Binocular rivalry between emotional and neutral stimuli: a validation using fear conditioning and EEG.

When two incompatible pictures are projected to the two eyes, they compete for perceptual dominance. Previous research has claimed that meaningful and emotionally valenced pictures predominate over neutral pictures in this rivalry. This may be interpreted as evidence for preferential processing of emotionally significant stimuli in the visual system but it is difficult to dismiss that the physical characteristics of the different pictures or response biases influenced the results of these studies. Thus, we set out to examine the influence of emotion using methods eliminating the influence of physical characteristics and minimizing response biases. We used simple visual patterns and induced emotional valence by fear conditioning. In Experiment 1 the aversive CS+ predominated over the CS-. In Experiment 2 we extended previous findings by showing that participants' self-reported perception is validated by corresponding steady-state visually evoked potentials in the EEG in the context of such a conditioning experiment. This was accomplished by frequency coding the rivalling stimuli with a stimulus specific pattern reversal and extracting the corresponding frequency from the occipital lobe EEG. Taken together, these studies provide further evidence that picture valence can influence perception in binocular rivalry. This is discussed in terms of subcortical mechanisms supporting the efficient processing of threatening information.