Original sentence: It is not widely recognised that hallucinatory experiences are not merely the prerogative of the insane, or normal people in abnormal states, but that they occur spontaneously in a significant proportion of the normal population, when in good health and not undergoing particular stress or other abnormal circumstance
Edited sentence: It is not yet widely recognised that hallucinatory experiences are not merely the prerogative of the insane, or normal people in abnormal states, but that they occur spontaneously in a significant proportion of the normal population, when in good health and not undergoing particular stress or other abnormal circumstance