"A hallucination is a percept experienced in the absence of an external stimulus to the corresponding sense organ" - Oxford textbook of psychiatry
Jaspers suggested the following defnition 'a false perception which is not a sensory
distortion or a misinterpretation, but which occurs at the same time as real
You are having a visual hallucination when there is no external object, but you are still percieving that there is an object. Visual hallucinations are seen in some psychiatric illness.Recently i came across this interesting image in Scientific American. Its called the Yorick's Skull. This was the image.
The site says, 'To experience a vintage afterimage illusion, stare at the X in Yorick’s left eye socket for about 30 seconds. Then look away at a wall or piece of paper, and you will see a ghostly apparition.'
When we stare at a wall after seeing the image, there is no external object. But we are still able to percieve the image of the ghost. So is this an illusion?? or is it that we are hallucinating??