Clairvoyants use what is called the third eye, which is related to the pineal gland and the psychic chakra, located between the eyebrows. This chakra is known as the mind’s eye, because it allows you to peer into the subconscious thoughts and feelings of yourself or another person. Anyone can open up their third eye; this process involves meditation, introspection, and will increase intuition when used regularly.
Some psychic spells can be undercast. This means that the spellcaster can cast the spell at the level that he knows, or as any lower-level version of that spell, using the appropriate spell slot. When a spellcaster undercasts a spell, it is treated exactly like the lower-level version, including when determining its effect, saving throw, and other variables. For example, a psychic spellcaster who adds ego whip III to his list of spells known can cast it as ego whip I, II, or III. If he casts it as ego whip I, it is treated in all ways as that spell; it uses the text and the saving throw DC for that spell, and requires him to expend a 3rd-level spell slot.