Strength of continuous flash suppression is optimal when target and masker modulation rates are matched

Abstract

Continuous flash suppression (CFS) is a popular technique whereby a dynamic sequence of Mondrian patterns is presented to one eye in order to suppress a static target presented to the other eye. Although the effectiveness of CFS is generally assumed to increase with the flicker rate of the Mondrian masker, a recent study has shown that suppression is optimal at very low masker rates for sustained targets, but higher rates may be necessary for transient targets. Here we vary the modulation rates of the masker and target using temporally filtered dynamic noise, which allowed us to examine the relationship between target and masker frequency and its effect on suppression strength. Using these carefully controlled, temporally narrowband stimuli, we demonstrate a pattern of results showing that suppression is greatest when target and masker modulate at similar frequencies. This finding indicates the involvement of early temporal-frequency-tuned filters underlying CFS and is consistent with many existing findings in the CFS literature. We also find that these temporally selective processes are orientation selective, which points to an early cortical substrate such as neurons in primary visual cortex. Overall, our study reveals that CFS suppression can be maximized by carefully matching the masker and target in temporal frequency and orientation. More generally, we show the importance of using carefully controlled stimuli for elucidating the underlying mechanisms of CFS. This approach is important at a theoretical level, as it will enable comparison of CFS with existing models of binocular rivalry and interocular suppression and facilitate a unified explanatory framework.