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Institute Talks

"Exploring” Haptics: Human-Machine Interactive Applications from Mid-Air Laser Haptics to Sensorimotor Skill Learning

Talk
  • 25 February 2019 • 10:30 11:15
  • Hojin Lee
  • MPI-IS Stuttgart, Heisenbergstr. 3, Room 2P4

Haptic technologies in both kinesthetic and tactile aspects benefit a brand-new opportunity to recent human-machine interactive applications. In this talk, I, who believe in that one of the essential role of a researcher is pioneering new insights and knowledge, will present my previous research topics about haptic technologies and human-machine interactive applications in two branches: laser-based mid-air haptics and sensorimotor skill learning. For the former branch, I will introduce our approach named indirect laser radiation and its application. Indirect laser radiation utilizes a laser and a light-absorbing elastic medium to evoke a tapping-like tactile sensation. For the latter, I will introduce our data-driven approach for both modeling and learning of sensorimotor skills (especially, driving) with kinesthetic assistance and artificial neural networks; I call it human-like haptic assistance. To unify two different branches of my earlier studies for exploring the feasibility of the sensory channel named "touch", I will present a general research paradigm for human-machine interactive applications to which current haptic technologies can aim in future.

Organizers: Katherine J. Kuchenbecker

Virtual Reality Based Needle Insertion Simulation With Haptic Feedback: A Psychophysical Study

Talk
  • 25 February 2019 • 11:15 12:00
  • Ravali Gourishetti
  • MPI-IS Stuttgart, Heisenbergstr. 3, Room 2P4

Needle insertion is the most essential skill in medical care; training has to be imparted not only for physicians but also for nurses and paramedics. In most needle insertion procedures, haptic feedback from the needle is the main stimulus that novices are to be trained in. For better patient safety, the classical methods of training the haptic skills have to be replaced with simulators based on new robotic and graphics technologies. The main objective of this work is to develop analytical models of needle insertion (a special case of epidural anesthesia) including the biomechanical and psychophysical concepts that simulate the needle-tissue interaction forces in linear heterogeneous tissues and to validate the model with a series of experiments. The biomechanical and perception models were validated with experiments in two stages: with and without the human intervention. The second stage is the validation using the Turing test with two different experiments: 1) to observe the perceptual difference between the simulated and the physical phantom model, and 2) to verify the effectiveness of perceptual filter between the unfiltered and filtered model response. The results showed that the model could replicate the physical phantom tissues with good accuracy. This can be further extended to a non-linear heterogeneous model. The proposed needle/tissue interaction force models can be used more often in improving realism, performance and enabling future applications in needle simulators in heterogeneous tissue. Needle insertion training simulator was developed with the simulated models using Omni Phantom and clinical trials are conducted for the face validity and construct validity. The face validity results showed that the degree of realism of virtual environments and instruments had the overall lowest mean score and ease of usage and training in hand – eye coordination had the highest mean score. The construct validity results showed that the simulator was able to successfully differentiate force and psychomotor signatures of anesthesiologists with experiences less than 5 years and more than 5 years. For the performance index of the trainees, a novel measure, Just Controllable Difference (JCD) was proposed and a preliminary study on JCD measure is explored using two experiments for the novice. A preliminary study on the use of clinical training simulations, especially needle insertion procedure in virtual environments is emphasized on two objectives: Firstly, measures of force JND with the three fingers and secondly, comparison of these measures in Non-Immersive Virtual Reality (NIVR) to that of the Immersive Virtual Reality (IVR) using psychophysical study with the Force Matching task, Constant Stimuli method, and Isometric Force Probing stimuli. The results showed a better force JND in the IVR compared to that of the NIVR. Also, a simple state observer model was proposed to explain the improvement of force JND in the IVR. This study would quantitatively reinforce the use of the IVR for the design of various medical simulators.

Organizers: Katherine J. Kuchenbecker

Design of functional polymers for biomedical applications

Talk
  • 27 February 2019 • 14:00 15:00
  • Dr. Salvador Borrós Gómez
  • Stuttgart 2P4

Functional polymers can be easily tailored for their interaction with living organismes. In our Group, we have worked during the last 15 years in the development of this kind of polymeric materials with different funcionalities, high biocompatibility and in different forms. In this talk, we will describe the synthesis of thermosensitive thin films that can be used to prevent biofilm formation in medical devices, the preparation of biodegradable polymers specially designed for vectors for gene transfection and a new familliy of zwitterionic polymers that are able to cross intestine mucouse for oral delivery applications. The relationship between structure-functionality- applications will be discussed for every example.

Organizers: Metin Sitti

A new path to understanding biological/human vision: theory and experiments

IS Colloquium
  • 11 March 2019 • 14:00 15:00
  • Zhaoping Li
  • MPI-IS lecture hall (N0.002)

Since Hubel and Wiesel's seminal findings in the primary visual cortex (V1) more than 50 years ago, progress in vision science has been very limited along previous frameworks and schools of thoughts on understanding vision. Have we been asking the right questions? I will show observations motivating the new path. First, a drastic information bottleneck forces the brain to process only a tiny fraction of the massive visual input information; this selection is called the attentional selection, how to select this tiny fraction is critical. Second, a large body of evidence has been accumulating to suggest that the primary visual cortex (V1) is where this selection starts, suggesting that the visual cortical areas along the visual pathway beyond V1 must be investigated in light of this selection in V1. Placing attentional selection as the center stage, a new path to understanding vision is proposed (articulated in my book "Understanding vision: theory, models, and data", Oxford University Press 2014). I will show a first example of using this new path, which aims to ask new questions and make fresh progresses. I will relate our insights to artificial vision systems to discuss issues like top-down feedbacks in hierachical processing, analysis-by-synthesis, and image understanding.

Organizers: Timo Bolkart Aamir Ahmad

Improving the Gaussian Mechanism for Differential Privacy

IS Colloquium
  • 27 June 2018 • 14:15 15:15
  • Borja de Balle Pigem
  • MPI IS lecture hall (N0.002)

The Gaussian mechanism is an essential building block used in multitude of differentially private data analysis algorithms. In this talk I will revisit the classical analysis of the Gaussian mechanism and show it has several important limitations. For example, our analysis reveals that the variance formula for the original mechanism is far from tight in the high privacy regime and that it cannot be extended to the low privacy regime. We address these limitations by developing a new Gaussian mechanism whose variance is optimally calibrated by solving an equation involving the Gaussian cumulative density function. Our analysis side-steps the use of tail bounds approximations and relies on a novel characterisation of differential privacy that might be of independent interest. We numerically show that analytical calibration removes at least a third of the variance of the noise compared to the classical Gaussian mechanism. We also propose to equip the Gaussian mechanism with a post-processing step based on adaptive denoising estimators by leveraging that the variance of the perturbation is known. Experiments with synthetic and real data show that this denoising step yields dramatic accuracy improvements in the high-dimensional regime. Based on joint work with Y.-X. Wang to appear at ICML 2018. Pre-print: https://arxiv.org/abs/1805.06530

Organizers: Michel Besserve Isabel Valera


  • Daniel Häufle
  • 3P2, MPI IS stuttgart

Organizers: Alexander Sproewitz


Haptic Engineering and Science at Multiple Scales

IS Colloquium
  • 20 June 2018 • 11:00 12:00
  • Yon Visell, PhD
  • MPI-IS Stuttgart, Heisenbergstr. 3, Room 2P4

I will describe recent research in my lab on haptics and robotics. It has been a longstanding challenge to realize engineering systems that can match the amazing perceptual and motor feats of biological systems for touch, including the human hand. Some of the difficulties of meeting this objective can be traced to our limited understanding of the mechanics, and to the high dimensionality of the signals, and to the multiple length and time scales - physical regimes - involved. An additional source of richness and complication arises from the sensitive dependence of what we feel on what we do, i.e. on the tight coupling between touch-elicited mechanical signals, object contacts, and actions. I will describe research in my lab that has aimed at addressing these challenges, and will explain how the results are guiding the development of new technologies for haptics, wearable computing, and robotics.

Organizers: Katherine J. Kuchenbecker


Less-artificial intelligence

Talk
  • 18 June 2018 • 15:00 16:00
  • Prof. Dr. Matthias Bethge
  • MPI-IS Stuttgart - 2R04


  • Karl Rohe
  • MPI IS Lecture Hall (N0.002)

This paper uses the relationship between graph conductance and spectral clustering to study (i) the failures of spectral clustering and (ii) the benefits of regularization. The explanation is simple. Sparse and stochastic graphs create a lot of small trees that are connected to the core of the graph by only one edge. Graph conductance is sensitive to these noisy "dangling sets." Spectral clustering inherits this sensitivity. The second part of the paper starts from a previously proposed form of regularized spectral clustering and shows that it is related to the graph conductance on a "regularized graph." We call the conductance on the regularized graph CoreCut. Based upon previous arguments that relate graph conductance to spectral clustering (e.g. Cheeger inequality), minimizing CoreCut relaxes to regularized spectral clustering. Simple inspection of CoreCut reveals why it is less sensitive to small cuts in the graph. Together, these results show that unbalanced partitions from spectral clustering can be understood as overfitting to noise in the periphery of a sparse and stochastic graph. Regularization fixes this overfitting. In addition to this statistical benefit, these results also demonstrate how regularization can improve the computational speed of spectral clustering. We provide simulations and data examples to illustrate these results.

Organizers: Damien Garreau


  • Adrián Javaloy
  • S2 seminar room

The problem of text normalization is simple to understand: transform a given arbitrary text into its spoken form. In the context of text-to-speech systems – that we will focus on – this can be exemplified by turning the text “$200” into “two hundred dollars”. Lately, the interest of solving this problem with deep learning techniques has raised since it is a highly context-dependent problem that is still being solved by ad-hoc solutions. So much so that Google even started a contest in the web Kaggle to solve this problem. In this talk we will see how this problem has been approached as part of a Master thesis. Namely, the problem is tackled as if it were an automatic translation problem from English to normalized English, and so the architecture proposed is a neural machine translation architecture with the addition of traditional attention mechanisms. This network is typically composed of an encoder and a decoder, where both of them are multi-layer LSTM networks. As part of this work, and with the aim of proving the feasibility of convolutional neural networks in natural-language processing problems, we propose and compare different architectures for the encoder based on convolutional networks. In particular, we propose a new architecture called Causal Feature Extractor which proves to be a great encoder as well as an attention-friendly architecture.

Organizers: Philipp Hennig


  • Prof. Andrew Blake
  • Ground Floor Seminar Room N0.002

Organizers: Ahmed Osman


Learning Representations for Hyperparameter Transfer Learning

IS Colloquium
  • 11 June 2018 • 11:15 12:15
  • Cédric Archambeau
  • MPI IS Lecture Hall (N0.002)

Bayesian optimization (BO) is a model-based approach for gradient-free black-box function optimization, such as hyperparameter optimization. Typically, BO relies on conventional Gaussian process regression, whose algorithmic complexity is cubic in the number of evaluations. As a result, Gaussian process-based BO cannot leverage large numbers of past function evaluations, for example, to warm-start related BO runs. After a brief intro to BO and an overview of several use cases at Amazon, I will discuss a multi-task adaptive Bayesian linear regression model, whose computational complexity is attractive (linear) in the number of function evaluations and able to leverage information of related black-box functions through a shared deep neural net. Experimental results show that the neural net learns a representation suitable for warm-starting related BO runs and that they can be accelerated when the target black-box function (e.g., validation loss) is learned together with other related signals (e.g., training loss). The proposed method was found to be at least one order of magnitude faster than competing neural network-based methods recently published in the literature. This is joint work with Valerio Perrone, Rodolphe Jenatton, and Matthias Seeger.

Organizers: Isabel Valera


  • Prof. Martin Spindler
  • MPI IS Lecture Hall (N0.002)

In this talk first an introduction to the double machine learning framework is given. This allows inference on parameters in high-dimensional settings. Then, two applications are given, namely transformation models and Gaussian graphical models in high-dimensional settings. Both kind of models are widely used by practitioners. As high-dimensional data sets become more and more available, it is important to allow situations where the number of parameters is large compared to the sample size.


  • Prof. Martin Spindler
  • MPI IS Lecture Hall (N0.002)

In this talk first an introduction to the double machine learning framework is given. This allows inference on parameters in high-dimensional settings. Then, two applications are given, namely transformation models and Gaussian graphical models in high-dimensional settings. Both kind of models are widely used by practitioners. As high-dimensional data sets become more and more available, it is important to allow situations where the number of parameters is large compared to the sample size.

Organizers: Philipp Geiger