Several encouraging developments towards identifying the neuronal correlate of visual awareness have emerged recently. Increasingly sophisticated behavioral paradigms permit the study of visual awareness in humans as ...
详细信息
Several encouraging developments towards identifying the neuronal correlate of visual awareness have emerged recently. Increasingly sophisticated behavioral paradigms permit the study of visual awareness in humans as well as in non-human primates. In patients with anatomically restricted lesions in striate and extrastriate cortex, highly informative deficits of visual awareness are observed. Similar deficits can be obtained in normal observers with a novel class of psychophysical displays. Taken together, these results suggest that the contents of visual awareness reflect neuronal activity in certain extrastriate, but not in striate, visual cortical areas.
Input noise, defined as the root mean square of the fluctuations in the input, typically limits the performance of any system in engineering or biology. We show that three different performance measures scale identica...
Input noise, defined as the root mean square of the fluctuations in the input, typically limits the performance of any system in engineering or biology. We show that three different performance measures scale identically as a function of the noise in a simple model of neuronal spiking that has both a voltage and current threshold. These performance measures are: the probability of correctly detecting a constant input in a limited time, the signal-to-noise ratio in response to sinusoidal input, and the mutual information between an arbitrarily varying input and the output spike train of the model neuron. Of these, detecting a constant signal is the simplest and most fundamental quantity. For subthreshold signals, the model exhibits stochastic resonance, a non-zero noise amplitude that optimally enhances signal detection. in this case, noise paradoxically does not limit but instead improves performance. This resonance arises through the conjunction of two competing mechanisms: the noise-induced linearization ('dithering') of the model's firing rate and the increase in the variability of the number of spikes in the output. Even though the noise amplitude dwarfs the signal, detection of a weak constant signal using stochastic resonance is still possible when the signal elicits on average only one additional spike. Stochastic resonance could thus play a role in neurobiological sensory systems, where speed is of the utmost importance and averaging over many individual spikes is not possible.
In this paper we describe an analog VLSI circuit, fabricated using a standard 2 mu m, n-well, BiCMOS process, which utilizes floating-gate structures for non-volatile, on-chip, analog parameter storage. This circuit i...
详细信息
In this paper we describe an analog VLSI circuit, fabricated using a standard 2 mu m, n-well, BiCMOS process, which utilizes floating-gate structures for non-volatile, on-chip, analog parameter storage. This circuit is designed to operate in the context of a hardware model of the primate oculomotor system and performs visually-guided, saccadic adaptation. The chip contains a one-dimensional array of photoreceptors and floating-gate circuits which are used to map retinal positions to motor output commands. The system's functionality is demonstrated by training the chip with several different mapping functions using a supervised-learning technique.
Intermediate and higher vision processes require selection of a subset of the available sensory information before further processing. Usually, this selection is implemented in the form of a spatially circumscribed re...
详细信息
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...
详细信息
ISBN:
(纸本)0262100762
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-/im analog CMOS VLSI process. The re-sult 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.
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...
详细信息
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.
Synthetic neuralsystems that operate in real time have been fabricated using analog complementary metal-oxide-semiconductor (CMOS) very large scale integration (VLSI) technology. The analog silicon system surpasses t...
详细信息
Shunting inhibition, a conductance increase with a reversal potential close to the resting potential of the cell, has been shown to have a divisive effect on subthreshold excitatory postsynaptic potential amplitudes. ...
Shunting inhibition, a conductance increase with a reversal potential close to the resting potential of the cell, has been shown to have a divisive effect on subthreshold excitatory postsynaptic potential amplitudes. It has therefore been assumed to have the same divisive effect on firing rates. We show that shunting inhibition actually has a subtractive effect on the firing rate in most circumstances. Averaged over several interspike intervals, the spiking mechanism effectively clamps the somatic membrane potential to a value significantly above the resting potential, so that the current through the shunting conductance is approximately independent of the firing rate. This leads to a subtractive rather than a divisive effect. In addition, at distal synapses, shunting inhibition will also have an approximately subtractive effect if the excitatory conductance is not small compared to the inhibitory conductance. Therefore regulating a cell's passive membrane conductance-for instance, via massive feedback-is not an adequate mechanism for normalizing or scaling its output.
暂无评论