Probing principles of large-scale object representation: Category preference and location encoding
Department of Psychiatry, Campus Charité Mitte, Charité-Universitätsmedizin Berlin, Germany. . Human Brain Mapping
(Impact Factor: 5.97).
07/2013; 34(7). DOI: 10.1002/hbm.22020
Knowledge about the principles that govern large-scale neural representations of objects is central to a systematic understanding of object recognition. We used functional magnetic resonance imaging (fMRI) and multivariate pattern classification to investigate two such candidate principles: category preference and location encoding. The former designates the preferential activation of distinct cortical regions by a specific category of objects. The latter refers to information about where in the visual field a particular object is located. Participants viewed exemplars of three object categories (faces, bodies, and scenes) that were presented left or right of fixation. The analysis of fMRI activation patterns revealed the following. Category-selective regions retained their preference to the same categories in a manner tolerant to changes in object location. However, category preference was not absolute: category-selective regions also contained location-tolerant information about nonpreferred categories. Furthermore, location information was present throughout high-level ventral visual cortex and was distributed systematically across the cortical surface. We found more location information in lateral-occipital cortex than in ventral-temporal cortex. Our results provide a systematic account of the extent to which the principles of category preference and location encoding determine the representation of objects in the high-level ventral visual cortex. Hum Brain Mapp, 2012. © 2012 Wiley Periodicals, Inc.
Available from: Matthias Guggenmos
- "The LOC ROI was defined as the intersection of the anatomical mask and the functional localizer based on the group-level T-contrast intact + split N scrambled at a significance level of p b 0.05 (family-wise error (FWE) corrected at the whole-brain level). Additionally we created separate ROIs for two subregions of LOC, lateral occipital cortex (LO; corresponding to the inferior and middle occipital anatomical masks) and posterior fusiform gyrus (pFus; posterior fusiform gyrus mask), based on previous reports regarding a possible functional dissociation between the two (Cichy et al., 2013; Grill- Spector et al., 2001). The V1 ROI was defined as the intersection of Brodmann's area 17 (derived from the SPM Anatomy toolbox; Eickhoff et al., 2005) and the functional localizer based on the group-level t-contrast intact + split + scrambled N implicit baseline at a significance level of p FWE b 0.05. "
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ABSTRACT: A fundamental issue in visual cognition is whether high-level visual areas code objects in a part-based or a view-based (holistic) format. Previous behavioral and neuroimaging studies that examined the view invariance of object recognition have yielded ambiguous results, providing evidence for either type of representational format. A critical factor distinguishing the two formats could be the availability of attentional resources, as a number of priming studies have found greater viewpoint invariance for attended compared to unattended objects. It has therefore been suggested that the activation of part-based representations requires attention, whereas the activation of holistic representations occurs automatically irrespective of attention. Using functional magnetic resonance imaging in combination with a novel multivariate pattern analysis approach, the present study probed the format of object representations in human lateral occipital complex and its dependence on attention. We presented human participants with intact and half-split versions of objects that were either attended or unattended. Cross-classifying between intact and split objects, we found that the object-related information coded in activation patterns of intact objects is fully preserved in the patterns of split objects and vice versa. Importantly, the generalization between intact and split objects did not depend on attention. We conclude that lateral occipital complex codes objects in a non-holistic format, both in the presence and absence of attention.
Available from: Alexa Morcom
- "The present context-selective SM effects for scenes in right PPA are also consistent with previous findings. A substantial literature links PPA to scene-selective visual processing (Epstein and Kanwisher, 1998; Cichy et al., 2013) as well as scene-selective item encoding (Brewer et al., 1998; Turk-Browne et al., 2006; Hayes et al., 2007; Awipi and Davachi, 2008; Prince et al., 2009; Preston et al., 2010) and two prior studies to scene-selective contextual encoding (Uncapher et al., 2006; Uncapher and Rugg, 2009). These findings support the view that enhanced sensory processing of context can increase the probability of its later recollection (Meiser and Sattler, 2007; Kuhl et al., 2012). "
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ABSTRACT: Recollection of events is accompanied by selective reactivation of cortical regions which responded to specific sensory and cognitive dimensions of the original events. This reactivation is thought to reflect the reinstatement of stored memory representations and therefore to reflect memory content, but it may also reveal processes which support both encoding and retrieval. The present study used event-related functional magnetic resonance imaging to investigate whether regions selectively engaged in encoding face and scene context with studied words are also re-engaged when the context is later retrieved. As predicted, encoding face and scene context with visually presented words elicited activity in distinct, context-selective regions. Retrieval of face and scene context also re-engaged some of the regions which had shown successful encoding effects. However, this recapitulation of encoding activity did not show the same context selectivity observed at encoding. Successful retrieval of both face and scene context re-engaged regions which had been associated with encoding of the other type of context, as well as those associated with encoding the same type of context. This recapitulation may reflect retrieval attempts which are not context-selective, but use shared retrieval cues to re-engage encoding operations in service of recollection.
Available from: Zhi Yang
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ABSTRACT: Multivariate pattern analysis (MVPA) is a recently-developed approach for functional magnetic resonance imaging (fMRI) data analyses. Compared with the traditional univariate methods, MVPA is more sensitive to subtle changes in multivariate patterns in fMRI data. In this review, we introduce several significant advances in MVPA applications and summarize various combinations of algorithms and parameters in different problem settings. The limitations of MVPA and some critical questions that need to be addressed in future research are also discussed.
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