Object Representations for Multiple Visual Categories Overlap in Lateral Occipital and Medial Fusiform Cortex

How representations of visual objects are maintained across changes in viewpoint is a central issue in visual perception. Whether neural processes underlying view-invariant recognition involve distinct subregions within extrastriate visual cortex for distinct categories of visual objects remains unresolved. We used event-related functional magnetic resonance imaging in 16 healthy volunteers to map visual cortical areas responding to a large set (156) of exemplars from 3 object categories (faces, houses, and chairs), each repeated once after a variable time lag (3-7 intervening stimuli). Exemplars were repeated with the same viewpoint (but different retinal size) or with different viewpoint and size. The task was kept constant across object categories (judging items as "young” vs. "old”). We identified object-selective adaptation effects by comparing neural responses to the first presentation versus repetition of each individual exemplar. We found that exemplar-specific adaptation effects partly overlapped with regions showing category-selective responses (as identified using a separate localizer scan). These included the lateral fusiform gyrus (FG) for faces, parahippocampal gyrus for houses, and lateral occipital complex (LOC) for chairs. In face-selective fusiform gyrus (FG), adaptation effects occurred only for faces repeated with the same viewpoint, but not with a different viewpoint, confirming previous studies using faces only. By contrast, a region in right medial FG, adjacent to but nonoverlapping with the more lateral and face-selective FG, showed repetition effects for faces and to a lesser extent for other objects, regardless of changes in viewpoint or in retinal image-size. Category- and viewpoint-independent repetition effects were also found in bilateral LOC. Our results reveal a common neural substrate in bilateral LOC and right medial FG underlying view-invariant and category-independent recognition for multiple object identities, with only a relative preference for faces in medial FG but no selectivity in LO

FMRI and ERP investigations of body representations in the human lateral and ventral occipitotemporal cortex

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Human posterior parietal cortex mediates hand-specific planning

The processes underlying action planning are fundamental to adaptive behavior and can be influenced by recent motor experience. Here, we used a novel fMRI Repetition Suppression (RS) design to test the hypotheses that action planning unfolds more efficiently for successive actions made with the same hand. More efficient processing was predicted to correspond with both faster response times (RTs) to initiate actions and reduced fMRI activity levels � RS. Consistent with these predictions, we detected faster RTs for actions made with the same hand and accompanying fMRI-RS within bilateral posterior parietal cortex and right-lateralized parietal operculum. Within posterior parietal cortex, these RS effects were localized to intraparietal and superior parietal cortices. These same areas were more strongly activated for actions involving the contralateral hand. The findings provide compelling new evidence for the specification of action plans in hand-specific terms, and indicate that these processes are sensitive to recent motor history. Consistent with computational efficiency accounts of motor history effects, the findings are interpreted as evidence for comparatively more efficient processing underlying action planning when successive actions involve the same versus opposite hand

How the brain grasps tools: fMRI & motion-capture investigations

Humans’ ability to learn about and use tools is considered a defining feature of our species, with most related neuroimaging investigations involving proxy 2D picture viewing tasks. Using a novel tool grasping paradigm across three experiments, participants grasped 3D-printed tools (e.g., a knife) in ways that were considered to be typical (i.e., by the handle) or atypical (i.e., by the blade) for subsequent use. As a control, participants also performed grasps in corresponding directions on a series of 3D-printed non-tool objects, matched for properties including elongation and object size. Project 1 paired a powerful fMRI block-design with visual localiser Region of Interest (ROI) and searchlight Multivoxel Pattern Analysis (MVPA) approaches. Most remarkably, ROI MVPA revealed that hand-selective, but not anatomically overlapping tool-selective, areas of the left Lateral Occipital Temporal Cortex and Intraparietal Sulcus represented the typicality of tool grasping. Searchlight MVPA found similar evidence within left anterior temporal cortex as well as right parietal and temporal areas. Project 2 measured hand kinematics using motion-capture during a highly similar procedure, finding hallmark grip scaling effects despite the unnatural task demands. Further, slower movements were observed when grasping tools, relative to non-tools, with grip scaling also being poorer for atypical tool, compared to non-tool, grasping. Project 3 used a slow-event related fMRI design to investigate whether representations of typicality were detectable during motor planning, but MVPA was largely unsuccessful, presumably due to a lack of statistical power. Taken together, the representations of typicality identified within areas of the ventral and dorsal, but not ventro-dorsal, pathways have implications for specific predictions made by leading theories about the neural regions supporting human tool-use, including dual visual stream theory and the two-action systems model

Who is that? Brain networks and mechanisms for identifying individuals

Social animals can identify conspecifics by many forms of sensory input. However, whether the neuronal computations that support this ability to identify individuals rely on modality-independent convergence or involve ongoing synergistic interactions along the multiple sensory streams remains controversial. Direct neuronal measurements at relevant brain sites could address such questions, but this requires better bridging the work in humans and animal models. Here, we overview recent studies in nonhuman primates on voice and face identity-sensitive pathways and evaluate the correspondences to relevant findings in humans. This synthesis provides insights into converging sensory streams in the primate anterior temporal lobe (ATL) for identity processing. Furthermore, we advance a model and suggest how alternative neuronal mechanisms could be tested

Perception meets action: fMRI and behavioural investigations of human tool use

Tool use is essential and culturally universal to human life, common to hunter-gatherer and modern advanced societies alike. Although the neuroscience of simpler visuomotor behaviors like reaching and grasping have been studied extensively, relatively little is known about the brain mechanisms underlying learned tool use. With learned tool use, stored knowledge of object function and use supervene requirements for action programming based on physical object properties. Contemporary models of tool use based primarily on evidence from the study of brain damaged individuals implicate a set of specialized brain areas underlying the planning and control of learned actions with objects, distinct from areas devoted to more basic aspects of visuomotor control. The findings from the current thesis build on these existing theoretical models and provide new insights into the neural and behavioural mechanisms of learned tool use. In Project 1, I used fMRI to visualize brain activity in response to viewing tool use grasping. Grasping actions typical of how tools are normally grasped during use were found to preferentially activate occipitotemporal areas, including areas specialized for visual object recognition. The findings revealed sensitivity within this network to learned contextual associations tied to stored knowledge of tool-specific actions. The effects were seen to arise implicitly, in the absence of concurrent effects in visuomotor areas of parietofrontal cortex. These findings were taken to reflect the tuning of higher-order visual areas of occipitotemporal cortex to learned statistical regularities of the visual world, including the way in which tools are typically seen to be grasped and used. These areas are likely to represent an important source of inputs to visuomotor areas as to learned conceptual knowledge of tool use. In Project 2, behavioural priming and the kinematics of real tool use grasping was explored. Behavioural priming provides an index into the planning stages of actions. Participants grasped tools to either move them, grasp-to-move (GTM), or to demonstrate their common use, grasp-to-use (GTU), and grasping actions were preceded by a visual preview (prime) of either the same (congruent) or different (incongruent) tool as that which was then acted with. Behavioural priming was revealed as a reaction time advantage for congruent trial types, thought to reflect the triggering of learned use-based motor plans by the viewing of tools at prime events. The findings from two separate experiments revealed differential sensitivity to priming according to task and task setting. When GTU and GTM tasks were presented separately, priming was specific to the GTU task. In contrast, when GTU and GTM tasks were presented in the same block of trials, in a mixed task setting, priming was evident for both tasks. Together the findings indicate the importance of both task and task setting in shaping effects of action priming, likely driven by differences in the allocation of attentional resources. Differences in attention to particular object features, in this case tool identity, modulate affordances driven by those features which in turn determines priming. Beyond the physical properties of objects, knowledge and intention of use provide a mechanism for which affordances and the priming of actions may operate. Project 3 comprised a neuroimaging variant of the behavioural priming paradigm used in Project 2, with tools and tool use actions specially tailored for the fMRI environment. Preceding tool use with a visual preview of the tool to be used gave rise to reliable neural priming, measured as reduced BOLD activity. Neural priming of tool use was taken to reflect increased metabolic efficiency in the retrieval and implementation of stored tool use plans. To demonstrate specificity of priming for familiar tool use, a control task was used whereby actions with tools were determined not by tool identity but by arbitrarily learned associations with handle color. The findings revealed specificity for familiar tool-use priming in four distinct parietofrontal areas, including left inferior parietal cortex previously implicated in the storage of learned tool use plans. Specificity of priming for tool-action and not color-action associations provides compelling evidence for tool-use-experience-dependent plasticity within parietofrontal areas

Shared neural processes support semantic control and action understanding

Executive-semantic control and action understanding appear to recruit overlapping brain regions but existing evidence from neuroimaging meta-analyses and neuropsychology lacks spatial precision; we therefore manipulated difficulty and feature type (visual vs. action) in a single fMRI study. Harder judgements recruited an executive-semantic network encompassing medial and inferior frontal regions (including LIFG) and posterior temporal cortex (including pMTG). These regions partially overlapped with brain areas involved in action but not visual judgements. In LIFG, the peak responses to action and difficulty were spatially identical across participants, while these responses were overlapping yet spatially distinct in posterior temporal cortex. We propose that the co-activation of LIFG and pMTG allows the flexible retrieval of semantic information, appropriate to the current context; this might be necessary both for semantic control and understanding actions. Feature selection in difficult trials also recruited ventral occipital-temporal areas, not implicated in action understanding