Abstract
The human visual system is obviously generative: most humans can and do generate imagery in the absence of retinal stimulation, and the internal generation of imagery clearly engages the entire visual cortex. However, we know very little about what the brain does with its ability to generate images. We will consider the hypothesis that the ability of visual cortex to generate imagery is a consequence of housing a generative model of the world that is needed to see. We will present empirical evidence from mental imagery experiments that imagery and vision rely upon the same generative model to make inferences that are conditioned on unseen and seen data, respectively. We will then consider evidence for the alternate hypothesis that generativity is not for seeing, and may even obstruct seeing. According to this hypothesis, non-visual systems may route their process-specific variables through the visual cortex to non-visual solve tasks. These extra-visual inputs may evoke visual imagery, and may even use visual imagery, while contributing nothing to or even obstructing seeing. We review evidence from the animal literature that appears to support this view, and propose several novel experiments to adjudicate between the two hypotheses.