Testosterone induces off-line perceptual learning.

RATIONALE: Perceptual learning operates on distinct timescales. How different neuromodulatory systems impact on learning across these different timescales is poorly understood. OBJECTIVES: Here, we test the causal impact of a novel influence on perceptual learning, the androgen hormone testosterone, across distinct timescales. METHODS: In a double-blind, placebo- controlled, cross-over study with testosterone, subjects undertook a simple contrast detection task during training sessions on two separate days. RESULTS: On placebo, there was no learning either within training sessions or between days, except for a fast, rapidly saturating, improvement early on each testing day. However, testosterone caused "off-line" learning, with no learning seen within training sessions, but a marked performance improvement over the days between sessions. This testosterone-induced learning occurred in the absence of changes in subjective confidence or introspective accuracy. CONCLUSIONS: Our findings show that testosterone influences perceptual learning on a timescale consistent with an influence on "off-line" consolidation processes.