Tagged: Visual system

Perceptual salience as novelty detection in cortical pinwheel space

We describe a filter-based model of orientation processing in primary visual cortex (V1) and demonstrate that novelty in cortical “pinwheel” space can be used as a measure of perceptual salience. In the model, novelty is computed as the negative log likelihood of a pinwheel’s activity relative to the population response. The population response is modeled using a mixture of Gaussians, enabling the representation of complex, multi-modal distributions. Hidden variables that are inferred in the mixture model can be viewed as grouping or “binding” pinwheels which have similar responses within the distribution space. Results are shown for several stimuli that illustrate well-known contextual effects related to perceptual salience, as well as results for a natural image.

Texture discrimination and binding by a modified energy model

The model presented shows how textured regions can be discriminated and textured surface created by the visual cortex. The model addresses two major processes: texture segmentation and texture binding. Textures are detected by using a version of the energy model of J. R. Bergen and E. H. Adelson (1988) and J. R. Bergen and M. S. Landy (1991), which was modified to include ON and OFF center cells, and units selective for line endings. A novel neural mechanism is described for binding a texture pattern together. Simulation results demonstrated the ability of the networks to segment and bind a well-known texture pattern.

A neural network model of object segmentation and feature binding in visual cortex

The authors present neural network simulations of how the visual cortex may segment objects and bind attributes based on depth-from-occlusion. They briefly discuss one particular subprocess in the occlusion-based model most relevant to segmentation and binding: determination of the direction of figure. They propose that the model allows addressing a central issue in object recognition: how the visual system defines an object. In addition, the model was tested on illusory stimuli, with the network’s response indicating the existence of robust psychophysical properties in the system.