Lateral facilitation revealed dichoptically for luminance-modulated and contrast-modulated stimuli

Foveal detection thresholds for LM and CM Gaussian blobs in the presence of visible, laterally placed blobs (separations of 0-6°) were measured monocularly and dichoptically in observers with normal vision. In the monocular and dichoptic viewing conditions, masking occurs for overlapping blobs, followed by facilitation when they are completely separated (2-8 blob sd units under monocular conditions and 4-12 blob sd units under dichoptic conditions). For LM blobs, facilitation of 24.1±0.07% is demonstrated dichoptically, less than the 57.0±0.06% demonstrated monocularly. For CM blobs, more robust facilitation of 39.0±0.02% is demonstrated dichoptically, slightly more than the 34.6±0.1% demonstrated monocularly. Lateral facilitation is thus not purely a monocular phenomenon. More robust dichoptic facilitation for CM stimuli suggests a more binocular locus for their neural processing.