The Ajna is symbolised by a sacred lotus with two petals, and corresponds to the colours violet, indigo or deep blue, though it is traditionally described as white. It is at this point that the two sides Nadi Ida (yoga) and Pingala are said to terminate and merge with the central channel Sushumna, signifying the end of duality, the characteristic of being dual (e.g. "light" and "dark", or "male" and "female"). The seed syllable for this chakra is the syllable OM, and the presiding deity is Ardhanarishvara, who is a half male, half female Shiva/Shakti. The Shakti goddess of Ajna is called Hakini. In metaphysics, Bindu is considered the dot or point at which creation begins and may become unity. It is also described as "the sacred symbol of the cosmos in its unmanifested state". Bindu is the point around which the mandala is created, representing the universe. Ajna (along with Bindu), is known as the third eye chakra and is linked to the pineal gland which may inform a model of its envisioning. The pineal gland is a light sensitive gland that produces the hormone melatonin which regulates sleep and waking up, and is also postulated to be the production site of the psychedelic dimethyltryptamine, the only known hallucinogen endogenous to the human body. Ajna's key issues involve balancing the higher and lower selves and trusting inner guidance. Ajna's inner aspect relates to the access of intuition. Mentally, Ajna deals with visual consciousness. Emotionally, Ajna deals with clarity on an intuitive level.