The Source of Overlay Masking in the Human Visual System

摘要

The cortical response to an oriented pattern is influenced by the superimposition of a pattern of orthogonal orientation. This phenomenon, termed overlay masking (alternatively, cross-orientation suppression), manifests as a reduction in effective contrast that could be attributed to either primarily cortical or subcortical mechanisms. Here, we used source- imaged electroencephalography (EEG) to identify the source of overlay masking in the human visual system. We measured the response of neurons in primary visual cortex (V1) to an oriented test component of varying contrast, and examined how this response was altered by the superimposition of an orthogonal mask presented to the same eye (monoptic) or different eye (dichoptic). We found that a monoptic mask changed the effective contrast of the test component, consistent with overlay masking, while a dichoptic mask preserved the effective contrast of the test component and hence circumvented overlay masking. Given that dichoptic presentation precludes subcortical interactions between components, we identify subcortical mechanisms as the primary source of overlay masking in the human visual system.