In their 2004 study, Watanabe et al. measure the detectability of contrast increment probes during rivalry dominance and suppression by plotting threshold versus contrast (TvC)functions, finding significant elevation of detection thresholds during suppression. But what about contrast decrements, a probe that actually makes the target image harder to see? Here I review the literature on binocular rivalry and probe studies and measure the effect of two new probe types on detection thresholds. Results show that contrast decrement probes produce a very different pattern of detection thresholds than their increment counterparts. Extrapolating from these results, I also theorize on the effect of suppression on the underlying contrast response function (CRF).