The neurotransmitter acetylcholine (ACh) has been extensively studied at the level of synapses and neural circuits, but comparatively little is known about its effects on perception and cognition in humans. We augmented the effects of ACh in the brains of healthy human participants by administering the cholinesterase inhibitor donepezil (trade name: Aricept). I will describe the effects of increased cholinergic function on perceptual learning, visual spatial attention, and encoding of stimulus information in visual cortex. Our results demonstrate that pharmacological enhancement of cholinergic transmission produces many of the same effects as allocation of voluntary attention, including facilitating perceptual learning and increasing the selectivity of visual cortical responses to visual stimuli.