Patrick De Mazière

A Distinct Representation of Three-Dimensional Shape in Macaque Anterior Intraparietal Area: Fast, Metric, and Coarse

Differences in the horizontal positions of retinal images—binocular disparity—provide important cues for three-dimensional object recognition and manipulation. We investigated the neural coding of three-dimensional shape defined by disparity in anterior intraparietal (AIP) area. Robust selectivity for disparity-defined slanted and curved surfaces was observed in a high proportion of AIP neurons, emerging at relatively short latencies. The large majority of AIP neurons preserved their three-dimensional shape preference over different positions in depth, a hallmark of higher-order disparity selectivity. Yet both stimulus type (concave–convex) and position in depth could be reliably decoded from the AIP responses. The neural coding of three-dimensional shape was based on first-order (slanted surfaces) and second-order (curved surfaces) disparity selectivity. Many AIP neurons tolerated the presence of disparity discontinuities in the stimulus, but the population of AIP neurons provided reliable information on the degree of curvedness of the stimulus. Finally, AIP neurons preserved their three-dimensional shape preference over different positions in the frontoparallel plane. Thus, AIP neurons extract or have access to three-dimensional object information defined by binocular disparity, consistent with previous functional magnetic resonance imaging data. Unlike the known representation of three-dimensional shape in inferior temporal cortex, the neural representation in AIP appears to emphasize object parameters required for the planning of grasping movements.

Distinct Mechanisms for Coding of Visual Actions in Macaque Temporal Cortex

Temporal cortical neurons are known to respond to visual dynamic-action displays. Many human psychophysical and functional imaging studies examining biological motion perception have used treadmill walking, in contrast to previous macaque single-cell studies. We assessed the coding of locomotion in rhesus monkey (Macaca mulatta) temporal cortex using movies of stationary walkers, varying both form and motion (i.e., different facing directions) or varying only the frame sequence (i.e., forward vs backward walking). The majority of superior temporal sulcus and inferior temporal neurons were selective for facing direction, whereas a minority distinguished forward from backward walking. Support vector machines using the temporal cortical population responses as input classified facing direction well, but forward and backward walking less so. Classification performance for the latter improved markedly when the within-action response modulation was considered, reflecting differences in momentary body poses within the locomotion sequences. Responses to static pose presentations predicted the responses during the course of the action. Analyses of the responses to walking sequences wherein the start frame was varied across trials showed that some neurons also carried a snapshot sequence signal. Such sequence information was present in neurons that responded to static snapshot presentations and in neurons that required motion. Our data suggest that actions are analyzed by temporal cortical neurons using distinct mechanisms. Most neurons predominantly signal momentary pose. In addition, temporal cortical neurons, including those responding to static pose, are sensitive to pose sequence, which can contribute to the signaling of learned action sequences.

Coding of images of materials by macaque inferior temporal cortical neurons.

Objects vary not only in their shape but also in the material from which they are made. Knowledge of the material properties can contribute to object recognition as well as indicate properties of the object (e.g. ripeness of a fruit). We examined the coding of images of materials by single neurons of the macaque inferior temporal (IT) cortex, an area known to support object recognition and categorization. Stimuli were images of 12 real materials that were illuminated from three different directions. The material textures appeared within five different outline shapes. The majority of responsive IT neurons responded selectively to the material textures, and this selectivity was largely independent of their shape selectivity. The responses of the large majority of neurons were strongly affected by illumination direction. Despite the generally weak illumination‐direction invariance of the responses, Support Vector Machines that used the neural responses as input were able to classify the materials across illumination direction better than by chance. A comparison between the responses to the original images and those to images with a random spectral phase, but matched power spectrum, indicated that the material texture selectivity did not depend merely on differences in the power spectrum but required phase information.

Fine-grained stimulus representations in body selective areas of human occipito-temporal cortex.

Neurophysiological and functional imaging studies have investigated the representation of animate and inanimate stimulus classes in monkey inferior temporal (IT) and human occipito-temporal cortex (OTC). These studies proposed a distributed representation of stimulus categories across IT and OTC and at the same time highlighted category specific modules for the processing of bodies, faces and objects. Here, we investigated whether the stimulus representation within the extrastriate (EBA) and the fusiform (FBA) body areas differed from the representation across OTC. To address this question, we performed an event-related fMRI experiment, evaluating the pattern of activation elicited by 200 individual stimuli that had already been extensively tested in our earlier monkey imaging and single cell studies (Popivanov et al., 2012, 2014). The set contained achromatic images of headless monkey and human bodies, two sets of man-made objects, monkey and human faces, four-legged mammals, birds, fruits, and sculptures. The fMRI response patterns within EBA and FBA primarily distinguished bodies from non-body stimuli, with subtle differences between the areas. However, despite responding on average stronger to bodies than to other categories, classification performance for preferred and non-preferred categories was comparable. OTC primarily distinguished animate from inanimate stimuli. However, cluster analysis revealed a much more fine-grained representation with several homogeneous clusters consisting entirely of stimuli of individual categories. Overall, our data suggest that category representation varies with location within OTC. Nevertheless, body modules contain information to discriminate also non-preferred stimuli and show an increasing specificity in a posterior to anterior gradient.

A clustering study of a 7000 EU document inventory using MDS and SOM

In this article, we discuss a number of methods and tools to cluster a 7000 document inventory in order to evaluate the impact of EU funded research in social sciences and humanities on EU policies. The inventory, which is not publicly available, but provided to us by the European Union (EU) in the framework of an EU project, could be divided into three main categories: research documents, influential policy documents, and policy documents. To represent the results in a way that non-experts could make use of it, we explored and compared two visualisation techniques, multi-dimensional scaling (MDS) and the self-organising map (SOM), and one of the latters derivatives, the U-matrix. Contrary to most other approaches, which perform text analyses only on document titles and abstracts, we performed a full text analysis on more than 300,000 pages in total. Due to the inability of many software suites to handle text mining problems of this size, we developed our own analysis platform. We show that the combination of a U-matrix and an MDS map, which is rarely performed in the domain of text mining, reveals information that would go unnoticed otherwise. Furthermore, we show that the combination of a database, to store the data and the (intermediate) results, and a webserver, to visualise the results, offers a powerful platform to analyse the data and share the results with all participants/collaborators involved in a data- and computation intensive EU-project, thereby guaranteeing both data- and result consistency.

Brain-computer interface research at Katholieke Universiteit Leuven

We present an overview of our Brain-computer interface (BCI) research, invasive as well as non-invasive, during the past four years. The invasive BCIs are based on local field-and action potentials recorded with microelectrode arrays implanted in the visual cortex of the macaque monkey. The non-invasive BCIs are based on electroencephalogram (EEG) recorded from a human subjects scalp. Several EEG paradigms were used to enable the subject to type text or to select icons on a computer screen, without having to rely on ones fingers, gestures, or any other form of motor activity: the P300 event-related potential, the steady-state visual evoked potential, and the error related potential. We report on the status of our EEG BCI tests on healthy subjects as well as patients with severe communication disabilities, and our demonstrations to a broad audience to raise the public awareness of BCI.

Shedding light on an unknown reality in solid organ transplant patients’ self-management: A contextual inquiry study

Traditional quantitative and qualitative research methods inadequately capture the complexity of patients’ daily self‐management. Contextual inquiry methodology, using home visits, allows a more in‐depth understanding of how patients integrate immunosuppressive medication intake, physical activity, and healthy eating in their daily lives, and which difficulties they experience when doing so. This mixed‐method study comprised 2 home visits in 19 purposively selected adult heart, lung, liver, and kidney transplant patients, asking them to demonstrate how they implement the aforementioned health behaviors. Meanwhile, conversations were audio‐taped and photographs were taken. Audio‐visual materials were coded using directed content analysis. Difficulties and supportive strategies were identified via inductive thematic analysis. We learned that few patients understood what “sufficiently active” means. Physical discomforts and poor motivation created variation across activity levels observed. Health benefits of dietary guidelines were insufficiently understood, and their implementation into everyday life considered difficult. Many underestimated the strictness of immunosuppressive medication intake, and instructions on handling late doses were unclear. Interruptions in routine and busyness contributed to nonadherence. We also learned that professionals often recommend supportive strategies, which patients not always like or need. This contextual inquiry study revealed unique insights, providing a basis for patient‐tailored self‐management interventions.

Inter-document reference detection as an alternative to full text semantic analysis in document clustering

We discuss here the search for inter-document references as an alternative to the grouping of document inventories based on a full text semantic analysis. The used document inventory, which is not publicly available, was provided to us by the European Union (EU) in the framework of an EU project, the aim of which was to analyse, classify, and visualise EU funded research in social sciences and humanities in EU framework programmes FP5 and FP6. This project, called the SSH project for short, was aimed at the evaluation of the contributions of research to the development of EU policies. For the semantic based grouping, we start from a Multi-Dimensional Scaling analysis of the document vectors, which is the result of a prior semantic analysis. As an alternative to a semantic analysis, we searched for inter-document references or direct references. Direct references are defined as terms that explicitly refer to other documents present in the inventory. We show that the grouping based on references is largely similar to the one based on semantics, but with considerably less computational efforts. In addition, the non-expert can make better use of the results, since the references are displayed as graphical webpages with hyperlinks pointing to both the referenced and the referencing document(s), and the reason of linkage. Finally, we show that the combination of a database, to store the data and the (intermediate) results, and a webserver, to visualise the results, offers a powerful platform to analyse the document inventory and to share the results with all participants/collaborators involved in a data- and computation intensive EU-project, thereby guaranteeing both data- and result-consistency.