Fallen behind on reading PDML yet again, but wanted to share a URL I tripped over. Apparently human eyes _are_ sensitive to near-IR, just not very much so. This page describes wandring around wearing welder's goggles with IR filters in them so that one's eyes get accustomed to the low levels of light (relative to the retina's sensitivity at those wavelengths); what the author describes seeing matches the results of shooting Kodak HIE with a filter (except for the red tint to everything).
-- Glenn