Using interocular suppression and EEG to study semantic processing.

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see Review of Kang et al. Presenting an image to one eye and a dissimilar image to the other eye induces a phenomenon called binocular rivalry, in which the conscious percept alternates between the two dissimilar images despite constant retinal input. This technique has provided some insight regarding the levels of visual processing that can take place outside awareness (for review, see Lin and He, 2009). To meticulously study the neu-ral correlates of awareness, binocular rivalry has, however, some disadvantages. Perceptual dominance durations only last a few seconds and switches are highly unpredictable. To ensure a long-lasting stable percept, Tsuchiya and Koch (2005) introduced a technique called continuous flash suppression (CFS), in which one of the eyes is presented with a dynamic noise pattern changing typically every 100 ms. Such a mask has proven to effectively dominate over the image presented to the other eye, rendering it consciously invisible. It remains unclear whether flash-suppressed stimuli are processed up to the semantic level. Originally, Zimba and Blake (1983) reported that no semantic priming occurred when prime words were suppressed from awareness through binocular rivalry. However, a recent study showed that participants see a target word faster through a CFS mask (i.e., break through suppression) when it was preceded by a related visible prime word (Costello et al., 2009). In a recent issue of The Journal of Neuroscience, Kang et al. (2011) tried to resolve this debate by combining interocular suppression and EEG recordings. Specifically, they focused on N400, a negative peak occurring ϳ400 ms after an unexpected stimulus, which is associated with semantic processing (Kutas and Federmeier, 2011). Previous studies demonstrated that words elicit smaller N400 amplitudes when preceded by semantically related primes than when preceded by unrelated primes (for references, see Kang et al., 2011). Building on these results, Kang et al. (2011) used interocular suppression to render either prime or target words invisible and investigate how this affects N400. In Experiments 1, 2, and 4, Kang et al. (2011) used CFS to render target words invisible after a prime word was presented. Participants had to signal whether the target word …