Topic
Orientation column
About: Orientation column is a research topic. Over the lifetime, 1142 publications have been published within this topic receiving 130169 citations.
Papers published on a yearly basis
Papers
More filters
01 Nov 2013
01 Jan 1993
TL;DR: A functional model called ED-chan is suggested to explore the meaning or usefulness of orientation specificity, and the results show that intermediate features such as ends, corners and crosses are being abstracted through self-organization.
Abstract: We propose an €&-chart, lmergent Local Indicator Mechanism, to model the representation and selforganization of intermediate features in the visual pathway. This model is motivated by the orientation specificity in the primary visual cortex. Our simulations of €@-chan demonstrate that local indicators of the locations of intermediate features emerge, and they become the seeds for unsupervised learning and pattern recognition; €0-chan predicts those portions of the input imagery where intermediate features potentially exist. Hence, E&-chun can be used to define a set of intermediate features for adaptation, and the onwards processing in a hierarchical pattern recognition system. Visual pathway processes information hierarchically, so that the external world is perceived via a series of feature abstractions. At the primary level, simple cells and complex cells in the primary visual cortex exhibit orientation specificity; the visual world is being dissected into line segments of various orientations. Furthermore, neurons with the same orientation specificity are grouped together into orientation columns, and these columns are regularly arranged in a stepwise or quasi-continuous fashion from Oo to 360°, to cater for all possible orientations in a given area of the visual field [l]. Why is the primary visual cortex (area 17) organized according to orientation specificity? While it is apparent that the decomposition of the visual world into line segments of various orientations is necessary for the discrimination of form and movement in the early vision, its significance for the representation of features at the intermediate level (area 18) is not well understood. In this paper, we suggest a functional model called ED-chan to explore the meaning or usefulness of orientation specificity. We have simulated lfi-chan on personal computer, and the results show that intermediate features such as ends, corners and crosses are being abstracted through self-organization. With €0-chan, we can construct a hierarchical neural net to self-learn and recognize objects in the visual world.
TL;DR: Three functional classes of neurons are described in the visual cortex of the Siberian chipmunk: neurons not selective for direction of movement and orientation, neuron selective for movement in a particular direction, and neurons selective for orientation.
Abstract: Three functional classes of neurons are described in the visual cortex of the Siberian chipmunk: neurons not selective for direction of movement and orientation, neurons selective for movement in a particular direction, and neurons selective for orientation. Unselective and directionally-selective neurons were activated maximally at speeds of movement of 100–500 deg/sec or more, most orientation-selective neurons at speeds of 10–50 deg/sec. For all three classes of neurons clear correlation was observed between selectivity for velocity of movement and character of responses to presentation of stimuli stationary in the receptive field. With reference to this sign the neurons were divided into two groups: phasic (fast) and tonic (slow). Phasic (fast) neurons predominate in the visual cortex ofEutamias sibiricus.
01 Jan 1999
TL;DR: A model of the development of corpus callosum connections in cat visual cortex showed how the observed hour-glass pattern of callosal receptive field (RF) positions arises as a consequence of the retinotopic mapping onto the cortex.
Abstract: Many previous models have explained how ocular dominance- and orientation selective columns could develop in the visual cortex. However, few models have investigated the topographic arrangement of interhemispheric connections between primary visual areas. A model of the development of corpus callosum connections in cat visual cortex was presented by Hely (1999). The model showed how the observed hour-glass pattern of callosal receptive field (RF) positions arises as a consequence of the retinotopic mapping onto the cortex. In the cat, callosal connections only form between cells with visual field RFs located close to the vertical meridian. In contrast in rat visual cortex, callosal connections also form between cells with RFs in the peripheral visual field. This cannot be accounted for using a Hebbian rule based on spatial information alone. The current generic model of primary visual cortex was extended by including optic-flow/motion information. This extra input enabled cells with peripheral RFs fields in the medial cortex to make connections to the opposite hemisphere. The results from the model suggest that in some species motion information may affect the development of connections in primary visual cortex.
TL;DR: Studies of orientational tuning and its dynamics during generation of responses in neurons located in orientation columns and the centers of orientation pinwheels in the primary visual cortex of the cat show that stable neurons in pinwheel centers had shorter latent periods and larger responses than neurons in orientation Columns.
Abstract: We report here studies of orientational tuning and its dynamics during generation of responses in neurons located in orientation columns and the centers of orientation pinwheels in the primary visual cortex of the cat. Intrinsic signal optical mapping was used to define the position of the working module on functional and vascular maps of the cortical surface. Both maps were used for targeted implantation of microelectrodes. The dynamics of orientational tuning were studied using a time slice method. Neurons whose preferred orientations were stable during response generation were observed in pinwheel centers and in orientation columns, accounting for 14.5% of cells, along with neurons in which the preferred orientation sequentially shifted by an average of 102 ± 5° (40.8%) and neurons with mixed-type dynamics (44.7%). Neurons with stable tuning in pinwheel centers differed from neurons with unstable tuning by producing greater responses to the preferred orientation, while those in orientation columns were characterized by later onset of responses to all orientations, including the preferred and non-preferred orientations. The orientational qualities of detection in stable neurons in these functional modules were better than those of cells with unstable tuning. Comparison of neurons with the same type of preferred orientation dynamics but different locations showed that stable neurons in pinwheel centers had shorter latent periods and larger responses than neurons in orientation columns. The width and selectivity of orientation tuning in these cells showed no differences. In unstable neurons, the characteristics of orientation tuning and responses to the preferred orientation were independent of location and were essentially identical. The functional significance of neurons with stable and unstable tuning during response generation in pinwheel centers and orientation columns in the primary visual cortex is discussed