The neural locus of IOS is unlikely to be in V1 or V2. Whereas IOS was found to reduce the neural activity associated with a target stimulus in V1 (Sengpiel, Baddeley, Freeman, Harrad, & Blakemore,
1998; Sengpiel, Blakemore, & Harrad,
1995; Sengpiel & Blakemore,
1994), the subjective awareness of the target stimulus did not correlate with firing rates, LFP power, or fMRI BOLD response in V1 (Maier et al.,
2008; Wilke, Logothetis, & Leopold,
2006). Rather, a strong correlation between the subjective percept under IOS and neural activity was only found in higher visual areas, such as V3a and LOC (Fang & He,
2005; Hesselmann & Malach,
2011). Likewise, in binocular rivalry, a form of interocular suppression, a subjectively suppressed stimulus was found to still evoke neural activity in about 80% of the cells in V1/V2, 60% of cells in V4/MT, and 10% of cells in IT (Leopold & Logothetis,
1996; Logothetis & Schall,
1989; Sheinberg & Logothetis,
1997). In behavioral studies, the lower level features of a stimulus, such as spatial frequency (Blake & Fox,
1974; Blake et al.,
2006), orientation (Wade & Wenderoth,
1978), and color (White, Petry, Riggs, & Miller,
1978) are found to be less affected by binocular rivalry. Taken together, these results suggest that while IOS has a measureable impact on the neural response to a target stimulus in the early stages of visual processing, such as V1 and V2, its impact in these early stages is insufficient to affect a target's percept.