<prompt> Which of the following is not a feature of hallucination: September2010It can occur in any sensory modalityIt is independent of will of observerIt is defined as perception occurring without external stimulationAlways pathological  <response>: Ans. D: Always pathologicalA hallucination, in the broadest sense of the word, is a perception in the absence of a stimulus.In a stricter sense, hallucinations are defined as perceptions in a conscious and awake state in the absence of external stimuli which have qualities of real perception, in that they are vivid, substantial, and located in external objective space. Hallucinations can occur in any sensory modality -- visual, auditory, olfactory, gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, thermoceptive and chronoceptive. 