  According to another line of objection, Martin is wrong to propose that being introspectively indiscriminible from a genuine perception is a necessary condition for being a conscious perceptual experience. For although being introspectively indiscriminible from a genuine perception may be a condition satisfied by all genuine perceptions and perfect hallucinations had by subjects capable of making introspective judgements about their perceptual experiences, it is not a condition that need be satisfied by other perceptual experiences. For instance, Siegel (2004) argues that experiences as of impossible scenes—e.g., experiences as of certain Escher scenes—do not satisfy this condition.