A novel model of divergent perception
Our model predicts divergent perception based on different characteristics of synaesthesia and psychosis, and imagery extremes (aphantasia/hyperphantasia).
This model is currently being developed. You can watch a video explaining the model in detail at the link above!
Low confidence in sensory evidence leads to an over-reliance on high-level priors and insufficient prediction error updating based on incoming sensory stimulation (or the lack thereof), which can result in symptoms of psychosis such as hallucinations and delusions (Corlett et al., 2019).
High confidence in sensory evidence may result in strong low-level priors and enhanced perceptual abilities, such as in synaesthesia (van Leeuwen et al., 2020), although this may also be associated with perceptual hypersensitivity (van Leeuwen et al., 2019).
Mental imagery determines the sensory quality of divergent experiences, and may be used to (over- or under-) interpret ambiguous sensory information: people with extremely vivid imagery (hyperphantasia) likely overinterpret this information, and people with a complete absence of visual imagery (aphantasia) likely underinterpret this information. This may explain the lower susceptibility to pseudo-hallucinations in aphantasia compared to imagery (Königsmark et al., 2021).
In this model, different weights of priors and sensory evidence contribute to divergent perception. Confidence in Sensory input (S: purple dot) is positively related to Low-level (stimulus regularities) prior strength (L: green dot) and negatively related to high-level (beliefs) prior strength (H: blue dot). Mental imagery is considered an independent, mid-level interpretative prior (M: orange dot) that determines the sensory richness of mental representations. This schematic shows predicted likelihood of experiencing simple or complex pseudo-hallucinations during Ganzflicker stimulation.
Mental healthcare in aphantasia
A critical problem that bears further scrutiny is the combination of aphantasia and mental health challenges. Individuals struggling with their mental health require prompt diagnosis and empathetic early intervention to achieve the best outcome, but both of these needs present potential difficulties due to differences between aphants and imagers. Unhelpful or destructive mental imagery is considered a core symptom of various psychiatric disorders, such as Obsessive Compulsive Disorder (OCD; Moritz, Claussen, et al., 2014), Post-Traumatic Stress Disorder (PTSD) and other anxiety disorders (Hirsch & Holmes, 2007), eating and body dysmorphic disorders (Kadriu et al., 2019), depression (Moritz, Hörmann, et al., 2014; Weßlau et al., 2015), schizophrenia (Benson & Park, 2013; Brébion et al., 2008; Ji et al., 2019; Maróthi & Kéri, 2018), and bipolar disorder (Di Simplicio et al., 2016), among many others. In addition to the overt mental imagery present in those conditions, a lack of mental imagery is a symptom of both dementia (Ji et al., 2019) and prosopagnosia (Grüter et al., 2009). Having aphantasia may increase the potential for missed or misdiagnosis, as many medical and clinical professionals remain unaware of aphantasia as part of the spectrum of imagery within a healthy population.
The challenge of diagnosis is further compounded by the treatment protocols for these mental health conditions. The most common psychotherapeutic intervention as recommended by a large evidence base (Pilling et al., 2011), is Cognitive Behavioral Therapy (CBT). While CBT claims to be a functional approach, and should have no overt connection to imagery, an examination of the manuals reveals a recurring reliance on imagery-based approaches (Hofmann et al., 2012). Therefore, even if aphants with a mental health condition receive a correct diagnosis, the dominant therapeutic interventions used to treat these disorders are likely ineffective for them.
We are currently planning a mixed methods study using questionnaires and interviews to investigate the influence of aphantasia on mental healthcare evaluation, diagnosis, and treatment.
Mental imagery "extremes"
Visual mental imagery is the mental simulation of visual sensory information. In the past few years, it has come to light that many people have a "blind mind's eye" (aphantasia; Zeman et al., 2020), or the absence of visual mental imagery. A more widely explored phenomenon is extremely vivid visual imagery, now called "hyperphantasia". Not a lot is known about the behavioral and neural differences between people with aphantasia and hyperphantasia, or people with mental imagery extremes and "typical" mental imagery. In my research, I am currently exploring behavioral differences across the mental imagery spectrum. I am also investigating new techniques for classifying individuals who believe they have aphantasia or hyperphantasia -- moving away from the VVIQ as a "diagnostic" tool (see McKelvie, 1995). This research is ongoing and updates will be posted to my website in time!
Previous studies have proposed a link between modal imagery vividness and hallucination proneness in pathology (Aleman et al., 2000; Aleman & de Haan, 2004). Exploring the relationship between visual imagery and anomalous perception in normative samples (in the absence of pathology) will provide much-needed insight about top-down factors that contribute to hallucinatory experience. My research therefore focuses on inducing pseudo-hallucinatory experiences using visual noise (pareidolia) and visual flicker (Ganzflicker) paradigms. Currently, I am interested in individual differences in the likelihood to experience vivid and complex pseudo-hallucinations in people with different visual imagery abilities, such as aphantasia.
A breakdown of the likelihood to experience NO pseudo-hallucinations across different imagery vividness ratings from 0 (complete aphantasia) to 10 (extremely vivid imagery), shown in gray. A logistic regression line in blue indicates the probability of seeing PH: about 60% probability for aphants and about 90% probability for people with vivid imagery. Individual data points (blue dots, jittered) indicate the distribution of individuals who saw pseudo-hallucinations (above the bars) and those who did not see pseudo-hallucinations (underneath the bars). In summary, individuals who report having even a little bit of visual imagery are just as likely to see pseudo-hallucinations in Ganzflicker as those with moderate and vivid imagery. Individuals with complete aphantasia, on the other hand, are much less likely to experience pseudo-hallucinations at all. N=1,810.