Narrowing the gap between analytically convenient and naturalistic stimuli.

The gulf between mathematically motivated stimuli-such as sine waves and noise ensembles-and images drawn from natural scenes may not be as wide as it appears. For the former, the mathematical properties that support their utility as analytic probes are explicit. For naturalistic stimuli, this is not the case, but they are created by physical processes whose outcomes-at least in principle-heavily constrain their statistics. Images generated computationally occupy a middle ground: Their mathematical properties remain implicit in the rules that generate them, but these rules are simpler than the processes that generate natural images. It is suggested that a greater understanding of the statistics of natural images, while challenging, will enhance their utility as experimental tools and thereby lead to new insights into the design principles of sensory systems.