Issues That Remain Unanswered

In this chapter, I examined the possibility that quick detection of snakes is achieved not only by subcortical visual pathway but also by cortical processing such as V2 and V4. A larger EPN for snake pictures, which is considered to occur from visual cortical areas, emerges around 200 ms after the onset of the stimulus. It is thought to result from automatic selective visual attention to emotional stimuli, which may evoke priority processing because of their intrinsic affective significance, with the amygdala modulating activity in the visual cortex. Humans can identify one face among possible six faces, even if the stimuli were followed by a masking stimulus only 20–30 ms after the stimulus onset. Our recent study showed that macaques could select one target image among eight distractors, even when these images were followed by masking patterns after 50 ms. These suggest that visual information is processed by cortical areas as fast as subcortical areas at least for a single image. Early visual areas such as V2 and V4 play important role to discriminate textures. Snake skin (scale) constitutes a uniform texture. If snake scale is a critical feature to detect snakes for primates and humans, V2 and V4 may contribute to detect snakes quickly, which activations may be reflected as a larger EPN. I conclude this chapter with future directions for the better understanding of fear of snakes.