The long-term objective of the proposed research is to understand the neuronal mechanisms underlying scene segmentation by the mammalian visual system. In this process, the visual system is thought to parse a scene into its component objects by identifying relationships among common features. A critical step in segmentation is the grouping of oriented features into contours that form the boundaries of objects. Current evidence indicates that striate cortex makes a fundamental contribution to this process of contour integration, but the underlying neuronal representations are not fully understood. In the proposed research, we plan to monitor the activity of groups of neurons at two or more sites in striate cortex of behaving macaque monkeys, in order to test three specific hypotheses for the neuronal correlate of contour integration. We will conduct two sets of experiments in which we will establish the relations between contour salience, neuronal activity and behavioral performance. In the first experiment, the animals will be required to signal their detection of a peripheral contour embedded in a background by making a saccadic eye movement to its location after a central fixation target is extinguished. In the second experiment, the animals will be cued to select one of two adjacent contours embedded in a background by making a saccadic eye movement to the cued contour after a central fixation target is extinguished. In both experiments, the contour salience, and hence the task difficulty, will be controlled by varying the orientation of the elements comprising the contour. The visual stimuli will be composed of arrays of randomly oriented Gabor patches, in which one or two subsets of the patches will be aligned to form a closed contour. Elements of the contour(s) or background will be positioned over the cellular receptive fields to activate the recorded neurons. This paradigm will enable us to keep the local stimuli activating the cells constant while systematically manipulating the figure/ground relationships, the perceptual salience and the behavioral relevance of the contours. We will analyze the resulting activities to determine if contour integration is correlated with specific changes in firing rates, temporal correlations, response latencies or some combination of these variables. Together, these experiments will enable us to investigate the neuronal correlate of contour integration in striate cortex, and advance our understanding of scene segmentation processes in general.
| Herikstad, Roger; Baker, Jonathan; Lachaux, Jean-Philippe et al. (2011) Natural movies evoke spike trains with low spike time variability in cat primary visual cortex. J Neurosci 31:15844-60 |
