Biological retinas extract spatial and temporal features in an attempt to reduce the complexity of performing visual tasks. We have built and tested a silicon retina which encodes several useful temporal features foun...
ISBN:
(纸本)9781558602229
Biological retinas extract spatial and temporal features in an attempt to reduce the complexity of performing visual tasks. We have built and tested a silicon retina which encodes several useful temporal features found in vertebrate retinas. The cells in our silicon retina are selective to direction, highly sensitive to positive contrast changes around an ambient light level, and tuned to a particular velocity. Inhibitory connections in the null direction perform the direction selectivity we desire. This silicon retina is on a 4.6 × 6.8mm die and consists of a 47 × 41 array of photoreceptors.
Single nerve cells with static properties have traditionally been viewed as the building blocks for networks that show emergent phenomena. In contrast to this approach, we study here how the overall network activity c...
ISBN:
(纸本)9781558602229
Single nerve cells with static properties have traditionally been viewed as the building blocks for networks that show emergent phenomena. In contrast to this approach, we study here how the overall network activity can control single cell parameters such as input resistance, as well as time and space constants, parameters that are crucial for excitability and spatio-temporal integration. Using detailed computer simulations of neocortical pyramidal cells, we show that the spontaneous background firing of the network provides a means for setting these parameters. The mechanism for this control is through the large conductance change of the membrane that is induced by both non-NMDA and NMDA excitatory and inhibitory synapses activated by the spontaneous background activity.
The authors have designed, built and tested a number of analog CMOS VLSI circuits for computing 1D motion from the time-varying intensity values provided by an array of on-chip phototransistors. The authors present ex...
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The authors have designed, built and tested a number of analog CMOS VLSI circuits for computing 1D motion from the time-varying intensity values provided by an array of on-chip phototransistors. The authors present experimental data for three such circuits and discuss their relative performance. One circuit approximates the correlation model, one the gradient model, while a third chip uses resistive grids to compute zerocrossings to be tracked over time by a separate digital processor. All circuits integrate image acquisition with image processing functions and compute velocity in real time. Finally, for comparison, the authors also describe the performance of a simple motion algorithm using off-the-shelf components.< >
A method for transforming performance evaluation signals distal both in space and time into proximal signals usable by supervised learning algorithms, presented in [Jordan & Jacobs 90], is examined. A simple obser...
ISBN:
(纸本)9781558602229
A method for transforming performance evaluation signals distal both in space and time into proximal signals usable by supervised learning algorithms, presented in [Jordan & Jacobs 90], is examined. A simple observation concerning differentiation through models trained with redundant inputs (as one of their networks is) explains a weakness in the original architecture and suggests a modification: an internal world model that encodes action-space exploration and, crucially, cancels input redundancy to the forward model is added. Learning time on an example task, cartpole balancing, is thereby reduced about 50 to 100 times.
The accuracy of optical flow estimation depends on the spatio-temporal discretization used in the computation. The authors propose an adaptive multiscale method, where the discretization scale is chosen locally accord...
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The accuracy of optical flow estimation depends on the spatio-temporal discretization used in the computation. The authors propose an adaptive multiscale method, where the discretization scale is chosen locally according to an estimate of the relative error in the velocity measurements. They show that their coarse-to-fine method provides substantially better results of optical flow than conventional algorithms. The authors map this multiscale strategy onto their model of motion computation in primate area MT. The model consists of two stages: (1) local velocities are measured across multiple spatio-temporal channels, while (2) the optical flow field is computed by a network of direction-selective neurons at multiple spatial resolutions. Their model neurons show the same nonclassical receptive field properties as Allman's type I MT neurons and lead to a novel interpretation of some aspect of the motion capture illusion.< >
Tactile responses in the granule cell layers of the cerebellar hemispheres of rats are topographically arranged as a series of patches each representing a different region of the body surface. Previous observations ha...
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Tactile responses in the granule cell layers of the cerebellar hemispheres of rats are topographically arranged as a series of patches each representing a different region of the body surface. Previous observations had suggested that patches representing specific body parts recur in similar folial positions in different individuals;however, these relationships were not quantified. In this study we make inter-animal comparisons of the detailed distribution of receptive fields in the granule cell layer of the crown of crus IIa by using physiological mapping techniques. The results suggest that maps from different individuals do, in fact, share several topological features. These include the regions of the body surface represented, the general proportions of these representations, the relative position of patches representing the same body parts, and the organization of receptive fields within patches located in similar positions. The principal variability seen in these comparisons was in the detailed neighborhood relations between different patches. As a result of the analysis of the consistent and variable features of these maps, we propose and discuss a new role for these cerebellar regions in coordinating the acquisition of tactile sensory information.
A large number of computer vision algorithms for finding intensity edges, computing motion, depth, and color, and recovering the three-dimensional shape of objects have been developed within the framework of minimizin...
A large number of computer vision algorithms for finding intensity edges, computing motion, depth, and color, and recovering the three-dimensional shape of objects have been developed within the framework of minimizing an associated "energy" or "cost" functional. Particularly successful has been the introduction of binary variables coding for discontinuities in intensity, optical flow field, depth, and other variables, allowing image segmentation to occur in these modalities. The associated nonconvex variational functionals can be mapped onto analog, resistive networks, such that the stationary voltage distribution in the network corresponds to a minimum of the functional. The performance of an experimental analog very-large-scale integration (VLSI) circuit implementing the nonlinear resistive network for the problem of two-dimensional surface interpolation in the presence of discontinuities is demonstrated;this circuit is implemented in complementary metal oxide semiconductor technology.
Horizontal long-range interactions are strongly involved in the generation of the receptive fields of visual cortical cells. Structurally imposed limitations of long-range interactions are demonstrated. In particular,...
Horizontal long-range interactions are strongly involved in the generation of the receptive fields of visual cortical cells. Structurally imposed limitations of long-range interactions are demonstrated. In particular, it is shown that the cross-orientation inhibition scheme leads to inhomogeneous input for different cell populations which is experimentally not observed. This is not the case for circular inhibition, a new connection scheme proposed for long-range interaction. This is shown by computer simulation of the early visual system of the cat and by a simpler but analytically solvable model. The results are confirmed by applying the methods to the experimentally determined structure of the orientational hypercolumns in area 18 of the cat
Inspired by a visual motion detection model for the rabbit retina and by a computational architecture used for early audition in the barn owl, we have designed a chip that employs a correlation model to report the one...
ISBN:
(纸本)9781558601840
Inspired by a visual motion detection model for the rabbit retina and by a computational architecture used for early audition in the barn owl, we have designed a chip that employs a correlation model to report the one-dimensional field motion of a scene in real time. Using subthreshold analog VLSI techniques, we have fabricated and successfully tested a 8000 transistor chip using a standard MOSIS process.
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