Abstract
The stability of fusion was evaluated by its breakage when interocular blur differences were presented under vergence demand to healthy subjects. We presumed that these blur differences cause suppression of the more blurred image (interocular blur suppression, IOBS), disrupt binocular fusion and suppressed eye leaves its forced vergent position. During dichoptic presentation of static grayscale images of natural scenes, the luminance contrast (mode B) or higher-spatial frequency content (mode C) or luminance contrast plus higher-spatial frequency content (mode A) were stepwise reduced in the image presented to the non-dominant eye. We studied the effect of these types of blur on fusion stability at various levels of the vergence demand. During the divergence demand, the fusion was disrupted with approximately half blur than during convergence. Various modes of blur influenced fusion differently. The mode C (isolated reduction of higher-spatial frequency content) violated fusion under the lowest vergence demand significantly more than either isolated or combined reduction of luminance contrast (mode B and A). According to our results, the image´s details (i.e. higher-spatial frequency content) protects binocular fusion from disruption by the lowest vergence demand.
Highlights
Binocular fusion is a key mechanism of normal vision
The artificial manipulation of the image quality of the non-dominant eye while the dominant eye was continuously stimulated by the normal image resulted in a progressive increase in the interocular blur difference
The absence of a disparity signal caused the disruption of disparity vergence mechanisms and the suppressed non-dominant eye left its forced vergent position
Summary
Binocular fusion is a key mechanism of normal vision. The proper combination of monocular signals is a crucial step preceding higher associative processes. Whereas the early phases of spatial frequency and other first order signal processing are located to the central occipital region (De Cesarei, Mastria, & Codispoti, 2013), second order and associative analysis progressively engages the lateral occipital cortex, temporo-parietal junction and higher association cortical areas (Buckthought, Jessula, & Mendola, 2011). This neuroanatomy supports a highly probable relationship of binocular rivalry to other suppressive phenomena such as motion-induced blindness (Jaworska & Lages, 2014) and dichoptic masking (van Boxtel, van Ee, & Erkelens, 2007). The latter is assumed to share with binocular rivalry the processing abilities of monocular neurons at V1 (Baker & Graf, 2009b; Baker & Meese, 2007; Huang, Baker, & Hess, 2012)
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