Abhranil Das

University of Texas at Austin | UT · Center for Theoretical and Computational Neuroscience

Understanding the mechanisms of neural computation and learning will require knowledge of the underlying circuitry. Because it is difficult to directly measure the wiring diagrams of neural circuits, there has long been an interest in estimating them algorithmically from multicell activity recordings. We show that even sophisticated methods, applie...

Univariate and multivariate normal probability distributions are widely used when modeling decisions under uncertainty. Computing the performance of such models requires integrating these distributions over specific domains, which can vary widely across models. Besides some special cases where these integrals are easy to calculate, there exists no...

Camouflage is an amazing feat of evolution, but also impressive is the ability of biological visual systems to detect them. They are the result of an evolutionary arms race that exposes many detection strategies and their limits. In this thesis, we investigate the principles of human detection of maximally-camouflaged objects, i.e. whose texture ex...

Psychedelics are natural or synthetic compounds, some with long histories of religious and cultural practice, which can induce remarkable changes in the human consciousness. After decades of suppression, the use and research of psychedelics are witnessing a new renaissance. At our new psychedelics research and therapy center, we are studying if cer...

Human psychophysics experiments, and Bayesian and convolutional network models of texture-discrimination.

We present several exact and approximate mathematical methods and open-source software to compute the cdf, pdf and inverse cdf of the generalized chi-square distribution. Some methods are geared for speed, while others are designed to be accurate far into the tails, using which we can also measure large values of the discriminability index $d'$ bet...

Psychedelics are natural or synthetic compounds, some with long histories of religious and cultural practice, which can induce remarkable changes in the human consciousness. After decades of suppression, the use and research of psychedelics are witnessing a new renaissance. At our new psychedelics research and therapy center, we are studying if cer...

Maximally camouflaged animals mimic the luminance, contrast, colour and texture of their background, so that the only cue left usable for detection is the edge. This is one of the hardest cases of visual detection, so studying this reveals many of our detection strategies and their limits. We conduct psychophysical experiments where humans detect a...

Maximally camouflaged animals mimic the luminance, contrast, colour and texture of their background, so that the only cue left usable for detection is the edge. This is one of the hardest cases of visual detection, so studying this reveals many of our detection strategies and their limits. We conduct psychophysical experiments where humans detect a...

Ways to make your code, paper and knowledge more accessible and visible.

When vertical columns of water are connected, the water reaches the same level in each column. This is traditionally explained using properties and laws of fluid pressure. In an unusual approach here, we ignore the idea of pressure, and instead bring together mathematical results from calculus, statistics, number theory and logic to derive the same...

Camouflage is an impressive feat of biology in which an animal’s surface evolves to match the reflectance and texture of the backgrounds against which it typically appears. Equally impressive is the ability of visual systems to detect such camouflage. We present a principled theory of camouflage detection based on task-relevant cues and biologicall...

Univariate and multivariate normal probability distributions are widely used when modeling decisions under uncertainty. Computing the performance of such models requires integrating these distributions over specific domains, which can vary widely across models. Besides some special cases where these integrals are easy to calculate, there exist no g...

Camouflage must be appreciated as an extraordinary feat of evolution, but any detection of such camouflaged objects by predator and prey is also an impressive feat of visual systems. Many historical studies of camouflage have focused on descriptive compilations or heuristic applications. Our goal instead is to understand camouflage detection in the...

The sensitivity index d’ is used ubiquitously to express the error rate in classification and detection tasks. In the general case with multiple cues that can have arbitrary variances and pairwise correlations, and unequal prior class probabilities, the decision boundary separating the classes is a complex surface. This makes it challenging to comp...

Understanding the mechanisms of neural computation and learning will require knowledge of the underlying circuitry. Because it is slow, expensive, or often infeasible to directly measure the wiring diagrams of neural microcircuits, there has long been an interest in estimating them from neural recordings. We show that even sophisticated inference a...

Occurrences of camouflage in nature evoke fascination and wonder in us. Less appreciated are the forces that shaped their evolution: the visual systems of their predators and prey. Indeed, having been filtered by them, camouflage specimens — no matter how ingenious — are poised near the edge of detectability, their inventiveness only testifying to...

We present some theoretical results on depth estimation from stereo image pairs, then describe the simple computational method of block-matching for doing this, with Matlab code and example results.

The thermal ratchets model toggles a spatially periodic asymmetric potential to rectify random walks and achieve transport of diffusing particles. We numerically solve the governing equation for the full dynamics of an infinite 1D ratchet model in response to periodic switching. Transient aperiodic behavior is observed that converges asymptotically...

Average displacement of a diffusing particle from its starting point is zero at all times. Hence, a population of such particles may only be transported in a particular direction by applying a drift-inducing external potential. However, a potential that exerts a force whose space-average is zero is not expected to result in transport (i.e. a flux w...

This report discusses a CUDA program to compare process times on a GPU and a CPU for a range of task size. The hardware compared are the NVIDIA® Tesla C870 GPU and the quad-core Intel® Xeon® E5410 CPU. The operation is to compute the square root of an array. Due to GPU restrictions, the array size is fixed and the operation repeated to increase the...

Why do railway tracks appear to meet at the horizon? Why do circles appear flattened when seen at an angle? What is a 'straight line'? Do we really see it as straight? How do we perceive depth? These are questions that relate to what we do all the time: see things. The sense of vision is fundamental to our perception of the world, yet most of us go...