienna, Austria; 2 Study Group Clinical fMRI, Department of Neurology, Medical University Vienna, Vienna, Austria; 3 High Field MR Centre of Excellence, Medical University of Vienna, Vienna, Austria
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Figure 3: Brain activation contrast between recursive (cross-level; shown in red) and non-recursive (within-level; shown in blue) hierarchical tasks. Results are presented at P < 0.05 with FDR correction.
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[1] Fitch, W. T., & Friederici, A. D. (2012). Artificial grammar learning meets formal language theory: An overview. Philosophical Transactions of the Royal Society B: Biological Sciences, 367(1598), 1933-1955. [2] Martins, M. D. (2012). Distinctive signatures of recursion. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 367(1598), 2055–64. [3] Kravitz, D. J., Saleem, K. S., Baker, C. I., & Mishkin, M. (2011). A new neural framework for visuospatial processing. Nature reviews. Neuroscience, 12(4), 217–30. [4] Martins M. J., Fishmeister, F., Puig Waldmüller, E., Oh, J., Geissler, A., Fitch W. T., Beisteiner R (2014). Fractal Image Perception provides Novel Insights into Hierarchical Cognition. NeuroImage, 96, 300-308. [5] Ranganath, C., & Ritchey, M. (2012). Two cortical systems for memory-guided behaviour. Nature Reviews Neuroscience, 13(10), 713-726. [6] Binder, J. R., Desai, R. H., Graves, W. W., & Conant, L. L. (2009). Where is the semantic system? A critical review and meta-analysis of 120 functional neuroimaging studies. Cerebral Cortex, 19(12), 2767-2796.
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Figure 1: Brain activations specific for both recursive (cross-level) and non-recursive (within-level) hierarchical tasks, in comparison with a simple similarity baseline. Results are presented at P < 0.05 with FDR correction.
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Contact: Mauricio Martins,
[email protected] Department of Cognitive Biology, University of Vienna, Vienna, Austria
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This study was supported by the Austrian Science Fund (P23611)
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This work was supported by the research cluster grant “Shared Neural Resources for Music and Language” (University of Vienna and Medical University of Vienna).
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In this study [4] we investigated the brain circuits active during the discrimination of hierarchies generated by rule-based processes. We contrasted a rule that adds elements to fixed hierarchical levels with a rule that generates new self-similar levels. We found that within-level hierarchical transformations activate to a greater extent regions involved in visuo-spatial processing [3]. On the other hand, processes that generate new self-similar hierarchical levels activate neural circuits involved in the integration of objects in contexts, and in semantic processing [3, 5, 6]. The generation of self-similar hierarchies in the visuo-spatial domain seems to require the integration of the ‘where’ information with the ’what’ information.
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Figure 1: Examples of Visual Recursion Task (VRT) stimuli (showing cross-level transformations), Embedded Iteration Task (EIT) stimuli (showing within-level transformations), and PSVT (Positional Similarity Visual Task) stimuli (a simple matching to sample baseline).
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Our main findings were the following: 1) Both hierarchical tasks (recursive and non-recursive) activated a bilateral network (the dorsal stream) which includes visual association areas and fronto-parietal circuits associated with spatial reasoning (Fig.2); 2) Compared to non-recursive processes, the representation of self-similarity rules generating new hierarchical levels recruited regions within the parieto-medial temporal pathway - including the posterior cingulate cortex and retrosplenial cortex - and their projections to the medial temporal cortex, which have been associated with the integration of spatial and categorical information [3]. We also found activations in the anterior portions of superior and middle temporal gyri (Fig.3); 3) In contrast, within-level non-recursive rules activated more strongly the dorsal stream, and the dorsal fronto-parietal network (Fig.3).
References
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Image processing performed using SPM8 including slice-time correction, correction for motion, spatial normalization and smoothing. Task related activations were individually modeled and then submitted to a repeated measure GLM.
Results
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Fourty subjects (19 male, aged 20-32y) participated in this study. Functional images were acquired on a 3 Tesla TIM Trio system (Siemens, Erlangen, Germany) using single-shot gradient-echo EPI. 36 slices (2.7 mm thickness and 20% gap) were aligned AC-PC with a matrix size of 128x128, a FOV of 220 and TE/TR of 32/2200 ms. To investigate the neural circuits associated with the representation of non-recursive and recursive rules, we adapted the Visual Recursion Task and the Embedded Iteration Task as described in [4].
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In this study, we addressed hierarchy in the visual domain, using a novel paradigm based on fractal images [2]. We compared brain activity across three different tasks: a similarity task, and two hierarchical tasks in which subjects were asked to recognize the repetition of a rule operating transformations either within an existing hierarchical level (non-recursive), or generating new hierarchical levels (recursive). Similar hierarchical images were generated by both rules (Fig.1).
