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Subash Sukumar, Sarah J Waugh; Spatial extent and eccentricity effects for detection of luminance-defined and contrast-defined blob stimuli. Journal of Vision 2003;3(9):347. doi: https://doi.org/10.1167/3.9.347.
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© ARVO (1962-2015); The Authors (2016-present)
Evidence from masking studies suggests that the detection of luminance-defined and contrast-defined spatial stimuli under foveal viewing conditions are detected by independent mechanisms (Schofield and Georgeson, 1999). Results also indicated similarly sized spatial integration regions for these foveally-viewed stimuli. The aim of this study is to further characterise spatial summation regions for the detection of luminance-defined and contrast-defined stimuli at the fovea and in the periphery.
Luminance-defined stimuli were constructed by adding random dot noise to a Gaussian profile, whereas contrast-defined stimuli were constructed by multiplying random dot noise to a Gaussian profile. Random dot noise was dynamic and care was taken to eliminate unwanted artefacts. Blobs varied in size from a sigma of 0.06 deg to 2 deg and were presented for 400 msec. Detection thresholds for all sizes were measured at the fovea and at 2.5, 5 and 10 deg in the inferior visual field. A self-paced, temporal 2AFC paradigm was used to obtain performance estimates.
Spatial summation areas for contrast-defined and luminance-defined stimuli obtained under foveal viewing were similar in extent, confirming the previous result. However for all measured eccentricities, spatial integration areas for contrast-defined stimuli were larger than those found for luminance-defined stimuli. Detection thresholds obtained for single-sized stimuli at the different eccentricities also reveal a steeper rate of fall-off for contrast-defined stimuli than for luminance-defined stimuli.
These results suggest that in peripheral vision, different underlying processes limit the detection of luminance-defined and contrast-defined spatial targets.
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