Synesthesia is a condition where presentation of one perceptual class consistently evokes additional experiences in different perceptual categories. Synesthesia is widely considered a congenital condition, although an alternative view is that it is underpinned by repeated exposure to combined perceptual features at key developmental stages. Here we explore the potential for repeated associative learning to shape and engender synesthetic experiences. Non-synesthetic adult participants engaged in an extensive training regime that involved adaptive memory and reading tasks, designed to reinforce 13 specific letter-color associations. Following training, subjects exhibited a range of standard behavioral and physiological markers for grapheme-color synesthesia; crucially, most also described perceiving color experiences for achromatic letters, inside and outside the lab, where such experiences are usually considered the hallmark of genuine synesthetes. Collectively our results are consistent with developmental accounts of synesthesia and illuminate a previously unsuspected potential for new learning to shape perceptual experience, even in adulthood.

In comparison to studies suggesting that normoglycemia is an easily achievable goal, our protocol often recorded glucose values <80 mg/dL, although values <60 mg/dL were rare and usually due to protocol violations. In the interval before automated glucose-sensing insulin infusion devices become available for the intensive care unit, the current protocol is available to assist others in achieving target glucose levels shown to improve mortality rate in an intensive care unit population.