Telepathy, and Elves who refuse the summons to Mandos -- Reading Material

Parma Eldalamberon xvii, (Root) PHAN- continues:

The High Elves distinguished clearly between fanar, the 'physical' raiment adopted by the Spirits in self-incarnation, as a mode of communication with the Incarnates, and other modes of communication between minds, that might take 'visual' forms.

They held that a superior 'mind' by nature, or one exerting itself to its full in some extremity of need, could communicate a desired 'vision' direct to another mind. The receiving mind would translate this impulse into the terms familiar to it from its use of the physical organs of sight (and hearing) and project it, seeing it as something external. It thus much resembled a fana, except that in most cases, especially those concerned with minds of less power (either as communicators or receivers) it would frequently be less vivid, clear, or detailed, and might even be vague or dim or appear half-transparent. These 'visions' were in Quenya called indemmar 'mind-pictures'. Men were receptive of them. According to records of the time, mostly when presented to them by the Elves. To receive them from another human being required a special urgency of occasion, and a close connexion of kinship, anxiety or love between the two minds.

In any case indemmar were by Men mostly received in sleep (dream). If received when bodily awake they were usually vague and phantom-like (and often caused fear); but if they were clear and vivid, as the indemmar induced by the Elves might be, they were apt to mislead Men into taking them as 'real' things beheld by normal sight. Though this deceit was never intentional on the part of the Elves, it was often by them believed to be.

[Footnote: ] The matter of corrupted or malicious elvish beings is elsewhere considered. According to the Elves these were mainly disembodies Elves, who had met with some mortal damage, but rebelled against the summons to their spirits to go to their place of Awaiting. Those who so rebelled were mostly those who had been slain in the course of some wrong-doing. Thus they wandered as 'houseless' elf-souls, invisible except in the form of indemmar that they could induce in others, and filled often with malice and envy of the 'living', whether elvish or human.