© 2017 by De Gruyter. Neuroscientific research has made tremendous progress towards unravelling the neuronal codes that underlie our rich sensory perception and experience. From single neurons in primates' visual brain that predict perceptual choices to activity patterns in defined neuronal circuits, electrical activity across different levels correlates with perception. The key to how neuronal signals give rise to our visual experience lies in causal interventions directly applied to neurons and circuits, interventions that alter perception naturalistically and in predictable ways. The most powerful and reliable intervention method in primates remains invasive electrical micro-stimulation, which can change selectively the appearance of visual objects defined by more than one visual cue. Such artificial signals are integrated with visually evoked stimuli and with contextual factors like reward. Scaling up these methodologies presents opportunities for vision replacement through cortical neuro-prosthetics.