Psychopathology: disturbances of perception, attention, and memory – characteristics and clinical conditions
How perception, attention and memory fail. Sensory distortions, illusions and hallucinations by modality, pseudohallucinations, depersonalisation and derealisation; distractibility, poor concentration, hypervigilance and neglect; the kinds of amnesia, confabulation and the other paramnesias, and Korsakoff syndrome, with the conditions in which each is seen.
- 13 min read
- 5 questions
- Checked 26 Oct 2026
Contents3 sections
At a glance
- Perception can be distorted (a real stimulus changed in intensity, quality or size), misread (an illusion), or arise without any stimulus (a hallucination). True hallucinations feel like real perceptions in outer space; pseudohallucinations are a debated category that does not rule out psychosis.
- The modality points to the cause: auditory hallucinations to the functional psychoses, visual ones to organic states (delirium, dementia with Lewy bodies, drugs, eye disease), olfactory and gustatory ones to temporal lobe epilepsy as well as psychosis.
- Command hallucinations, especially to harm oneself or others, are a risk to be asked about directly.
- Depersonalisation and derealisation are "as if" feelings of unreality of the self or the world, with insight kept, common in anxiety, depression, fatigue and epilepsy.
- Inattention is the cardinal feature of delirium; distractibility marks mania and ADHD; hypervigilance PTSD and paranoia; unilateral neglect a right parietal lesion.
- Memory is registered, retained and recalled. Organic amnesia mainly impairs new learning (anterograde), with an older, temporally graded retrograde loss; dissociative amnesia loses autobiographical memory and sometimes identity, with new learning intact.
- Korsakoff syndrome, from thiamine deficiency, is dense anterograde amnesia with confabulation. Suspected Wernicke encephalopathy is treated at once with parenteral thiamine.
Disturbances of perception
Perception turns sensations into meaningful experience by joining them with memory and expectation. Its disturbances fall into three groups: a real stimulus perceived in a changed way (sensory distortion), a real stimulus perceived as something else (illusion), and a perception with no stimulus at all (hallucination); a fourth, depersonalisation and derealisation, changes the experience of the self and the world.
Sensory distortions
| Distortion | Characteristics | Clinical conditions |
|---|---|---|
| Heightened intensity (hyperaesthesia, hyperacusis) | sounds too loud, lights too bright, touch unpleasant | migraine, anxiety, hangover and withdrawal states, early psychosis, hallucinogens |
| Reduced intensity | colours dull, food tasteless, the world grey | depression, dissociation, delirium |
| Changed quality | colours altered (yellow vision from digoxin), things look sinister or strange | drug toxicity, hallucinogens, early schizophrenia |
| Changed size and shape (dysmegalopsia) | objects smaller and further away (micropsia), larger (macropsia) or distorted (metamorphopsia); the "Alice in Wonderland" syndrome | retinal disease, temporal and parietal lobe epilepsy, migraine, Epstein–Barr virus infection in children |
| Changed sense of time | time passing slowly or rushing | depression, mania, hallucinogens, epilepsy |
| Synaesthesia | a stimulus in one sense felt in another, such as "seeing" sounds | hallucinogens, epilepsy; also lifelong in some healthy people |
Illusions
An illusion is a misperception of a real stimulus, which merges with mental imagery into something it is not. It is common in health and usually disappears with closer attention.
| Type | Characteristics | Seen in |
|---|---|---|
| Affect illusion | the misperception follows a strong emotion: a coat on a door seen as an intruder by a frightened person | fear, anxiety, delirium |
| Completion illusion | the brain fills in what is missing: a misprint read as the right word | normal, inattention, fatigue |
| Pareidolia | vivid images made out of vague patterns, faces in clouds or a fire, which persist with attention | normal; strikingly in delirium and dementia with Lewy bodies |
Illusions increase when the level of stimulation is low and consciousness is clouded, which is why they are so typical of delirium, at night, in a dim room.
Hallucinations
A hallucination is "a perception without an object" (Esquirol). A true hallucination has the qualities of a real perception: it is vivid, it seems to come from outer, objective space, and it is not willed and cannot be dismissed. It lacks only the confirmation of other people. Hallucinations are described by their modality, their form (elementary, such as flashes and noises, or complex, such as voices and scenes), their content and the patient's response.
| Modality | Characteristics | Clinical conditions |
|---|---|---|
| Auditory | elementary noises; voices speaking to the patient in the second person ("you are worthless"), or about him in the third person (commenting, arguing); thought echo; music | schizophrenia (third-person voices, running commentary, thought echo are first-rank symptoms), psychotic depression (derogatory, mood-congruent second-person voices), mania, alcoholic hallucinosis (voices in clear consciousness, F10.52), organic psychoses; musical hallucinations in older people with hearing loss |
| Visual | elementary (flashes, colours) or complex (people, animals, scenes); Lilliputian (tiny people or animals) | delirium and delirium tremens, dementia with Lewy bodies, Parkinson's disease and its drugs, hallucinogens and stimulants, occipital lesions and epilepsy, migraine aura, Charles Bonnet syndrome in visual loss; less common in schizophrenia |
| Olfactory | usually unpleasant smells: burning, rotting, gas | temporal lobe (uncinate) seizures, schizophrenia, psychotic depression, brain tumours |
| Gustatory | strange or foul tastes, often linked to a belief in poisoning | temporal lobe epilepsy, schizophrenia |
| Tactile (haptic) | being touched, crawled on (formication), sexually interfered with | cocaine and amphetamine use, alcohol withdrawal, delusional infestation, schizophrenia |
| Somatic and visceral (coenaesthetic) | sensations inside the body: organs moving, rotting, electricity | schizophrenia, psychotic depression with nihilistic delusions |
| Kinaesthetic | false sense of limbs moving or the body floating | alcohol and benzodiazepine withdrawal, schizophrenia |
Special kinds of hallucination:
| Kind | Characteristics | Seen in |
|---|---|---|
| Functional | a real stimulus brings on a hallucination in the same sense, both perceived together: voices heard only while the tap runs | schizophrenia |
| Reflex | a stimulus in one sense brings on a hallucination in another: a touch brings a voice | schizophrenia, hallucinogens |
| Extracampine | outside the possible range of the senses: voices from another city, a figure seen behind one's back | schizophrenia, epilepsy, organic states |
| Autoscopic | seeing one's own double | epilepsy, migraine, schizophrenia |
| Hypnagogic and hypnopompic | brief hallucinations while falling asleep or waking, often with a sense of a presence | normal; frequent in narcolepsy, with sleep paralysis and cataplexy |
| Command | voices instructing the patient to do something, sometimes to harm himself or others | schizophrenia, psychotic depression, PTSD and personality disorders |
| Bereavement | seeing or hearing a dead partner | normal grief |
Pseudohallucinations are a disputed category. In one sense (Kandinsky, Jaspers) they are vivid perceptions experienced in inner, subjective space, "in my head", rather than outside; in another they are perceptions recognised as unreal. They occur in grief, PTSD, dissociative and personality disorders, and with hallucinogens, but many people with schizophrenia hear their voices inside the head, so locating a voice inside does not exclude psychosis.
Depersonalisation and derealisation
Depersonalisation is a feeling that one's self has become unreal, distant or detached, as if one were an observer of one's own body and actions, a robot, or emotionally numb. Derealisation is the same feeling about the surroundings: the world looks flat, foggy, dreamlike, as if seen through glass. Both have an "as if" quality, with insight kept: the patient says "I feel as if I were not real", not "I am dead", which would be a nihilistic delusion. They are unpleasant and frightening, and patients fear they are going mad.
They are common and non-specific: brief episodes occur in many healthy people with fatigue, sleep loss or stress, and they come with panic attacks, anxiety and depressive disorders, PTSD and other dissociative states, emotionally unstable personality disorder, temporal lobe epilepsy, migraine, cannabis, ketamine and hallucinogens, and early schizophrenia. When persistent and primary they are the depersonalisation-derealisation syndrome (F48.1 in ICD-10, a dissociative disorder in ICD-11 and DSM-5-TR; see dissociative disorders).
Disturbances of attention
Attention is the capacity to select what is processed: to direct, focus and sustain it (concentration), to divide it, and to shift it. It depends on arousal from the brainstem and on frontal and parietal networks, and every other cognitive function depends on it. Some European traditions describe it by its tenacity, the ability to hold it, and its vigility, the ability to move it, with hypoprosexia for weakened and hyperprosexia for overfocused attention.
| Disturbance | Characteristics | Clinical conditions |
|---|---|---|
| Inattention | reduced ability to direct, focus, sustain and shift attention: loses the thread, cannot hold a question in mind | delirium (its cardinal feature, often fluctuating), dementia with Lewy bodies, intoxication, severe fatigue |
| Distractibility | attention pulled by every irrelevant stimulus, a passing noise, an object in the room | mania, ADHD, delirium, anxiety |
| Poor concentration | cannot sustain attention: unable to read, follow a film or work | depression, anxiety, ADHD, insomnia, chronic pain, substances, dementia |
| Hypervigilance | constant scanning for threat, with an exaggerated startle | PTSD, paranoid states, stimulant intoxication, anxiety |
| Narrowed or captured attention | attention held by one theme or by inner experience: health fears, threat, rumination, voices | hypochondriasis, anxiety, depression, psychosis (attending to voices), dissociation |
| Inattention of ADHD | from childhood, in every setting, with careless errors, losing things and forgetfulness | hyperkinetic disorder and adult ADHD |
| Unilateral neglect | failure to attend and respond to one side of space or of the body, usually the left, without blindness or weakness to explain it | right parietal (and frontal) lesions, mostly stroke |
Attention is tested by the months of the year or days of the week backwards, digit span (about five to seven forwards is normal), serial sevens and spelling WORLD backwards (both depend on education). In neglect the patient eats from one half of the plate, shaves half the face, bisects a line off-centre, crowds all the numbers onto one side of a clock, and often denies any problem (anosognosia).
Disturbances of memory
How memory works
Memory has three stages: registration (encoding), retention (storage and consolidation) and recall (retrieval), and recognition is easier than free recall. Its systems differ in what they hold and where:
| System | What it holds | Where | Tested by |
|---|---|---|---|
| Working memory | a few items held and handled for seconds | prefrontal and parietal cortex | digit span, months backwards |
| Episodic memory | personal events in their time and place | hippocampus and medial temporal lobe, with the mammillary bodies, fornix and thalamus (the Papez circuit) | recall of a name and address after 5 minutes, recent events |
| Semantic memory | facts, word meanings, concepts | anterior and lateral temporal cortex | naming, general knowledge, verbal fluency |
| Procedural memory | skills and habits | basal ganglia, cerebellum | watching the patient dress or use a tool |
The word "short-term memory" is used loosely in the clinic for recall over minutes; it is clearer to speak of working memory, and of anterograde and retrograde memory.
Amnesia
Amnesia is a loss of memory. Anterograde amnesia is an inability to learn new information from the onset of an illness or injury onwards; retrograde amnesia is the loss of memories from before it, and is usually temporally graded, recent memories lost more than remote ones (Ribot's law). Amnesia for the period of an altered state itself, such as delirium, a twilight state or unconsciousness, may be total or patchy, with islands of memory.
| Condition | Pattern | Notes |
|---|---|---|
| Korsakoff syndrome | dense anterograde amnesia, retrograde loss over years with a gradient, confabulation; working memory and intellect relatively kept | thiamine deficiency, usually with alcohol (F10.6), also after hyperemesis, bariatric surgery or malnutrition (F04) |
| Alzheimer's disease | early anterograde episodic loss, rapid forgetting, recent before remote; later semantic and retrograde | see dementias |
| Herpes simplex encephalitis | severe anterograde and retrograde amnesia from medial temporal damage | treated with aciclovir as soon as suspected |
| Hypoxic brain injury | anterograde amnesia from hippocampal damage | cardiac arrest, carbon monoxide, near drowning |
| Head injury | post-traumatic amnesia (the period of confusion after the injury, whose length reflects its severity), a short retrograde loss | |
| Transient global amnesia | sudden anterograde amnesia with repetitive questions, patchy retrograde loss, identity kept, resolving within 24 hours | aged 50 to 70; after exertion, cold water, emotion; benign, and recurs in only about one in ten; brief or rapidly repeated attacks suggest transient epileptic amnesia |
| Transient epileptic amnesia | brief, recurrent episodes, often on waking | temporal lobe epilepsy in older adults; responds to antiepileptics |
| Drugs and alcohol | anterograde amnesia for the period of use; alcoholic blackouts (palimpsests) | benzodiazepines and Z-drugs, alcohol, anticholinergics |
| ECT | anterograde amnesia during the course, patchy retrograde loss around it | see ECT |
| Depression | complaints of poor memory outweigh the deficit; "don't know" answers, poor effort; improves with treatment | "depressive pseudodementia", which can also precede dementia |
| Dissociative amnesia and fugue | loss of autobiographical memory, often for a stressful period; in a fugue, travel and sometimes a new identity | F44.0 and F44.1 |
Organic and dissociative amnesia are told apart by their pattern:
| Organic amnesia | Dissociative amnesia | |
|---|---|---|
| Onset | with an illness, injury or drug | after severe stress or trauma |
| Main loss | new learning (anterograde) | autobiographical memory (retrograde), a period or a theme |
| Personal identity | kept until very late | may be lost |
| New learning | impaired | intact |
| Skills and general knowledge | kept in most | kept |
| Course | follows the cause | often recovers suddenly |
Point at a name or a part to light it.
Anterograde amnesia is the inability to lay down new memories from the onset of an illness or injury; retrograde amnesia is the loss of memories from before it, usually graded, the recent lost more than the remote (Ribot's law). In Korsakoff syndrome the anterograde loss is dense and the retrograde loss reaches back years, and the gaps may be filled by confabulation; in Alzheimer's disease the anterograde loss comes first; after a head injury the retrograde loss is usually short.
Simplified: time is not to scale, and real gradients and spans vary with the cause; the onset is drawn as a moment; in Alzheimer's disease it creeps in over years; memories drawn as separate beads; memory is not stored as separate items; one dense pattern is drawn; many amnesias are partial, with islands of memory kept.
2 sources
- Semple D, Smyth R. Oxford Handbook of Psychiatry, 4th edition. Oxford University Press, 2019. Chapter 2, Abnormal cognitive function; chapter 3, Symptoms of psychiatric illness (memory).
- Kopelman MD. Disorders of memory. Brain, 2002;125(10):2152–2190.
Paramnesias
The paramnesias are distortions of memory rather than losses.
| Disturbance | Characteristics | Clinical conditions |
|---|---|---|
| Confabulation | false memories produced without intent to deceive, filling gaps: provoked (plausible answers to questions) or spontaneous (often fantastic) | Korsakoff syndrome, frontal lesions (anterior communicating artery aneurysm), dementia; differs from pseudologia fantastica, the elaborate lying of factitious disorder |
| Déjà vu | a new experience feels as if lived before | common in health; frequent, stereotyped episodes with other aura features in temporal lobe epilepsy; anxiety, fatigue |
| Jamais vu | a familiar situation feels unknown | temporal lobe epilepsy, fatigue, depersonalisation, schizophrenia |
| Retrospective falsification | the past is unconsciously reshaped to fit the present mood or belief | depression (a past seen as all failure), paranoid states, and everyone to some degree |
| False memories | sincere memories of events that did not happen, or did not happen so | normal memory is reconstructive; suggestion, leading questions and repeated imagining create them, including "recovered memories" in some therapies; important in court |
| Delusional memory | a memory given a new delusional meaning, or a false memory held with delusional conviction | schizophrenia (see thought disturbances) |
| Reduplicative paramnesia | a belief that a place has been duplicated or moved, such as a hospital that is "really" in the patient's home town | right hemisphere and frontal lesions, dementia |
| Hypermnesia | unusually vivid or detailed recall | mania, some intoxications; in PTSD the intrusive memories of the trauma, re-lived as if happening now (flashbacks) |
Korsakoff syndrome and Wernicke encephalopathy
Thiamine (vitamin B1) deficiency first causes Wernicke encephalopathy, an acute state of confusion, eye signs (nystagmus, ophthalmoplegia) and ataxia, with lesions in the mammillary bodies, medial thalamus and periaqueductal grey. All three signs are present in only a minority, so it is suspected in anyone at risk with any of them, or with unexplained confusion; in people who drink, two of dietary deficiency, eye signs, cerebellar signs and an altered mental state or memory impairment are enough (the Caine criteria). It is treated at once with high-dose parenteral thiamine, before or with any glucose, for several days (European and UK regimens differ in dose), with magnesium corrected. Untreated, it can kill or leave Korsakoff syndrome.
Korsakoff syndrome (ICD-10 F10.6 when due to alcohol, F04 otherwise) is the lasting amnesic state, which can also develop without a recognised Wernicke episode: a dense anterograde amnesia, a retrograde loss of years with a temporal gradient, confabulation (most marked early), disorientation, apathy and little insight, while working memory, procedural memory and general intelligence are relatively kept. With abstinence and good nutrition many improve over months to years, but only a minority recover fully, and many need long-term support (see alcohol use disorders).
Check yourselfAnswer, then say how sure you were: a lucky guess still counts as a weak point.
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