Simplified models of the lateral geniculate nucles (LGN) and striate cortex illustrate the possibility that feedback to the LGN may be used for robust, low-level pattern analysis. The information fed back to the LGN i...
ISBN:
(纸本)9781558602748
Simplified models of the lateral geniculate nucles (LGN) and striate cortex illustrate the possibility that feedback to the LGN may be used for robust, low-level pattern analysis. The information fed back to the LGN is rebroadcast to cortex using the LGN's full fan-out, so the cortex→LGN→cortex pathway mediates extensive cortico-cortical communication while keeping the number of necessary connections small.
Here we derive measures quantifying the information loss of a synaptic signal due to the presence of neuronal noise sources, as it electrotonically propagates along a weakly-active dendrite. We model the dendrite as a...
Here we derive measures quantifying the information loss of a synaptic signal due to the presence of neuronal noise sources, as it electrotonically propagates along a weakly-active dendrite. We model the dendrite as an infinite linear cable, with noise sources distributed along its length. The noise sources we consider are thermal noise, channel noise arising from the stochastic nature of voltage-dependent ionic channels (K+ and Na+) and synaptic noise due to spontaneous background activity. We assess the efficacy of information transfer using a signal detection paradigm where the objective is to detect the presence/absence of a presynaptic spike from the post-synaptic membrane voltage. This allows us to analytically assess the role of each of these noise sources in information transfer. For our choice of parameters, we find that the synaptic noise is the dominant noise source which limits the maximum length over which information be reliably transmitted.
In an effort to understand saccadic eye movements and their relation to visual attention and other forms of eye movements, we - in collaboration with a number of other laboratories - are carrying out a large-scale eff...
In an effort to understand saccadic eye movements and their relation to visual attention and other forms of eye movements, we - in collaboration with a number of other laboratories - are carrying out a large-scale effort to design and build a complete primate oculomotor system using analog CMOS VLSI technology. Using this technology, a low power, compact, multi-chip system has been built which works in real-time using real-world visual inputs. We describe in this paper the performance of an early version of such a system including a 1-D array of photoreceptors mimicking the retina, a circuit computing the mean location of activity representing the superior colliculus, a saccadic burst generator, and a one degree-of-freedom rotational platform which models the dynamic properties of the primate oculomotor plant.
Flies are capable of rapidly detecting and integrating visual motion information in behaviorly-relevant ways. The first stage of visual motion processing in flies is a retinotopic array of functional units known as el...
Flies are capable of rapidly detecting and integrating visual motion information in behaviorly-relevant ways. The first stage of visual motion processing in flies is a retinotopic array of functional units known as elementary motion detectors (EMDs). Several decades ago, Reichardt and colleagues developed a correlation-based model of motion detection that described the behavior of these neural circuits. We have implemented a variant of this model in a 2.0-µm analog CMOS VLSI process. The result is a low-power, continuous-time analog circuit with integrated photoreceptors that responds to motion in real time. The responses of the circuit to drifting sinusoidal gratings qualitatively resemble the temporal frequency response, spatial frequency response, and direction selectivity of motion-sensitive neurons observed in insects. In addition to its possible engineering applications, the circuit could potentially be used as a building block for constructing hardware models of higher-level insect motion integration.
The localization and orientation to various novel or interesting events in the environment is a critical sensorimotor ability in all animals, predator or prey. In mammals, the superior colliculus (SC) plays a major ro...
The localization and orientation to various novel or interesting events in the environment is a critical sensorimotor ability in all animals, predator or prey. In mammals, the superior colliculus (SC) plays a major role in this behavior, the deeper layers exhibiting topographically mapped responses to visual, auditory, and somatosensory stimuli. Sensory information arriving from different modalities should then be represented in the same coordinate frame. Auditory cues, in particular, are thought to be computed in head-based coordinates which must then be transformed to retinal coordinates. In this paper, an analog VLSI implementation for auditory localization in the azimuthal plane is described which extends the architecture proposed for the barn owl to a primate eye movement system where further transformation is required. This transformation is intended to model the projection in primates from auditory cortical areas to the deeper layers of the primate superior colliculus. This system is interfaced with an analog VLSI-based saccadic eye movement system also being constructed in our laboratory.
Here we analyze synaptic transmission from an information-theoretic perspective. We derive closed-form expressions for the lower-bounds on the capacity of a simple model of a cortical synapse under two explicit coding...
Here we analyze synaptic transmission from an information-theoretic perspective. We derive closed-form expressions for the lower-bounds on the capacity of a simple model of a cortical synapse under two explicit coding paradigms. Under the "signal estimation" paradigm, we assume the signal to be encoded in the mean firing rate of a Poisson neuron. The performance of an optimal linear estimator of the signal then provides a lower bound on the capacity for signal estimation. Under the "signal detection" paradigm, the presence or absence of the signal has to be detected. Performance of the optimal spike detector allows us to compute a lower bound on the capacity for signal detection. We find that single synapses (for empirically measured parameter values) transmit information poorly but significant improvement can be achieved with a small amount of redundancy.
We investigate the dynamics of large arrays of coupled phase oscillators driven by random intrinsic frequencies under a variety of coupling schemes, by computing the time-dependent cross-correlation function numerical...
We investigate the dynamics of large arrays of coupled phase oscillators driven by random intrinsic frequencies under a variety of coupling schemes, by computing the time-dependent cross-correlation function numerically for a two-dimensional array consisting of 128×128 oscillators as well as analytically for a simpler model. Our analysis shows that for overall equal interaction strength, a sparse-coupling scheme in which each oscillator is coupled to a small, randomly selected subset of its neighbors leads to a more rapid and robust phase locking than nearest-neighbor coupling or locally dense connection schemes.
Monotonicity is a constraint which arises in many application domains. We present a machine learning model, the monotonic network, for which monotonicity can be enforced exactly, i.e., by virtue of functional form. A ...
Monotonicity is a constraint which arises in many application domains. We present a machine learning model, the monotonic network, for which monotonicity can be enforced exactly, i.e., by virtue of functional form. A straightforward method for implementing and training a monotonic network is described. Monotonic networks are proven to be universal approximators of continuous, differentiable monotonic functions. We apply monotonic networks to a real-world task in corporate bond rating prediction and compare them to other approaches.
Frequency modulations in acoustic communication signals are thought to encode meaning in many animal species. Recent physiological experiments have elucidated possible neural mechanisms underlying their perception. Th...
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Frequency modulations in acoustic communication signals are thought to encode meaning in many animal species. Recent physiological experiments have elucidated possible neural mechanisms underlying their perception. The system described here attempts to model such mechanisms using subthreshold analog circuitry. It is built with a silicon cochlea and a unidirectional velocity-tuned delay line. Taps from the cochlea couple into the delay line. If the input frequency is modulated in the appropriate direction and right speed, the inputs to the delay line will coincide in time and summate. A similar design was recently used to detect motion in a vision chip.
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
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