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

Representational structure of fMRI/EEG responses to dynamic facial expressions

Face perception provides an excellent example of how the brain processes nuanced visual differences and trans-forms them into behaviourally useful representations of identities and emotional expressions. While a body of literature has looked into the spatial and temporal neural processing of facial expressions, few studies have used a dimensionally varying set of stimuli containing subtle perceptual changes. In the current study, we used 48 short videos varying dimensionally in their intensity and category (happy, angry, surprised) of expression. We measured both fMRI and EEG responses to these video clips and compared the neural response patterns to the predictions of models based on image features and models derived from behavioural ratings of the stimuli. In fMRI, the inferior frontal gyrus face area (IFG-FA) carried information related only to the intensity of the expres-sion, independent of image-based models. The superior temporal sulcus (STS), inferior temporal (IT) and lateral occipital (LO) areas contained information about both expression category and intensity. In the EEG, the coding of expression category and low-level image features were most pronounced at around 400 ms. The expression intensity model did not, however, correlate significantly at any EEG timepoint. Our results show a specific role for IFG-FA in the coding of expressions and suggest that it contains image and category invariant representations of expression intensity.Peer reviewe

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

​The International Symposium on Hearing is a prestigious, triennial gathering where world-class scientists present and discuss the most recent advances in the field of human and animal hearing research. The 2015 edition will particularly focus on integrative approaches linking physiological, psychophysical and cognitive aspects of normal and impaired hearing. Like previous editions, the proceedings will contain about 50 chapters ranging from basic to applied research, and of interest to neuroscientists, psychologists, audiologists, engineers, otolaryngologists, and artificial intelligence researchers.

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

otorhinolaryngology; neurosciences; hearin

Distributed networks for auditory memory differentially contribute to recall precision

Re-directing attention to objects in working memory can enhance their representational fidelity. However, how this attentional enhancement of memory representations is implemented across distinct, sensory and cognitive-control brain network is unspecified. The present fMRI experiment leverages psychophysical modelling and multivariate auditory-pattern decoding as behavioral and neural proxies of mnemonic fidelity. Listeners performed an auditory syllable pitch-discrimination task and received retro-active cues to selectively attend to a to-be-probed syllable in memory. Accompanied by increased neural activation in fronto-parietal and cingulo-opercular networks, valid retro-cues yielded faster and more perceptually sensitive responses in recalling acoustic detail of memorized syllables. Information about the cued auditory object was decodable from hemodynamic response patterns in superior temporal sulcus (STS), fronto-parietal, and sensorimotor regions. However, among these regions retaining auditory memory objects, neural fidelity in the left STS and its enhancement through attention-to-memory best predicted individuals’ gain in auditory memory recall precision. Our results demonstrate how functionally discrete brain regions differentially contribute to the attentional enhancement of memory representations