Our previous research examined the effects of target eccentricity and global stimulus density on target detection during active visual search in monkey. Here, eye movement data collected from three human subjects on a standard single-color Ts and Ls task with varying set sizes were used to analyze the probability of target detection as a function of local stimulus density. Search performance was found to exhibit a systematic dependence on local stimulus density around the target and as a function of target eccentricity when density is calculated with respect to cortical space, in accordance with a model of the retinocortical geometrical transformation of image data onto the surface of V1. Density as measured by nearest neighbor separation and target image size as calculated from target eccentricity were found to contribute independently to search performance when measured with respect to cortical space but not with standard visual space. Density relationships to performance did not differ when target and nearest neighbor were on opposite sides of the vertical meridian, underscoring the hypothesis that such interactions were occurring within higher visual areas. The cortical separation of items appears to be the major determinant of array set size effects in active visual search.
The size of the functional visual field (FVF) is dynamic, changing with the context and attentive demand that each fixation brings as we move our eyes and head to explore the visual scene. Using performance measures of the FVF we show that during search conditions with eye movements, the FVF is small compared to the size of the FVF measured during search without eye movements. In all cases the size of the FVF is constrained by the density of distracting items. During search without eye movements the FVF expands with time; subjects have idiosyncratic spatial biases suggesting covert shifts of attention. For search within the constraints imposed by item density, the rate of item inspection is the same across all search conditions. Array set size effects are not apparent once stimulus density is taken into account, a result that is consistent with a spatial constraint for the FVF based on the cortical separation hypothesis.
SUMMARY MOVIE (Multitasking Object-oriented Visual Interactive Envlronment) is a new software system for high-performance distributed computing (HPDC), currently In the advanced design and impicmentatlon stage at Northeast Parallel Architectures Center (NPAC), Syracuse University. The MOVIE system is structured as a rnuitlserver network of Interpreters of the high-level object-oriented programming language MovieScript. MovieScript derives lrom PostScript and extcnds it In the C++ syntax-based obJect-orlented interpreted style towards 3D graphics, high-performance computing and general-purpose high-level communication protocol for distributed and MIMD-prraiici computing. The paper describes the overall open systems-based MOVIE design and itemizes currently Implemented, developed and planned componcnts of the system.
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