Induced awareness of synesthetic sensations in synesthetically predisposed "Borderline Non-synesthetes"

A long-standing issue concerning synesthesia is whether the trait is continuous or discontinuous with ordinary perception. Here, we found that a substantial proportion of non-synesthetes (>10 % out of >200 unselected participants) spontaneously became aware of their synesthesia by participating in an online survey that forced them to select colors for stimuli that evoke color sensations in synesthetes. Notably, the test-retest consistencies of color sensation in these nonsynesthetes were comparable to those in self-claimed synesthetes, revealing their strong though latent synesthetic dispositions. The effect was absent or weak in a matched control survey that did not include the color-picking test. Therefore, the color-picking task likely provided the predisposed "borderline non-synesthetes" with an opportunity to dwell on their tendency toward synesthesia and allowed their subconscious sensations to become conscious ones. The finding suggests that the general population has a continuum of synesthetic disposition that encompasses both synesthetes and non-synesthetes.