In this issue of Neuron, Seitz et al. show that humans exhibit enhanced perceptual discrimination for visual stimuli that have been repeatedly paired with reward under conditions of suppressed awareness. These findings challenge the view that awareness and focused attention are necessary for perceptual learning.

Suppose you have a large volume of an ordinary gas and you examined a small subvolume within it that contains a mean number of particles N. You would expect that the variance of that number, δN2, resulting from repeated measurements, is also equal to N. By “ordinary,” I mean two things. First, the gas is ideal, i.e., composed of particles with negligible interactions, and second, the gas is “cl...