Double blind session
A double blind session is considered to be one where "double-blind tasking" is used (see "double blind tasking"). That is where neither the viewer nor the monitor know what the target is. The hope is that the monitor will not pollute the session with his/her knowledge of the target.
In reality, it rarely, if ever works, and then only with the most highly trained monitors. Once the viewer has given two or three descriptions, the monitor will almost certainly form a mental image of what he thinks the target might be, and from that point on, the pollution and leading exist, whether the monitor has knowledge of the real target or not.
Double-blind sessions are required in the laboratory (research mode)for experimental purity.
In training mode, double-blind sessions are not desirable, simply because allowing the monitor to know what the target is allows him/her to study the viewer's reactions to the various parts of the target, and the monitor thereby "learns the viewer".
In practice mode, sessions should start single blind, but as the monitor learns the viewer, the monitor should be weaned slowly of target knowledge in order to train the monitor to depend on the viewer's physical actions rather than the viewer's words.
In actual applications work (operational mode), the need for double blind conditions is not so great, and may at times even slow the session down by allowing the viewer to fixate on a part of the target site which is of no importance to the customer, or ruin it altogether, as the monitor's pollution leads the viewer to find an incorrect target.