Perceptual learning refers to long-lasting improvement in the performance of a perceptual discrimination through training that is specific to the stimuli used for training. It is used as a laboratory model to better understand the processes by which people learn new and intricate skills throughout the lifespan.
Cholinergic enhancement of perceptual learning
We have administered the cholinesterase inhibitor and Alzheimer’s medication donepezil (see Cholinergic pharmacology section) to healthy human subjects while they were undergoing perceptual learning of motion direction discrimination. This cholinergic enhancement increased the magnitude and specificity of perceptual learning (Rokem and Silver, 2010). A follow-up study with the same subjects showed that both the effects of perceptual learning on motion direction discrimination and the beneficial effects of donepezil on perceptual learning persisted for at least several months after the end of training and drug administration (Rokem and Silver, 2013).
These results suggest that cholinergic enhancement with donepezil could be used to augment perceptual learning procedures that are used to treat patients with amblyopia. Amblyopia refers to visual impairment in adults that is caused by abnormal visual experience in childhood. In collaboration with Dennis Levi’s and Susana Chung’s laboratories, we tested whether administration of donepezil during perceptual learning treatment could facilitate the recovery of vision in patients with amblyopia. Our first pilot study did not provide evidence that cholinergic enhancement benefited perceptual learning of letter identification tasks in amblyopia (Chung et al., 2017), and a second study in participants with normal vision also found no detectable effect of donepezil on perceptual learning of letter identification in peripheral vision (Levi et al., 2020).
One difference among the studies described above is the nature of the task used for perceptual learning (a motion direction discrimination task showed strong effects of cholinergic enhancement on perceptual learning; letter identification tasks did not). We also found no measurable effect of cholinergic enhancement with donepezil on perceptual learning of visual texture discrimination (Byrne et al., 2020). We are currently examining whether differences between the visual processing streams that are most relevant for a given task (dorsal stream for motion; ventral stream for letter identification and texture discrimination) can account for different effects of cholinergic enhancement in perceptual learning.
Perceptual learning and sleep
Our finding that training under donepezil increases perceptual learning may reflect a higher fidelity of neural representations of the stimuli used for training (Silver et al. 2008; see also Cholinergic pharmacology section). However, acetycholine also plays critical roles in consolidation of memories during sleep. In collaboration with Sara Mednick’s lab, we discovered sex differences in the role of sleep in perceptual learning of motion direction discrimination (McDevitt et al., 2014). Men who napped after a single session of training exhibited more learning than men who did not nap, and the perceptual learning was specific to the trained direction of motion in both groups of men. In contrast, women in both nap and no-nap groups showed significant learning of both trained and untrained directions of motion.