Gemma A. Calvert

Bio: Gemma A. Calvert is an academic researcher from Nanyang Technological University. The author has contributed to research in topics: Functional magnetic resonance imaging & Multisensory integration. The author has an hindex of 33, co-authored 70 publications receiving 9932 citations. Previous affiliations of Gemma A. Calvert include King's College London & John Radcliffe Hospital.

The Handbook of Multisensory Processing

Abstract: This landmark reference work brings together for the first time in one volume the most recent research from different areas of the emerging field of multisensory integration. After many years of using a modality-specific "sense-by-sense" approach, researchers across different disciplines in neuroscience and psychology now recognize that perception is fundamentally a multisensory experience. To understand how the brain synthesizes information from the different senses, we must study not only how information from each sensory modality is decoded but also how this information interacts with the sensory processing taking place within other sensory channels. The findings cited in The Handbook of Multisensory Processes suggest that there are broad underlying principles that govern this interaction, regardless of the specific senses involved.The book is organized thematically into eight sections; each of the 55 chapters presents a state-of-the-art review of its topic by leading researchers in the field. The key themes addressed include multisensory contributions to perception in humans; whether the sensory integration involved in speech perception is fundamentally different from other kinds of multisensory integration; multisensory processing in the midbrain and cortex in model species, including rat, cat, and monkey; behavioral consequences of multisensory integration; modern neuroimaging techniques, including EEG, PET, and fMRI, now being used to reveal the many sites of multisensory processing in the brain; multisensory processes that require postnatal sensory experience to emerge, with examples from multiple species; brain specialization and possible equivalence of brain regions; and clinical studies of such breakdowns of normal sensory integration as brain damage and synesthesia.

Crossmodal Processing in the Human Brain: Insights from Functional Neuroimaging Studies

Abstract: Modern brain imaging techniques have now made it possible to study the neural sites and mechanisms underlying crossmodal processing in the human brain. This paper reviews positron emission tomography, functional magnetic resonance imaging (fMRI), event-related potential and magnetoencephalographic studies of crossmodal matching, the crossmodal integration of content and spatial information, and crossmodal learning. These investigations are beginning to produce some consistent findings regarding the neuronal networks involved in these distinct crossmodal operations. Increasingly, specific roles are being defined for the superior temporal sulcus, the inferior parietal sulcus, regions of frontal cortex, the insula cortex and claustrum. The precise network of brain areas implicated in any one study, however, seems to be heavily dependent on the experimental paradigms used, the nature of the information being combined and the particular combination of modalities under investigation. The different analytic strategies adopted by different groups may also be a significant factor contributing to the variability in findings. In this paper, we demonstrate the impact of computing intersections, conjunctions and interaction effects on the identification of audiovisual integration sites using existing fMRI data from our own laboratory. This exercise highlights the potential value of using statistical interaction effects to model electrophysiological responses to crossmodal stimuli in order to identify possible sites of multisensory integration in the human brain.

Activation of Auditory Cortex During Silent Lipreading

Abstract: Watching a speaker's lips during face-to-face conversation (lipreading) markedly improves speech perception, particularly in noisy conditions. With functional magnetic resonance imaging it was found that these linguistic visual cues are sufficient to activate auditory cortex in normal hearing individuals in the absence of auditory speech sounds. Two further experiments suggest that these auditory cortical areas are not engaged when an individual is viewing nonlinguistic facial movements but appear to be activated by silent meaningless speechlike movements (pseudospeech). This supports psycholinguistic evidence that seen speech influences the perception of heard speech at a prelexical stage.

Dynamic mapping of human cortical development during childhood through early adulthood

Abstract: We report the dynamic anatomical sequence of human cortical gray matter development between the age of 4–21 years using quantitative four-dimensional maps and time-lapse sequences. Thirteen healthy children for whom anatomic brain MRI scans were obtained every 2 years, for 8–10 years, were studied. By using models of the cortical surface and sulcal landmarks and a statistical model for gray matter density, human cortical development could be visualized across the age range in a spatiotemporally detailed time-lapse sequence. The resulting time-lapse “movies” reveal that (i) higher-order association cortices mature only after lower-order somatosensory and visual cortices, the functions of which they integrate, are developed, and (ii) phylogenetically older brain areas mature earlier than newer ones. Direct comparison with normal cortical development may help understanding of some neurodevelopmental disorders such as childhood-onset schizophrenia or autism.

Automatically Parcellating the Human Cerebral Cortex

Abstract: We present a technique for automatically assigning a neuroanatomical label to each location on a cortical surface model based on probabilistic information estimated from a manually labeled training set. This procedure incorporates both geometric information derived from the cortical model, and neuroanatomical convention, as found in the training set. The result is a complete labeling of cortical sulci and gyri. Examples are given from two different training sets generated using different neuroanatomical conventions, illustrating the flexibility of the algorithm. The technique is shown to be comparable in accuracy to manual labeling.

The neural basis of human error processing: Reinforcement learning, dopamine, and the error-related negativity.

Abstract: The authors present a unified account of 2 neural systems concerned with the development and expression of adaptive behaviors: a mesencephalic dopamine system for reinforcement learning and a “generic” error-processing system associated with the anterior cingulate cortex The existence of the error-processing system has been inferred from the error-related negativity (ERN), a component of the event-related brain potential elicited when human participants commit errors in reaction-time tasks The authors propose that the ERN is generated when a negative reinforcement learning signal is conveyed to the anterior cingulate cortex via the mesencephalic dopamine system and that this signal is used by the anterior cingulate cortex to modify performance on the task at hand They provide support for this proposal using both computational modeling and psychophysiological experimentation