Bidirectionality in synesthesia and metaphor

Most studies of synesthesia have documented its unidirectional nature. For example, in grapheme-color synesthesia, a digit (e.g., 5) triggers a color (e.g., yellow) but not vice versa. This has led many to believe synesthesia is unidirectional. However, research has provided evidence that synesthesia might be bidirectional. Similarly, discussions of metaphors have suggested that metaphors are unidirectional and, in particular, move from the concrete to the abstract dimensions. For example, the smell of fish might induce suspicion ("Something smells fishy"). However, research has suggested that metaphors might work in the other direction also, namely, from abstract to concrete. For example, induction of suspicion leads to improved detection of the smell of fish than of other odors. Are these similarities between synesthesia and metaphors just superficial or do they tell us something about our cognitive mechanisms? The present paper reviews research on directionality in synesthesia and metaphors and attempts to propose some future research directions in order to answer this question.