Otzar ha-Geonim, ed. B. Lewin, vol. 1: Tractate Berakhot (Jerusalem, 1931), Appendix, p. 3.

Jewish Mysticism
The Holy One, blessed be He, makes His glory visible to those who fear Him and His pious ones through an understanding of the heart in the image of an anthropos sitting, as it is written, “I saw the Lord seated upon His throne, with all the host of heaven standing to His right and left” (1 Kings 22-19), and it is written, “I saw God sitting on the high and lofty throne and the skirts of His robe filled the Temple” (Isa. 6-1). [The glory appears] as one that has feet, as it is written, “[They saw the God of Israel] and under His feet there was the likeness of a pavement of sapphire” (Exod. 24-10). It is clear to us that the vision spoken of here is a vision of the heart (re’iyat ha-lev) and not vision of the eye (re’iyat ha-‘ayin). It is impossible to say that an image (demut) of God is seen through a vision of the eye… It is possible to say that one sees through a vision of the heart the image of the glory (demut kavod) but not through an actual vision of the eye, for the verse states explicitly, “When I spoke to the prophets and spoke parables through the prophets,” u-ve-yad ha-nevi’im ’adammeh (Hosea 12-11). This indicates that [God] showed to every prophet an image (dimyon) that he could see.

Translated by Elliot Wolfson in Through a Speculum that Shines- Vision and Imagination in Medieval Jewish Mysticism, Princeton- Princeton University Press, 1994.