Psychotic symptoms (hallucinations and delusions) are present in several psychiatric and neurological disorders as well as in the general population. Effective treatment strategies for these symptoms in all patients are lacking and treatment-response can presently not be predicted. To date, the exact pathophysiological mechanism of these symptoms remains unknown. By investigating (subtypes) of hallucinations and delusions in all populations, a common pathway may be found, leading to more effective treatment options. Alternatively, different subtypes may be associated with different pathophysiological mechanisms.

Inclusion Criteria:

• age > 18 years
• mentally competent
• in case of delirium: family member able to give informed consent
• Individuals with hallucinations will have to experience at least one episode of hallucinations over the last month.
• Individuals without hallucinations: no current hallucinations and a history of maximum 1 episode of hallucinations with a maximum duration of 1 week, at least two years ago.

Exclusion Criteria:

• Age <18)
• Participants that cannot read, speak or understand Dutch
• For all included diagnostic groups except delirium: Mentally incompetent individuals who are not capable to provide informed consent, as determined by their treating physician.

We aim to include subjects of each of the following diagnostic groups, both with and without psychotic symptoms:

1. patients with schizophrenia spectrum disorders
2. patients with borderline personality disorder (BPD)
3. patients with hearing impairment
4. patients with visual loss
5. patients with Parkinson's disease (PD)
6. patients with Alzheimer's disease (AD)
7. patients with Lewy Body dementia (DLB)
8. patients with post-traumatic stress disorder (PTSD)
9. patients with delirium
10. healthy individuals
11. patients with mood disorder