63 research outputs found
Biologically Inspired Dynamic Textures for Probing Motion Perception
Perception is often described as a predictive process based on an optimal
inference with respect to a generative model. We study here the principled
construction of a generative model specifically crafted to probe motion
perception. In that context, we first provide an axiomatic, biologically-driven
derivation of the model. This model synthesizes random dynamic textures which
are defined by stationary Gaussian distributions obtained by the random
aggregation of warped patterns. Importantly, we show that this model can
equivalently be described as a stochastic partial differential equation. Using
this characterization of motion in images, it allows us to recast motion-energy
models into a principled Bayesian inference framework. Finally, we apply these
textures in order to psychophysically probe speed perception in humans. In this
framework, while the likelihood is derived from the generative model, the prior
is estimated from the observed results and accounts for the perceptual bias in
a principled fashion.Comment: Twenty-ninth Annual Conference on Neural Information Processing
Systems (NIPS), Dec 2015, Montreal, Canad
Perceptual Measurements, Distances and Metrics
Perception is often viewed as a process that transforms physical variables,
external to an observer, into internal psychological variables. Such a process
can be modeled by a function coined perceptual scale. The perceptual scale can
be deduced from psychophysical measurements that consist in comparing the
relative differences between stimuli (i.e. difference scaling experiments).
However, this approach is often overlooked by the modeling and experimentation
communities. Here, we demonstrate the value of measuring the perceptual scale
of classical (spatial frequency, orientation) and less classical physical
variables (interpolation between textures) by embedding it in recent
probabilistic modeling of perception. First, we show that the assumption that
an observer has an internal representation of univariate parameters such as
spatial frequency or orientation while stimuli are high-dimensional does not
lead to contradictory predictions when following the theoretical framework.
Second, we show that the measured perceptual scale corresponds to the
transduction function hypothesized in this framework. In particular, we
demonstrate that it is related to the Fisher information of the generative
model that underlies perception and we test the predictions given by the
generative model of different stimuli in a set a of difference scaling
experiments. Our main conclusion is that the perceptual scale is mostly driven
by the stimulus power spectrum. Finally, we propose that this measure of
perceptual scale is a way to push further the notion of perceptual distances by
estimating the perceptual geometry of images i.e. the path between images
instead of simply the distance between those.Comment: 15 pages, 6 figures, 5 appendi
Measuring uncertainty in human visual segmentation
Segmenting visual stimuli into distinct groups of features and visual objects
is central to visual function. Classical psychophysical methods have helped
uncover many rules of human perceptual segmentation, and recent progress in
machine learning has produced successful algorithms. Yet, the computational
logic of human segmentation remains unclear, partially because we lack
well-controlled paradigms to measure perceptual segmentation maps and compare
models quantitatively. Here we propose a new, integrated approach: given an
image, we measure multiple pixel-based same--different judgments and perform
model--based reconstruction of the underlying segmentation map. The
reconstruction is robust to several experimental manipulations and captures the
variability of individual participants. We demonstrate the validity of the
approach on human segmentation of natural images and composite textures. We
show that image uncertainty affects measured human variability, and it
influences how participants weigh different visual features. Because any
putative segmentation algorithm can be inserted to perform the reconstruction,
our paradigm affords quantitative tests of theories of perception as well as
new benchmarks for segmentation algorithms.Comment: 27 pages, 9 figures, 4 appendix, 3 figures in appendi
Probabilistic reachability and control synthesis for stochastic switched systems using the tamed Euler method
In this paper, we explain how, under the one-sided Lipschitz (OSL) hypothesis, one can find a mean square error bound for a variant of the Euler-Maruyama approximation method for stochastic switched systems. Subsequently, we explain how this bound can be used to control a stochastic switched system in order to make it reach a target zone with guaranteed minimum probability. The method is illustrated on several examples from the literature
Effect of different intravenous iron preparations on lymphocyte intracellular reactive oxygen species generation and subpopulation survival
<p>Abstract</p> <p>Background</p> <p>Infections in hemodialysis (HD) patients lead to high morbidity and mortality rates and are associated with early cardiovascular mortality, possibly related to chronic inflammation. Intravenous (IV) iron is widely administered to HD patients and has been associated with increased oxidative stress and dysfunctional cellular immunity. The purpose of this study was to examine the effect of three commercially available IV iron preparations on intracellular reactive oxygen species generation and lymphocyte subpopulation survival.</p> <p>Methods</p> <p>Peripheral blood mononuclear cells (PBMC) were isolated from healthy donor buffy coat. PBMC were cultured and incubated with 100 μg/mL of sodium ferric gluconate (SFG), iron sucrose (IS) or iron dextran (ID) for 24 hours. Cells were then probed for reactive oxygen species (ROS) with dichlorofluorescein-diacetate. In separate studies, isolated PBMCs were incubated with the 25, 50 or 100 μg/mL iron concentrations for 72 hours and then stained with fluorescein conjugated monoclonal antibodies for lymphocyte subpopulation identification. Untreated PBMCs at 24 hours and 72 hours served as controls for each experiment.</p> <p>Results</p> <p>All three IV iron preparations induced time dependent increases in intracellular ROS with SFG and IS having a greater maximal effect than ID. The CD4+ lymphocytes were most affected by IV iron exposure, with statistically significant reduction in survival after incubation with all three doses (10, 25 and 100 μg/mL) of SFG, IS and ID.</p> <p>Conclusion</p> <p>These data indicate IV iron products induce differential deleterious effects on CD4+ and CD16+ human lymphocytes cell populations that may be mediated by intracellular reactive oxygen species generation. Further studies are warranted to determine the potential clinical relevance of these findings.</p
Cursive Eye-Writing With Smooth-Pursuit Eye-Movement Is Possible in Subjects With Amyotrophic Lateral Sclerosis
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder causing a progressive motor weakness of all voluntary muscles, whose progression challenges communication modalities such as handwriting or speech. The current study investigated whether ALS subjects can use Eye-On-Line (EOL), a novel eye-operated communication device allowing, after training, to voluntarily control smooth-pursuit eye-movements (SPEM) so as to eye-write in cursive. To that aim, ALS participants (n = 12) with preserved eye-movements but impaired handwriting were trained during six on-site visits. The primary outcome of the study was the recognition of eye-written digits (0–9) from ALS and healthy control subjects by naïve “readers.” Changes in oculomotor performance and the safety of EOL were also evaluated. At the end of the program, 69.4% of the eye-written digits from 11 ALS subjects were recognized by naïve readers, similar to the 67.3% found for eye-written digits from controls participants, with however, large inter-individual differences in both groups of “writers.” Training with EOL was associated with a transient fatigue leading one ALS subject to drop out the study at the fifth visit. Otherwise, itching eyes was the most common adverse event (3 subjects). This study shows that, despite the impact of ALS on the motor system, most ALS participants could improve their mastering of eye-movements, so as to produce recognizable eye-written digits, although the eye-traces sometimes needed smoothing to ease digit legibility from both ALS subjects and control participants. The capability to endogenously and voluntarily generate eye-traces using EOL brings a novel way to communicate for disabled individuals, allowing creative personal and emotional expression
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