Descartes, Rene - Why some people are unable to conceive of the existence of a spiritual realm
Type of Spiritual Experience
Also an interesting comment on the negative effects that imagination can have if you are very 'materialistic'
A description of the experience
Rene Descartes – Key Philosophical Writings
What causes many, however, to persuade themselves that there is difficulty in knowing this truth.... is the fact that they never raise their minds above the things of sense, or that they are so accustomed to consider nothing excepting by imagining it, which is a mode of thought especially adapted to material objects, that all that is not capable of being imagined appears to them not to be intelligible at all......