Define 'psychotic symptom' and 'unusual perceptual experience', and outline the main differences between them.

Psychotic symptoms and unusual perceptual experiences (UPEs) are generally considered to be two dichotomous phenomena. Psychotic symptoms are characterised by hallucinations (perception of stimuli that does not exist) and/or delusions (beliefs maintained despite being contradicted by reality) (Ho, Andreasen, Flaum, Nopoulos & Miller, 2000). Perception is defined as the organisation, identification and interpretation of sensory stimuli to process the environment, though this can manifest as UPEs whereby individuals interpret stimuli incorrectly, thus resulting in distortions (Raine et al., 1994).
The two phenomena are distinguished with psychotic symptoms being more severe, frequent, distressing and characteristic of psychological disorders (Daalman et al., 2010; Luhrmann et al., 2015; Posey & Losch, 1983). Individuals experiencing these symptoms additionally have difficulties with cognitive inhibition (Waters et al., 2003), deficits in source memory (Badcock et al., 2008; Chhabra et al., 2011) and fundamental structural differences in the brain (Allen et al., 2008). In comparison, UPEs are commonly experienced in isolation among the general population and considered relatively harmless (Escher, Romme, Buiks, Delespaul & van Os, 2002; Rose & Barker, 1978). It is important to note that these distinctions appear to be on a spectrum of severity, rather than qualitatively different dissimilarities.