There are reasons they dont work and recommendations to make them effective.
One of the reasons they dont work is related to the sleep process. As you fall asleep your sensory acuity is dampened and you are less sensitive to sensory stimulation – including audio.
The recommendation is also related to the sleep process. As you fall asleep you transition from a waking state through a hypnoidal state and then onto deeper sleep. As your senses are dampened; so is your critical mind. This is ripe time to make suggestion and according to the sleep cycle this is about 30 minutes after youve fallen asleep.
Therefore the tape must start about 30 mins after you play it.
