Separate first- and second-order processing is supported by spatial summation estimates at the fovea and eccentrically.
We estimated spatial summation areas for the detection of luminance-modulated (LM) and contrast-modulated (CM) blobs at the fovea, 2.5, 5 and 10 deg eccentrically. Gaussian profiles were added or multiplied to binary white noise to create LM and CM blob stimuli and these were used to psychophysically estimate detection thresholds and spatial summation areas. The results reveal significantly larger summation areas for detecting CM than LM blobs across eccentricity. These differences are comparable to receptive field size estimates made in V1 and V2. They support the notion that separate spatial processing occurs for the detection of LM and CM stimuli.
Sukumar
Subash
S
University of Manchester, Department of Ophthalmology, Manchester Royal Eye Hospital, Oxford Road, M13 9WH, UK. subash.sukumar@manchester.ac.uk
Waugh
Sarah J
SJ
D015350:Contrast Sensitivity / Q000502:physiology*; D005584:Fovea Centralis / Q000502:physiology*; D006801:Humans; D008029:Lighting; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology; D014794:Visual Fields