Background
Hallucinations are a core feature of psychosis, often causing considerable distress. Reported prevalence ranges from 70% for auditory hallucinations (AHs) to 30% for visual hallucinations (VHs) and 4% for hallucinations in the tactile domain. AHs have been studied extensively but studies on VHs are scarce. The current study investigated the phenomenology of VHs and AHs in the realm of daily life, by analyzing their prevalence, course and co-occurrence over a 6-day period and their temporal relation to emotions and delusions.
Methods
The ESM, a structured diary technique, was used to investigate hallucinatory experiences in the context of daily life in a pooled data-set of 184 participants (71% males) with psychosis spectrum disorders, which were recruited from mental health facilities in the south of the Netherlands and Belgium. All self-assessments were rated on 7-point Likert scales. VHs were defined using participants' scores on the item “I see phenomena”. AHs were measured using the item “I hear voices”.
Results
Overall, 73 participants (40%) reported hallucinations. Ten participants reported VHs only, 38 reported both VHs and AHs, and 25 participants reported AHs only. AHs co-occurred with VHs in 40% of the hallucinatory moments. Patients with both VHs and AHs reported higher levels of negative affect, lower levels of positive affect and higher delusional intensity than non-hallucinating patients. Increased delusional intensity preceded the onset of hallucinatory episodes, whereas increases in positive or negative affect did not.
Discussion
These results show that VHs are common in patients with psychosis spectrum disorders and often co-occur with AHs in time. Furthermore delusional ideation may precede hallucinatory episodes in the realm of daily life, rather than result from a hallucination and affective dysregulation might not play a primary role in hallucination onset.
Hallucinations are considered core symptoms of psychosis spectrum disorders and can appear in all sensory modalities (e.g. olfactory, tactile), but are in patients most frequently experienced in the auditory and visual modalities. Auditory hallucinations (AHs) in psychosis typically involve voices, ranging from single words or short phrases to multiple voices conversing or commenting on the voice hearer, and affect about 70% of schizophrenia patients during the illness course (WHO, 1973 and Baethge et al., 2005). Visual hallucinations (VHs) also involve a wide range of experiences, such as seeing dots, figures or people, with lifetime prevalence rates up to 56% (Bracha et al., 1989 and Baethge et al., 2005). Despite the many patients with a psychotic disorder being affected by hallucinations, we know disappointingly little about the prevalence of AHs and VHs and information on the regulation of these experiences is limited. Questions such as ‘What is the real life prevalence rate of AH and VH and how often do they co-occur?’, ‘Do hallucinations fluctuate in intensity and what drives these fluctuations?’ seem crucially important from a clinical point of view; still they remain largely unanswered.
One study, using the Experience Sampling Method (a structured daily diary method), found that 65% of patients with schizophrenia reported unusual visual phenomena and 49% reported auditory phenomena during the course of a week (Delespaul et al., 2002). This study also showed marked variability in hallucinatory intensity over periods of hours and days, both in AHs and VHs. An interview study found significant comorbidity of AHs and VHs, with 70% of patients suffering from VHs also reporting AHs (Gauntlett-Gilbert and Kuipers, 2003).
It is possible that affective processes play a role in triggering hallucinatory phenomena. Patients retrospectively recall affect to be a relevant factor in the onset of a hallucination (Gauntlett-Gilbert and Kuipers, 2005) and report elevated levels of distress and anxiety while hallucinating (Honig et al., 1998 and Delespaul et al., 2002). It remains unclear, however, whether changes in emotion precede the onset of hallucinatory experiences in everyday life and if so, whether this is equally true for auditory and visual hallucinations.
It is also possible that delusional thinking plays a role in the onset of hallucinations. Early theorists argued that delusions are rational attempts to interpret anomalous experiences, hence that hallucinations drive delusional thinking (Maher, 1974). Indeed, the presence of delusions has found to be strongly associated to the presence of hallucinations (Liddle and Barnes, 1990 and van Os et al., 2000). Furthermore, several epidemiological studies have shown that hallucinatory experiences followed by a delusional interpretation increase the risk to develop a clinical psychosis (Krabbendam and van Os, 2005 and Smeets et al., 2010). However, alternatively, delusional beliefs may affect the salience of inner experiences (Kapur, 2003) and the source-monitoring mechanisms involved in the development of a hallucination (Bentall, 1990, Morrison and Haddock, 1997 and van 't Wout et al., 2004).
In order to advance our knowledge of factors triggering the emergence of hallucinations and about the relationships between hallucinations, emotions and delusional thoughts, we used the Experience Sampling Method (ESM) to study VHs and AHs in a large group of patients with a psychotic disorder. ESM is a structured self-assessment technique in which participants are prompted at random intervals throughout the day to report their current experiences (Myin-Germeys et al., 2009). This method allows the investigation of hallucinations, delusions and emotional experience in the moment, in the context of the normal daily life of patients without making a strong appeal to memory. ESM has been proven to be valid and feasible to study positive psychotic symptoms and their association with emotions and daily life stress (for a review see Oorschot et al., 2009). In a sample of 184 patients with psychotic disorder, we examined (i) the prevalence and course of VHs and AHs over a 6-day period, (ii) the co-occurrence of VHs and AHs in normal daily life, and (iii) the temporal association between VHs/AHs and emotional and delusional experiences.
