Binocular disparity-based learning does not generalize to the other visual hemifield

Visual perceptual learning refers to long-lasting performance improvements on a visual skill, an ability presumably supported by plastic changes in early visual brain areas. Visual perceptual learning has been shown to be induced by training and to benefit from consolidation during sleep, presumably via the reactivation of learning-associated neuronal firing patterns. However, previous studies have almost exclusively relied on a single paradigm, the texture discrimination task, on which performance improvements may not rely on strictly perceptual skills. Here, we tested whether sleep has beneficial effects on a visual disparity discrimination task. We confirm previous findings in showing that the ability to discriminate different disparities is unaffected by sleep during a 12-hour retention period after training. Importantly, we extend these results by providing evidence against an effect of sleep on the generalization of improved disparity discrimination across the vertical meridian. We further rule out carry-over effects as a possible confound in our earlier within-subject study by relying on a between-subject design. The combined data from both studies argue against sleep as an important factor in the consolidation of a strictly perceptual skill. This sets important constraints on models of the role of sleep and sleep-associated neural reactivation in the consolidation of non-declarative memories.