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.

Research highlights► Less facilitation is demonstrated dichoptically than monocularly for LM blobs. ► Lateral facilitation can also occur when target and flanks are of different type. ► Uncertainty reduction alone cannot explain the facilitatory effects. ► CM stimuli appear to be processed in a more binocular region than LM stimuli. ► Lateral interaction also occurs when target and flanks are of different type.