Orientation column

About: Orientation column is a research topic. Over the lifetime, 1142 publications have been published within this topic receiving 130169 citations.

Characteristics of inhibition in receptive fields of the cat visual cortex

Abstract: Unit responses of neurons of zone 17 in the cat striate cortex to stripes of different widths were studied. Changes in the number of spikes during different time intervals (cuts) from the beginning of the response were analyzed in relation to stimulus area. Comparison of the results with those obtained by the study of receptive fields of the lateral geniculate body showed a significant difference in the dynamics of inhibition between cortical and geniculate receptive fields. Similar results were obtained when cortical unit responses to simultaneous and consecutive appearance of two stripes in the receptive field, one in the excitatory zone and the other at the inhibitory periphery, were studied. Evidence of the longer duration of cortical inhibition also was obtained by the same technique. When both stripes were placed in the excitatory center of the field another feature of cortical inhibition was revealed: its dependence on the order of stimulus application. If the order of stimulus application coincided with the optimal direction of movement of the stripe for the given field, the unit response to the next stimulus was strongly facilitated by the action of the stimulus applied previously. Application of stimuli in the opposite order invoked inhibition. The sensitivity of inhibition to the order of stimulus application was observed in the center of the field; it diminished toward the periphery, where application of the stimuli in any order evokes inhibition of the response.

Role of the visual environment in the formation of receptive fields according to the BCM theory.

Abstract: Publisher Summary The Bienenstock, Cooper, and Munro (BCM) theory of synaptic plasticity models the development of orientation selectivity and binocular interaction in primary visual cortex, and has successfully reproduced kitten visual deprivation experiments. To better compare the consequences of the BCM theory with experiment, the original abstraction of the visual environment is replaced in this chapter by real visual images. Circular regions from the left and right retinas covering the same visual space are used to generate input to a single BCM neuron. The lateral geniculate nucleus is assumed to simply relay signals generated in the retina to the visual cortex. Each ganglion selects an antagonistic center-surround receptive field generated by a difference of two Gaussians, and ganglion cell activity is restricted to be positive. This extension allows the BCM neuron to be trained and tested with static real two-dimensional images. The visual environment is represented by 24 gray scale natural images, which can be shifted across the artificial retinas. In this environment, the BCM neuron develops receptive similar to simple cells found in primary visual cortex. It displays adjacent excitatory and inhibitory bands, when tested with spot stimuli, and orientation selectivity when tested with bar stimuli.

Rapid adaptation and efficient coding.

Abstract: Rapid adaptation is a prominent feature of biological neuronal systems. From a functional perspective the adaptation of neuronal properties, namely the input-output relation of sensory neurons, is usually interpreted as an adaptation of the sensory system to changing environments as characterized by their stimulus statistics. Here we argue that this interpretation is only applicable as long as the adaptation processes are slower than the time-scale at which the stimulus statistics change. We present a definition of optimality of a neuronal code which still captures the idea of efficient coding, but which can also explain rapid adaptation without referring to an adaptation to different sensory environments. Finally, we apply our new idea to a simple model of an orientation hypercolumn in the primary visual cortex and predict that the interactions between orientation columns should adapt at the time-scale of a single stimulus presentation.

A functional model of the wiring of the simple cells of visual cortex

Abstract: A computer model of the simple cells in the mammalian visual cortex was constructed. The model cells received inputs from a great number of isopolar centre/surround cells assumed to be located in the lateral geniculate nucleus (LGN). The distribution of input to the model simple cells was either inhibitory/ excitatory or inhibitory/excitatory/inhibitory. Such arrangements produced receptive fields containing four or five consecutively antagonistic subfields. Responses produced by the model cells to different types of stimuli (periodical as well as nonperiodical) were obtained and compared to responses of living cells reported from various laboratories under comparable stimulus conditions. In all the situations tested, the responses of the model cells corresponded qualitatively very well to those of living cells. It was seen that the same wiring mechanism was able to account for orientation selectivity, spatial frequency filtering, various phase relationships between stimulus and response, subfield orientational selectivity, and slight end-inhibition. Furthermore, the receptive fields of the model simple cells closely resemble Gabor functions.