5th November 2023

Psychopathology of Perception

Sensory System, Sensation and Perception

Before we talk about perceptual abnormalities, which is one of the most fascinating aspects of psychiatry, let’s discuss the key concepts of sensation and perception. Although sensation and perception are interrelated processes, they are distinct from one another.

Sensation is the initial stage of receiving information from the external world, which involves sensory receptors receiving information and transmitting it to the brain in the form of neural impulses. Sensation results in raw information from the senses.

Perception, on the other hand, is the process of interpreting the information received by the sensory process at the cortical level. As a result, we interpret and give meaning to the information received. This is an active process that involves constructing a representation of the external world using our own internal templates.

Perception is influenced by a range of factors, such as attention, context, prior experiences, memory, cultural expectations, and pre-existing concepts.

To highlight the difference between sensation and perception, we can look into the example of visual object agnosia. In this condition, an individual may still have intact sensory functions and be able to detect the presence of an object in their visual field (intact sensation), but they are unable to identify or recognise the object or understand its function or meaning (impaired perception).

Sensory system includes:

• Visual
• Auditory
• Tactile
• Olfactory
• Gustatory
• Kinaesthetic
• Proprioceptive pathways

References

• Oyebode, F. (2015). Sims’ Symptoms in the Mind. Textbook of Descriptive Psychopathology. Elsevier: 5th Ed.

Mental Imagery

Imagery can be described as the internal mental representation of the world that is actively drawn from memory. It is distinct from perception because it does not involve any external stimulus or the perception of an actual object, but rather, it is essentially a product of our imagination or fantasy. Imagery involves voluntary production of images with full awareness that they are mental and not external phenomena. When you think about your favourite meal and try to remember all the details, the texture, the colours, the taste, this is an example of mental imagery.

In his book General Psychopathology, Karl Jaspers argued that images are not just simple representations of external objects or events, but rather, they are subjective constructions that are influenced by our individual experiences and perspectives. According to Jaspers, images can take many forms, including not only visual representations but also sounds, smells, and other sensory experiences.

Jaspers described the formal characteristics of images as follows:

• Images are figurative and have a character of subjectivity
• They appear in inner subjective space.
• They are not clearly delineated and come before us incomplete.
• Although sensory elements are individually equal to those in perception, they are mostly insufficient.
• Images dissipate and always have to be recreated.
• Images are actively created and are dependent on our will.

Images of obsessional thinking

Although this topic of thinking isn’t commonly asked about in Paper A, it is added here to enhance the understanding of imagery and emphasise how complicated it actually is to try to define these phenomena that are fundamentally introspective. Although the description by Jaspers is an admirable attempt to do so, you will realise that in abnormal imagery, some of the qualities might be different than described.

In contrast to normal mental imagery, the images of obsessional thinking may be quite vivid and could be experienced involuntarily.

These images have been considered by De Silva (1986) to be one of the following four types:

1. The obsessional image depicts repetitively the unwanted intrusive cognition – Images of blood flowing, injuries, etc…
2. The compulsive image depicts compulsive behaviour by rectifying either an obsessional image – The woman who saw corpses in coffins and had to imagine the same people standing – or an independent compulsive image.
3. The disaster image affects compulsive checkers who may not only fear that disaster will occur unless they check but also ‘see’ the disaster happening in fantasy – The house burning down if the gas taps are not turned off.
4. The disruptive image may intrude while compulsive rituals are being carried out and necessitate the ritual being recommenced.

Eidetic imagery

Also known as photographic memory, is a rare phenomenon in which an individual can vividly recall visual details of an object or scene with great clarity and detail, even after only a brief exposure to it.

Eidetic imagery:

• Is more commonly observed in children and tends to decline as they grow older.
• May be part of religious experiences.
• Not associated with any specific psychopathology.

References

• de Silva, P. (1986). Obsessional-compulsive imagery. Behaviour Research and Therapy, 24(3), 333–350. doi:10.1016/0005-7967(86)90193-2
• Jaspers, K. (1997). General psychopathology: Volume 1 (J. Hoenig & M. W. Hamilton, Trans.). Baltimore, MD: Johns Hopkins University Press.
• Oyebode, F. (2018). Sims’ symptoms in the mind: Textbook of descriptive psychopathology(6th ed.). London, England: Elsevier Health Sciences.

Perceptual Abnormalities

In this topic, we will explore perceptual abnormalities in two headings.

Sensory distortion – The object is perceived in a distorted way; however, it is still recognised as what it is.

False perception – A new perception occurs that may or may not be in response to an external stimulus.

Sensory distortions

Sensory distortions are changes in perception where a real perceptual object is perceived in a distorted way. This distortion can involve any of the components of perception, such as size, shape, colour, motion, general quality, and uniqueness.

In sensory distortions, the object is correctly recognised and identified. However, there is a deviation from its customary appearance.

Distortions in visual perception

Size and proportions

Dysmegalopsia refers to a change in the perceived shape of the object and includes micropsia and macropsia.

Macropsia – The object is perceived to be larger than expected.

Micropsia – The object is perceived to be smaller than expected.

Hemimicropsia – Apparent reduction in hemifield of vision.

Metamorphopsia – Alteration of the customary shape; object appears warped, distorted.

When metamorphopsia affects faces, it’s referred to as paraprosopia.

Occasionally, dysmegalopsia may occur in poisonings (atropine, hyoscine); however, it is more common in central lesions, mainly affecting the posterior temporal lobe. In temporal lobe epilepsy, these distortions may occur during the aura or the seizure itself.

Colour

Visual hyperaesthesia describes when the actual hue and quality of colour are affected.

Dyschromatopsia – Perversion of colour perception, usually associated with unilateral posterior lesions.

Achromatopsia – Complete absence of colour described after unilateral or bilateral occipital lesions, usually of the lingual and fusiform gyri.

Visual hyperaesthesias can be associated with LSD, MDMA, mania or epileptic auras.

Spacial location

Teleopsia – Object appears further away than it should.

Pelopsia – Object appears nearer than it should.

Alloaesthesia – When the perceived object is in a different position from what is expected.

Other

Palinopsia – (Greek: palin for ‘again’ and opsia for ‘seeing’) is the persisting or recurring perceptual experiences of a visual image after the stimulus has been removed. It is often associated with organic causes.

Akinetopsia – Impairment of visual perception of motion (very rare).

Distortions in auditory perception

Palinacousis – The perseveration of auditory perception after the original sound has ceased. It can be seen as the auditory analogue of palinopsia. It is often associated with organic causes.

Hyperacousis – When ordinary noises sound abnormally loud. This may be the result of intense emotions or a lowering of the physiological threshold and can be seen in depression, migraine and some toxic states, for example, the hangover after acute alcohol excess.

Hypoacousis – Can occur in delirium, where the threshold of all senses is raised. The defect of attention found in delirium further reduces sensory acuity, and hypoacousis can be seen in other conditions where attention is impaired.

Distortions in tactile perception

Palinaptia – The experience of tactile sensation outlasting the stimulus so that an object held in the hand continues to be perceived well after it has been discarded.

Exosomesthesia – The ‘displacement of cutaneous sensation into extrapersonal space’.

False perceptions

In this chapter, we will talk about false perceptions or ‘perceptual deceptions’, which include illusions, hallucinations and pseudo-hallucinations.

Illusions

When stimuli from a perceived object are combined with a mental image to produce a false perception, this is called an illusion. In contrast to ‘sensory distortions’, where the perceptual object is still recognised and identified as it is, in illusions, the object is perceived as something else. In that sense, it can be described as a misinterpretation of sensation.

Although visual illusions are the most common ones, illusions can happen in any modality. Illusions in themselves don’t necessarily indicate any psychopathology, and they can be experienced by anyone.

There are three types of illusions that were defined: affect illusion, completion illusion and pareidolic illusion.

Affect illusion

Affect illusion refers to the phenomenon where the emotional state of a person can influence their perception of the world around them; this is particularly common for fear. If a person is feeling anxious, scared or threatened, they may perceive neutral or ambiguous stimuli as being threatening or dangerous. A typical example would be a child who is scared of the dark, mistaking a coat that is hanging on the door for a person in his room or a monster. Affect illusions are banished when close attention is given to the object if the emotional state of the person allows them to remain calm and focus on the object.

Completion illusion

Completion illusion occurs when our brain fills in missing information based on our expectations and past experiences. For example, multiple people might interpret an ambiguous or incomplete stimulus differently based on their individual backgrounds, expertise, or experiences. It demonstrates the principle of closure in Gestalt psychology: there is a human tendency to complete a familiar but not quite finished pattern. Completion illusions depend on inattention and are banished when close attention is given to the object.

Pareidolic illusion / pareidolia

Pareidolic illusions refer to vivid mental images occurring without conscious effort when perceiving ambiguous stimuli, for example, seeing shapes in clouds or human faces on tree trunks. Pareidolia occurs more commonly in children than adults and can be provoked with psychomimetic drugs.

It’s important to note that while completion and affect illusions occur during inattention and are banished by close attention, focusing on the object increases the intensity of pareidolic illusions as they become more intricate and detailed. It’s why once you perceive a pareidolic illusion, e.g. an animal in the clouds, it may be ‘hard to unsee’.

Hallucinations

There are multiple definitions of hallucinations by different authors:

• ‘Perceptions which arise in the absence of any external stimulus’ (Esquirol, 1833).
• ‘False perceptions that are not in any way distortions of real perceptions but spring up on their own as something quite new and occur simultaneously with and alongside real perception.’ (Jaspers, 1997).
• A hallucination is a perception without an object (within a realistic philosophic framework) or the appearance of an individual thing in the world without any corresponding material event (within a Kantian framework), according to Cutting (1997).

Aggernaes (1972) investigated the sense of reality that patients experience during hallucinations, and he built on the work of Rasmussen by identifying six qualities that are common to both normal sensations and hallucinations. These qualities were present in over 90% of the hallucinations that were studied.

• Normal sensation and hallucinations are both perceived as sensation and not as thought or fantasy.
• Both normal sensation and hallucinations have a quality of behavioural relevance.
• Normal sensation and hallucinations share a quality of objectivity, in that the observer feels that the same object could be experienced with another sense under different conditions.
• An object is considered to exist if the observer feels certain that it still exists, even if nobody else is experiencing it at that time. This quality is shared by both perceived objects and hallucinations.
• Both perceived objects and hallucinations are experienced involuntarily, and the observer feels that it is impossible or extremely difficult to dismiss the experience simply by wishing to do so.
• Normal perception and hallucination share a quality of independence, where the observer is aware or becomes aware through questioning that their experience is not simply the result of being in an unusual mental state.

However, another quality of normal object perception that was found to be frequently absent during hallucinations is the quality of publicness. This quality refers to the perception that anyone with normal sensory faculties would be able to perceive the same object. In many cases, the hallucinator does not believe that others could share their experience and may provide a delusional explanation for this.

Hallucinations can be elementary or complex. Elementary hallucinations are simple sensory experiences that are distorted or amplified versions of normal perceptions. They are usually limited to one sensory modality, such as vision, hearing, or touch. Examples of elementary hallucinations may include seeing flashes of light, hearing buzzing sounds, machinery sounds, a single tone, etc. Elementary hallucinations can be seen in acute organic states and also in prodromal psychosis.

Complex hallucinations include more sophisticated false perceptions, such as hearing ‘voices’ in the form of human speech, seeing complete images, etc.

Auditory hallucinations

‘Hearing voices’ is quite characteristic of schizophrenia, but it also occurs occasionally in other conditions, including but not limited to chronic alcoholic hallucinosis or affective psychoses. These voices are sometimes called phonemes (not to be confused with the same term used in linguistics with a different meaning). In organic states, it’s often the case that the phonemes are simple words or short sentences, often spoken by the second person as orders or abusive remarks. These abusive or imperative phonemes can also occur in schizophrenia, but other, more complicated speech is also heard.

The phonemes, or voices in the context of schizophrenia, can be single or multiple, male, female or both, people that the hallucinator recognises or unknown. Studies suggest there are often multiple voices, often male, speaking in the patient’s native tongue, but often with a different accent, sounding like it belongs to someone from a different social class from the patient.

Voices that say the patient’s own thoughts out loud (Gedankenlautwerde), voices providing a running commentary on their actions or voices that argue or discuss with each other, often referring to the patient in the third person, are particularly characteristic of schizophrenia. These are among Schneiderian first rank symptoms and are strongly suggestive of schizophrenia. In fact, first rank symptoms used to be considered pathognomonic of schizophrenia; however, it is now known that they can also be present in other conditions such as bipolar disorder.

Visual hallucinations

Visual hallucinations characteristically occur in organic states rather than in functional psychoses. Occipital lobe tumours, post-concussional states, epileptic twilight state, hepatic failure (any toxic delirium) and dementia are some of the conditions that can present with visual hallucinations.

Visual hallucinations are very uncommon in schizophrenia. However, visual pseudo-hallucinations described with auditory hallucinations are more commonly seen.

Complex, scenery-like hallucinations are described in oneiroid states of schizophrenia, which are altered states of consciousness that are characterised by a dream-like or hallucinatory quality. Oneiroid states can also be seen in bipolar disorder, severe depression or with the use of certain psychoactive substances.

Temporal lobe epilepsy

Simultaneous visual-verbal hallucinations are one of the common types of hallucinations experienced during temporal lobe seizures. These hallucinations can be accompanied by other symptoms, such as déjà vu or jamais vu, which involve feelings of familiarity or unfamiliarity with one’s surroundings or experiences.

Charles Bonnet Syndrome

A condition that causes complex visual hallucinations in individuals who have experienced significant vision loss or damage without any other demonstratable psychopathology or disruption of normal consciousness. This syndrome can occur at any age but is more common in the elderly. Often, there is full insight into the hallucinations, which can last for days or even years, and can be static or moving, and may be animated. It is an important condition to consider when making a diagnosis.

Delirium tremens

A specific form of acute organic syndrome associated with alcohol withdrawal is characterised by significant changes in perception, mood, and level of consciousness. In the prodromal stages of delirium, tremens, pareidolic or affective illusions may occur, which are followed by Lilliputian hallucinations in both the visual and haptic domains. These hallucinations often involve small animals or tiny people. Individuals with delirium tremens seeing Lilliputian hallucinations may experience a bizarre mix of emotions, including intense fear and childlike humorous responses to the absurdity of the experience, which is a common feature of this condition.

Tactile hallucinations

Tactile hallucinations, or ‘bodily sensation hallucinations’ as defined in Sims (2018), are a frequent occurrence in schizophrenia, and they are typically accompanied by delusional elaboration, frequently in the form of delusions of control.

Sims classifies hallucinations of bodily sensation into three main types:

• Superficial.
• Kinaesthetic.
• Visceral.

Superficial tactile hallucinations are the ones affecting skin sensation.

These can be:

• Thermic – Involves abnormal perception of heat and cold (such as feeling like one’s feet are on fire).
• Haptic – Involves touch (such as feeling like a dead hand has touched one).
• Hygric – Involves a perception of fluid (such as feeling like all the blood has dropped into one’s legs and there is a water level in the chest).

Tingling or ‘pins and needles’ sensations are referred to as paraesthesia, which can sometimes be delusionally ascribed but are often due to neurological issues, such as nerve compression.

Formication – A type of haptic hallucination that can be particularly unpleasant, and it involves a sensation of little animals or insects crawling over the body or just under the skin. This type of hallucination is commonly associated with drug states and withdrawal symptoms, such as cocaine addiction and alcohol withdrawal. It is frequently accompanied by delusions of infestation, although the latter can also occur without any hallucination.

Kinaesthetic hallucinations – Involves muscle or joint sense, where the patient may feel like their limbs are being bent or twisted, or their muscles are being squeezed. In schizophrenia, kinaesthetic hallucinations are often associated with bizarre somatic delusions.

Kinaesthetic hallucinations may also occur in organic states, alcohol intoxication and benzodiazepine withdrawal.

Visceral hallucinations – Sometimes also called coenesthetic hallucinations, are false perceptions of inner organs, and they usually involve a limited range of possible sensations such as pain, heaviness, stretching, distension, palpitation, or various combinations of these, like throbbing. People with schizophrenia can experience an endless variety of bizarre, false perceptions and interpretations.

Olfactory and gustatory hallucinations

Olfactory and gustatory hallucinations often occur in conjunction with each other, as the sense of smell significantly influences the perception of taste. These hallucinations can be challenging to differentiate from each other and from other sensory experiences.

Olfactory hallucinations, also known as phantosmia, can occur in many different conditions, including schizophrenia, organic states, epilepsy (particularly temporal lobe epilepsy) and, uncommonly, psychotic depression.

In depression, olfactory hallucinations can be associated with nihilistic delusions, such as the patient reporting they smell like a corpse because they are dead.

In epilepsy, olfactory hallucinations are common forms of an aura before a seizure and can be accompanied by visual, auditory, gustatory, and visceral hallucinations. Episodes of temporal lobe disturbance may be preceded by an unpleasant odour, such as burning paint or rubber. At times, these hallucinations may occur without any seizure, leading the patient to complain about a strange smell in their environment.

It can be challenging to determine whether an individual is experiencing an olfactory hallucination, an illusion, or a delusion. Some people may insist that they emit a smell, but it is crucial to ascertain if they can actually detect the odour. In many cases, individuals base their beliefs on the behaviour of others, such as nose wrinkling or comments about the smell. This is referred to as olfactory reference syndrome.

Gustatory hallucinations, disturbances of taste, can be caused by various factors, and it is often difficult to determine if these experiences are hallucinatory. In schizophrenia, gustatory hallucinations can accompany delusions about being poisoned.

Special types of perceptual abnormalities

Autoscopy

The experience of seeing oneself in external space and recognising that it is one’s own body. This phenomenon is also known as a phantom mirror image. Some authors speculate that reports of near-death out-of-body experiences in which individuals report seeing themselves rising to the ceiling and looking down at themselves in a hospital bed may be autoscopic hallucinations. While some authors consider autoscopy to be a visual hallucination, others argue it is not solely a visual hallucination because it also requires the presence of kinaesthetic and somatic sensations for the individual to perceive the hallucination as oneself. Then again, other authors argue that it’s a form of pseudo-hallucination, as it’s described by the patient as occurring in the internal space.

Autoscopy can occur in healthy individuals experiencing emotional distress or exhaustion. However, there is typically a change in consciousness. Epilepsy, focal lesions affecting the parieto-occipital region, and toxic infective states that affect the basal regions of the brain are the organic conditions most closely associated with autoscopy. While autoscopy is more commonly associated with acute and subacute delirious states, they may also be experienced by patients with schizophrenia and sometimes autoscopic hallucinations may stimulate the delusion that one has a double (doppelganger). Amongst all psychiatric diagnoses, however, the most common one associated with autoscopy is depression.

Negative autoscopy – Refers to the experience where a patient looks in the mirror and doesn’t see their reflection.

Extracampine hallucinations

Also known as ‘concrete awareness’, is a type of hallucination where the person perceives something outside of their sensory field. For example, they may feel that someone is behind them while looking straight ahead or hear voices from other cities. They are not of diagnostic importance as these hallucinations are not specific to any particular disorder and can occur in schizophrenia, epilepsy, and other organic states, as well as in healthy people during hypnagogic states. The person experiencing them perceives them as a real perception rather than just a belief or idea.

Hypnagogic and hypnopompic hallucinations

Perceptions experienced during the process of falling asleep (hypnagogic) and waking up (hypnopompic). While auditory hallucinations are the most common form of experience, they can also be visual, kinaesthetic or tactile and occur suddenly.

Hypnagogic hallucinations are about three times more common than hypnopompic hallucinations, with 37% of the adult population reporting them. These perceptions can also occur in conditions including narcolepsy, sleep paralysis, toxic states (fever, glue sniffing), post-infective depressive states, and phobic anxiety neuroses. Hypnopompic hallucinations are more specifically associated with narcolepsy compared to hypnagogic hallucinations.

The most common hypnagogic hallucinations are auditory ones. However, visual or tactile hallucinations can also be seen.

Although the subjects who experience hypnagogic hallucinations often assert they were fully awake, EEG records show that this is not the case, as a low alpha rhythm at the time of the hallucination.

It is important to recognise that hypnagogic and hypnopompic phenomena are not necessarily indicative of any psychopathology despite being true hallucinatory experiences.

Alcoholic hallucinosis

A rare condition that typically affects individuals with a chronic history of excessive alcohol consumption. The most common hallucinations experienced during alcoholic hallucinosis are unstructured sounds or voices, which may be threatening, abusive, or reproachful. These hallucinations often begin as simple noises but gradually progress to more complex voices, sometimes discussing the individual in the third person. These hallucinations usually occur during periods of relative abstinence and are typically accompanied by a clear sensorium, meaning that the individual is aware of their surroundings and not experiencing impaired consciousness. Alcoholic hallucinosis can be differentiated from other alcohol-related conditions, such as transient auditory hallucinations during withdrawal and delirium tremens, which involve disorganised hallucinations and impaired consciousness. Patients experiencing alcoholic hallucinosis are often distressed, anxious, and restless. The condition usually responds well to antipsychotic medication, and the prognosis is generally good. Symptoms often improve within days or a couple of weeks, provided that the individual remains abstinent.

Functional hallucinations

The term ‘functional hallucinations’ refers to a type of hallucination that only occurs in the presence of a real sensory stimulus, and both the sensory perception and the hallucination are experienced in the same modality. For example, a patient with schizophrenia may hear voices coming from a running tap or the chirping of birds.

The hallucination is distinct from the sensory stimulus, and the patient is able to distinguish between the two while simultaneously perceiving both of them. However, both are perceived as real. In some cases, patients may use strategies such as earplugs to reduce the intensity of the sensory stimulus and, hence, the hallucinations. These types of hallucinations are not uncommon in chronic schizophrenia and may be mistaken for illusions.

Reflex hallucinations

Reflex hallucinations are a rare type of hallucination that occurs as a result of stimulation of a sensory pathway that is not usually associated with that modality. They are often described as a morbid or hallucinatory form of synaesthesia, as a stimulus in one sensory field produces a hallucination in another. For example, someone who experiences a flash of light may also experience a sound or smell, even though the light itself would not usually be associated with those sensations.

These types of hallucinations are thought to be caused by cross-activation of adjacent sensory areas in the brain. They can occur in a variety of conditions, including migraine, epilepsy, and brain injury.

Reflex hallucinations are different from functional hallucinations, as functional hallucinations require the presence of a real sensory stimulus in the same modality.

Synaesthesia

Although not a hallucination, synaesthesia will be discussed here as it’s relevant to understand reflex hallucinations.
Synaesthesia is a perceptual phenomenon in which stimulation of one sensory or cognitive pathway leads to involuntary experiences in a second sensory or cognitive pathway. The experience can be described as a blending or mixing of sensory experiences, such as seeing colours when hearing sounds or tasting shapes. Synaesthesia can be congenital or acquired and is believed to involve aberrant neural connections between sensory regions of the brain. It is significantly more common in females and runs in families.

In one common form of synaesthesia, known as grapheme–colour synaesthesia or colour–graphemic synaesthesia, letters or numbers are perceived as inherently coloured.

Although rare, synaesthesia can occur under the influence of hallucinogenic drugs such as LSD or mescaline when the subject might describe feeling, tasting and hearing flowers simultaneously.

Pseudo-hallucinations

In Psychiatry, there are two different approaches to distinguishing pseudo-hallucinations from true hallucinations.

• Based on insight (Hare, 1973)
• Based on whether the image lies in inner or outer perceptual space (Jaspers, 1962)

For example, let’s imagine a patient who reports hearing voices other people can’t hear.

Based on the first approach, the voices would be considered an example of pseudo-hallucinations if the patient reports he knows they are not real.

Based on the second approach, the voices would be considered an example of pseudo-hallucinations if the patient reports he hears them ‘inside his head’.

These are important criteria that are often quite useful, and often they don’t contradict each other, as a patient who reports the voices are ‘inside his head’ might also report they are not real. However, this is not always the case, and in real clinical practice as well as the literature, it can be difficult to classify abnormal perceptions that match one description but not the other. For example, patients might report the perception to be in the inner subjective space but still believe it to be real. Or the opposite might be true, for example, the visual hallucinations in Charles Bonnet Syndrome, where the perception has all the other characteristics of hallucinations (such as being perceived as corporeal and tangible, vivid and not discernible from real perception), but the patient might have insight into them not being real.

There is significant controversy around different authors’ approaches to this definition, and what can be considered a pseudo-hallucination by one author might be considered a hallucination by another.

For the purpose of learning and passing RCPsych exams, it’s helpful to know both of these criteria (insight and inner/outer perceptual space).

Some examples of pseudo-hallucinations that might be asked in the exam could be in the context of Ganser syndrome, which is a rare dissociative disorder that’s also called prison psychosis, and it can present with approximate answers to questions, dissociative symptoms and pseudo-hallucinations. Another example of pseudo-hallucinations is seen in bereavement, where the bereaved report seeing their loved one; however, they are aware that this can’t be true and they are actually dead.

The following table might be useful for learning by comparison.

References

• Aggernaes, A. (1972). The experienced reality of hallucinations and other psychological phenomena. An empirical analysis. Acta Psychiatrica Scandinavica, 48(3), 220–238.
• Casey, P., & Kelly, B. (2019). Fish’s clinical psychopathology: Signs and symptoms in psychiatry. Cambridge, England: Cambridge University Press.
• Cutting, J., 1997. Principles of Psychopathology: Two Worlds – Two Minds – Two Hemispheres. Oxford University Press, Oxford.
• Esquirol, J.E.D., 1817. Hallucinations (Reprinted in Des Maladies Mentales, 1938). Baillière, Paris.
• Gelder, M., Andreasen, N. C., Lopez-Ibor, J. J., & Geddes, J. (Eds.). (2009). New Oxford textbook of psychiatry (2nd ed.). London, England: Oxford University Press.
• Hare, E. H. (1973). A short note on pseudo-hallucinations. The British Journal of Psychiatry: The Journal of Mental Science, 122(569), 469–476. doi:10.1192/bjp.122.4.469
• Jaspers, K. (1997). General psychopathology: Volume 1 (J. Hoenig & M. W. Hamilton, Trans.). Baltimore, MD: Johns Hopkins University Press.
• Ohayon, M. M., Priest, R. G., Caulet, M., & Guilleminault, C. (1996). Hypnagogic and hypnopompic hallucinations: Pathological phenomena? The British Journal of Psychiatry: The Journal of Mental Science, 169(4), 459–467. doi:10.1192/bjp.169.4.459
• Oyebode, F. (2018). Sims’ symptoms in the mind: Textbook of descriptive psychopathology(6th ed.). London, England: Elsevier Health Sciences.
• Sadock, B. J., Ruiz, P., & Sadock, V. A. (2017). Kaplan and Sadock’s Comprehensive Textbook of psychiatry. Saint Paul, MN: LWW.