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Visual hallucinations and illusions are caused by destructive and irritative lesions in any portion


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Title: Visual hallucinations and illusions are caused by destructive and irritative lesions in any portion

Visual hallucinations and illusions are caused by
destructive and irritative lesions in any portion
of the visual system
Complex (formed) visual hallucinations
  • Formed visual hallucinations usually occur with
    lesions in the temporal or parieto-occipital
    association areas. The images may appear to be
    moving, multiple or abnormal in size (most often,
    the images are perceived as smaller than their
    real counterparts, a phenomenon known as
    lilliputian hallucinations). Hallucinations
    caused by seizure discharges are typically brief,
    lasting less than three minutes and often less
    than 30 seconds, and are often associated with
    illusions or hallucinations in other sensory

  • Autoscopy is the hallucination or psychic
    experience of seeing oneself. There are two
    principal forms of autoscopic phenomena. The
    first is a complex psychosensorial hallucinatory
    perception of ones own body image projected into
    external visual space, or seeing ones double.
    An out-of-body experience is the feeling of
    leaving ones body and viewing it from another
    vantage point, usually from above.

  • Autoscopic phenomena occur in healthy persons,
    especially with anxiety and fatigue, and in those
    patients experiencing near-death phenomena,
    systematic illnesses, migraine and ictal
    discharges from temporal or parietal lobes
    without lateralized preferences.

  • Peduncular hallucinosis is a rare disorder in
    which vivid, well-formed visual hallucinations,
    such as a brightly colored parrot.

  • Epileptic phenomena is characteristically
    paroxysmal in onset and brief in duration.
  • Sensory deprivation or prolonged darkness can
    cause simple and complex hallucinatory
  • Release hallucinations occur after lesions of the
    visual pathway impair normal inhibitory visual
    mechanisms and are typically continuous,
    non-stereotyped and influenced by such purposeful
    acts as changing the direction of gaze. Among
    patients with visual release hallucinations,
    simple forms are more than twice as common as
    complex hallucinations.

  • Photopsias sparks or flashes are the most
    common type of simple visual hallucinations.
  • In patients with calcarine cortex lesions, visual
    hallucinations usually occur in areas of visual
    loss and tend to be continuous and unformed.
    These hallucinations are often associated with an
    element of movement, such as in weaving patterns,
    zigzag lights and a shower of sparks or colored

  • Scintillating scotomas and zigzag lines are most
    often found in classic migraine.
  • Scotomas are usually negative phenomena resulting
    from loss of normal sensory input, although they
    may be associated with such positive symptoms as
    halos of color, opacity or heat waves
    surrounding the black hole. However scotomas are
    positive phenomena that persist even in the dark
    or when the eyes are closed.

Visual Hallucinations
Hallucinatory Experiences
  • In earlier reviews of the psychiatric literature,
    Al-Issa (1977, 1978) found evidence of cultural
    and historical differences in the kinds of
    hallucinations recorded by psychiatrists. Visual
    hallucinations were found to be much more
    commonly recorded in developing countries than in
    the developed world, an observation that was
    confirmed in the WHOs multinational study of new
    cases of psychosis (Sartorius et al., 1986).

  • There is some evidence that a decline in the
    prevalence of visual hallucinations in the West
    has been matched by an increase in the recorded
    prevalence of auditory hallucinations.
    Hallucinatory experiences recorded in the Middle
    Ages were almost entirely visual (Kroll
    Bachrach, 1982). Lenz (1964), by contrast,
    examined psychiatric records from Vienna and
    found that reports of visual hallucinations
    decreased over a 100-year period, whereas reports
    of auditory hallucinations increased.

  • External stimuli and mental activities provoked
    by such stimuli have been shown to affect
    hallucinatory experiences. Although early
    research indicated that hallucinations could be
    elicited in ordinary people by periods of sensory
    deprivation, careful experimentation revealed
    that only a minority of participants reported
    vivid visual and auditory hallucinations in
    deprivation experiments and that suggestions from
    experimenters appeared to have played a role in
    these reports (Zuckerman, 1969).

  • Slade (1974) asked 2 patients to monitor their
    hallucinations while shadowing verbal information
    of varying complexity and found that the rate of
    hallucinations decreased as the complexity of the
    stimulus material increased.

  • Margo, Hemsley, and Slade (1981) carried out a
    similar procedure with 7 frequently hallucinating
    patients with schizophrenia. The nine conditions
    used in this investigation included no
    stimulation, reading aloud, listening to boring
    and interesting passages of text, listening to
    popular music, listening to regular and irregular
    patterns of electronic blips, listening to speech
    in a foreign language, sensory restriction and,
    finally, listening to white noise. In general,
    it was observed that the duration, loudness, and
    clarity of auditory hallucinations increased
    during sensory restriction and white noise but
    decreased while the participants were listening
    to meaningful stimulation or especially when they
    were reading aloud.

  • The observation that reading aloud suppresses
    auditory hallucinations has also been made in
    clinical studies, leading some clinicians to
    advocate reading as a coping strategy for
    hallucinating patients. A card-sorting task
    produced a reduction in the participants
    hallucinations, but this effect did not seem to
    be a function of the rate of information
    processing. The effect of card sorting was much
    greater when the participants were required to
    name the color of the card aloud, confirming that
    the requirement to speak had a specific
    inhibitory effect on auditory hallucinations.

  • It has been known for many years that inner
    speech in adulthood, even when silent, is
    accompanied by subvocalization or electrical
    activation of the speech muscles (McGuigan,
    1978) indeed, this hypothesis was suggested by
    J.B. Watson (1924), the founder of the American
    behaviorist school of psychology. The first
    studies that demonstrated a link between inner
    speech and hallucinations involved
    electromyographic (EMG) measurements of
    subvocalization in hallucinating patients. Gould
    (1948) measured passive lip and chin EMG activity
    in a large group of psychiatric patients and
    found increased activity in 83 of hallucinating
    patients but only in 10 of nonhallucinating

  • Gould (1949) then demonstrated that it was
    possible, using a sensitive microphone to record
    subvocal speech from a patient who was
    hallucinating. This technique was later
    replicated by Green and Preston (1981), who
    showed that the content of the recorded speech
    matched the content of their patients auditory
    hallucinations. Subsequent studies by Gould
    (1950) and others (Gabbard, Lazar, Hornberger,
    Spiegel, 1997 Green Kinsbourne, 1990 Inouye
    Shimizu, 1970 McGuigan, 1966) established that
    the onset of electromyographically recorded
    subvocalization coincided with the onset of
    hallucinations and that increased electrical
    activity was not concurrently observable from
    control muscles in other parts of the body.

  • McGuire et al. (1993) showed that auditory
    hallucinations were associated with activation of
    Brocas area (a region of the left frontal cortex
    responsible for speech production) and also of
    the left medial temporal lobe. In a subsequent
    study using the more sensitive PET methodology,
    Silbersweig et al. (1995) observed activation of
    the left frontal cortex but also in deeper brain
    structures (various subcortical nuclei and
    paralimbic regions).

  • In Silbergweig et al.s study, a single drug-free
    patient who experienced simultaneous visual and
    auditory hallucinations (of a disembodied head
    that talked to him) was also investigated. It
    was observed that the patients hallucinations
    were associated with activations in both the
    visual association cortex and the auditory
    association cortex in the left hemisphere.

  • These physiological observations, together with
    the earlier EMG studies, provide strong evidence
    that inner speech occurs concurrently with
    auditory hallucinations and, therefore, that
    hallucinations reflect the individuals mistaken
    judgments about the source or location of their
    inner speech.

Entoptic Phenomenon
  • The term entoptic derives from Greek, meaning
    literally within vision. Entoptic phenomena,
    or entoptics, are sensations produced by the
    structure of the visual nervous system the
    eyeball, the optic nerve and the parts of the
    brain dedicated to processing visual input.

  • In an entoptic experience, one has visual
    sensations that do not correspond to an external
    visual stimulus (known as a distal stimulus).
    The most familiar entoptics are the stars seen
    when one receives a blow to the back of the head.
  • Entoptics are distinguished from VISUAL
    HALLUCINATIONs, in that the latter are not
    products of the visual system rather,
    hallucinations are mental images, misinterpreted
    as external objects.

  • Under the right lighting conditions, the eyeball
    can view features of its own structure. The lens
    of the eye contains fibers that radiate from its
    center. In defective lenses, these fibers can
    cause a starlike luster to appear around distant
    lights. Debris drifting in the vitreous body
    (the transparent liquid between the iris and the
    retina), can cast shadows on the retina the
    resultant sensations are called FLOATERS.
    Sometimes, blood circulating through capillaries
    adjacent to the retinal light receptors can also
    be seen, an occurrence known as SCHEERERS
    PHENOMENON. The eyes are constantly quivering,
    which can impart a sense of motion to these
    entoptic effects.

  • Mechanical pressure on the eyeball can cause
    retinal cells to fire, creating the sparkling
    displays called PHOSPHENES.

  • A common type of ENTOPTIC PHENOMENON. The
    eyeball is filled with a transparent liquid, the
    vitreous body, through which light passes on its
    way from the pupil to the retina. Blood cells
    can leak into this area cells from the macula,
    or outer wall of the eyeball, can also become

  • Such debris, drifting through the path of the
    light traversing the vitreous body, casts shadows
    on the retina. One may then see small circles
    floating across the field of vision sometimes,
    these forms appear in chains or tangles.
    Floaters tend to become more common as a person
    ages. They are most easily seen when the light
    entering the eye is relatively bright and steady,
    as when one looks into the sky on a cloudless
    day. Floaters have been interpreted as visions
    of spirits, manifestations of psychic energy or
    even as signs of impending madness. In fact,
    they are the result of normal wear and tear on
    the visual system.

Form Constants
  • Geometric images produced by the human visual
    nervous system itself, rather than by external
    stimuli, form constants comprise an important

  • Unlike other species of entoptics, such as
    form constants are thought to be produced by
    regions of the visual system beyond the eyeball.
    In ordinary vision, light from the external world
    shines onto sensitive receptor cells in the
    retina the retinal cells send information to the
    thalamus and visual cortex of the brain, via the
    optic nerve. The brain constructs our visual
    perception of the world from this information.

  • When the activity of cells in the optic nerve and
    visual cortex does not represent events and
    objects in the outer world, form constants are

  • Form constants can occur spontaneously they have
    also been deliberately sought. Many conditions
    and techniques can cause entoptic visions.
    Anthropologists and psychologists have documented
    the following triggers of form constants
    AUDITORY and PHOTIC DRIVING, fatigue, rhythmic
    movements, SENSORY DEPRIVATION, concentration,
    DRUGS, MIGRAINE headaches, hyperventilation and
    SCHIZOPHRENIA. They have also been produced by
    direct electrical stimulation of the visual
    cortex. Each of these factors disrupts the
    ordinary functioning of the visual system,
    causing cells to fire abnormally.

  • This neural firing is not random, however.
    Numerous researchers, starting with Kluver in
    1926, have observed that form constants are
    usually geometric shapes, which fall into a
    limited number of classes. Lewis-Williams and
    Dowson reported six major types of form
    constants, based on a review of the literature
  • These are (1) a basic grid and its development in
    a lattice and expanding hexagonal pattern, (2)
    sets of parallel lines, (3) dots and short
    flecks, (4) zigzag lines crossing the field of
    vision (reported by some subjects as angular, by
    others an undulating), (5) nested catenary
    curves… and (6) filigrees or thin meandering

  • People undergoing one of the experiences that
    tend to produce form constants often report a
    sequence of phenomena. First, the geometric
    images themselves appear, flashing or glowing as
    they dart across the visual field. Siegal
    described the experiences of psychonauts-experim
    ental subjects who had taken hallucinogenic drugs
    and then carefully reported their sensations. At
    the outset of the psychonautical voyage, a
    luminous, tunnel-like image appeared in the
    middle of the visual field.

  • Then
  • Initial black-and-white images began to take on
    colors. They started to pulsate, moving toward
    the center of the tunnel or away from the bright
    light. Some images rotated like pinwheels while
    others darted across the visual field. The
    accelerated movements brought many new geometric
    forms, including various tunnel and lattice
    arrangements. The lattices included gratings,
    fretworks, honeycombs, and chessboard designs.
    There were also multicolored kaleidoscopic forms
    bursting from the tunnel, like so many flowers
    from a magicians hat. These geometric forms
    frequently cloned themselves or combined into
    ever-changing structures.

  • As the entoptic visions continue, they begin to
    transform into more complex objects. Generally,
    these images represent things familiar to the
    person and are affected by expectations and
    emotional states. Thus, a Huichol Indian who had
    eaten peyote in order to induce a religious
    vision described a big spiral and I saw the fire
    god in the center and rushing out toward me,
    Siegel reported.

  • In the third stage of entoptic experience,
    subjects may find themselves in the middle of a
    vortex or tunnel. This image marks a transition
    from the sensation of form constants to frank
    HALLUCINATIONs. Against a background of entoptic
    forms, frequently manifesting as an immense
    lattice of squares like a giant checkerboard,
    complex images arise. This display can be so
    vivid and emotionally charged that it is felt to
    be a perception of the external world. The
    attention of experients is now fully absorbed
    they may believe themselves to be in another

Hypnagogic State
  • Each night, as our brains shift from ordinary
    wakefulness to sleep, we pass through the
    hypnagogic state. This condition is typified by
    an upsurge in spontaneous mental content and
    especially by an increase in vivid sensations
    that are not produced by external sources.

  • In most studies around three-quarters of the
    respondents indicated that they had, at least
    occasionally, experienced visual sensations while
    drifting off to sleep. One of the most common
    hypnagogic experiences is seeing FORM CONSTANTS,
    the visions of geometric shapes caused by cells
    firing in the visual system whenever the normal
    waking state is disrupted.

  • Vivid visual imagery is also common during the
    hypnagogic transition. Hypnagogic images
    typically do not occur in a narrative sequence,
    as in dreams rather, a series of disconnected
    pictures appear. Brief images of unknown faces
    are most often reported. Children are sometimes
    frightened by this experience. Other solitary
    images can also arise.

  • Auditory sensations are also typical in the
    hypnagogic state. Hearing ones name called is
    the most frequent such experience. Music, both
    well-known and unfamiliar, is another common
    hypnagogic sound.

  • Poetry, gibberish and crashing sounds in ones
    head have also been reported. Hypnagogic smells
    are not uncommon, ranging from fetid stenches to
    floral scents.

  • A person can slip into a hypnagogic state without
    being aware of it. The visions and sounds might
    then be confused with perceptions of the external
    world. Such hypnagogic hallucinations are most
    likely when one has been deprived of sleep for
    long periods. Occasionally, however, the
    intrusion of hypnagogic material into the waking
    state occurs for no known reason. Hufford
    suspected that the OLD HAG EXPERIENCE is probably
    a kind of hypnagogic attack.

Hypnopompic State
  • As one awakens from sleep, one passes through an
    intermediate condition known as the hypnopompic
    state. Auditory and visual mental images of
    great vividness can occur during this time. 21
    of surveyed college students reported occasional
    hypnopompic experiences.

  • Hypnopompic visions and sounds can be so intense
    that they can be mistaken for perceptions of
    external events. However, such HALLUCINATIONS
    are often accompanied by telltale features that
    reveal their imaginal nature the hallucinator
    usually feels paralyzed and frequently, the
    hallucinator quickly falls asleep again following
    the experience.

  • Hypnopompic experiences can also be quite unlike
    ordinary life. Many cases of bedside encounters
    with strange creatures and ghosts are probably
    hypnopompic hallucinations. Baker described the
    following example of a nocturnal ghostly meeting,
    which displays the telltale signs of a
    hypnopompic event

  • I went to bed and went to sleep and then sometime
    near morning something woke me up. I opened my
    eyes and found myself wide awake but unable to
    move. There, standing at the foot of my bed was
    my mother, wearing her favorite dress the one
    we buried her in. She stood there, looking at me
    and smiling and then she said Dont worry about
    me, Doris, Im at peace at last. I just want you
    and the children to be happy. What did you do
    then? Nothing, I just closed my eyes and went
    back to sleep.

Ideoretinal Light
  • Flashes of light or color that appear in the
    field of vision in the absence of sensory
    stimulation. Ideoretinal light is often observed
    in the HYPNAGOGIC STATE. This occurrence is
    likely a type of ENTOPTIC PHENOMENON.

Illusion Des Sosies
  • The French phrase illusion des sosies, or
    illusion of doubles, refers to a condition in
    which someone becomes convinced that a familiar
    person has been replaced by an identical replica.
    This delusion is also called Capgrass Syndrome.
    The illusion des sosies may be an extreme
    variant of JAMAIS VU the perception of a
    well-known object without a feeling of

  • In most cases, a close friend or family member of
    the person suffering the illusion is thought to
    have been replaced. The sufferer develops a
    belief system to explain why the replacement has
    happened and resists all efforts to demonstrate
    the error of this conviction. Such loss of
    contact with reality is categorized as a

  • Twentieth century victims of illusion des
    sosies tend to blame aliens or secret government
    experiments for the replacement of their loved
    ones. In premodern times it was widely believed
    that fairies loved to kidnap humans, especially
    infants, and substitute replicas called

Isakower Phenomenon
  • During the transition between wakefulness and
    sleep the HYPNAGOGIC STATE some people have
    reported an impression of a round or amorphous
    shape that seems to loom momentarily in front of
    their eyes and then recede.

  • Psychiatrist Otto Isakower regarded the
    experience as an infantile memory of the mothers
    breast more likely, it is a type of ENTOPTIC
    PHENOMENON. It has been suggested that the
    Isakower phenomenon could be responsible for some
    accounts of apparitions or UFO occupants
    appearing at ones bedside.

(No Transcript)
Jamais Vu
  • This French phrase, meaning literally never
    seen, refers to a disorder of recognition the
    perception of a familiar object, accompanied by
    the feeling that one has never before encountered
    it. Jamais vu is the opposite of the more common
    déjà vu, in which a novel experience seems
    intensely familiar.

Lilliputian Hallucination
  • Named after the tiny people in Gullivers
    Travels, a type of VISUAL HALLUCINATION in which
    a person views small human figures. It can occur
    in a wide range of toxic drug reactions,
    neurological disorders and mental illnesses.
    Lilliputian hallucinations are the probable
    source of many old tales of encounters with the
    fairy folk.

  • A kind of perceptual distortion in which nearby
    objects are seen as very large. Macropsia can
    occur as an effect of psychedelic drugs, as well
    as a variety of NEUROLOGICAL DISORDERS.

  • A form of perceptual distortion in which nearby
    objects are seen as very small, as if looking
    through the wrong end of binoculars. Micropsia
    has been reported as an effect of psychedelic
    drugs and as a symptom of a NEUROLOGICAL

  • A rare condition in which a person hears vivid
    echoes of voices, music or other noises for a
    time after the triggering sound has stopped.
    Sometimes, only a part of the original sound is
    repeated. The cause of this annoying experience
    is unknown it is likely related to some type of

  • The recurrent visual images of objects long after
    they have been removed from sight. Palinopsia is
    linked to several types of NEUROLOGICAL DISORDER,
    including tumors and epilepsy. This condition is
    distinct from EIDETIC IMAGERY.

  • In palinopsia the images are symptomatic of a
    disease and occur involuntarily most who have it
    are adults. Eidetic images are unrelated to
    illness, under voluntary control and most
    commonly reported by children.

Phantom Vision
  • About 15 of people who lose all or part of their
    vision from eye injury or eye diseases experience
    this phenomenon. In phantom vision the person
    sees very realistic objects, even though visual
    information about the world is not reaching the

  • Most commonly visualized are normal-sized people
    and buildings tiny people and animals are less
    popular. These images are not mere memories as
    phantom visions of things never before seen can

  • Generally, people with phantom vision do not
    confuse the phantom forms with true percepts in
    these cases, the visions are classed as
    PSEUDOHALLUCINATIONS. Individuals who confuse
    their phantoms with perceived objects are having
    HALLUCINATIONS and are diagnosed as suffering
    from Antons Syndrome.

  • A variety of ENTOPTIC PHENOMENON. When a person
    presses or rubs the eyes, the squeezing of the
    eyeballs can cause the light receptors in the
    retina to fire, and the person may then see
    bright flashes and swirls of light. These
    sensations are called phosphenes.

  • A sensory experience that is as vivid as an
    actual perception, but which the person having it
    knows to be unreal. Pseudohallucinations differ
    from HALLUCINATIONS only in that the hallucinator
    believes the experience to be real.

  • A pseudohallucination may be so intense that it
    provokes an emotional reaction, such as fear or
    delight but the observer is still unfooled, as
    one who responds to a film does not believe the
    actors to be actually present. Voices or visions
    of deceased persons, experienced by 50 to 65 of
    the bereaved, are the most common type of

Retrospective Hallucination
  • Mistaking the memory of a fantasy for the memory
    of an actual event. Piaget reported a personal
    example As an adult, he could clearly recall an
    assault and robbery he supposedly witnessed when
    he was a young child. Later in life, he learned
    that the event he so vividly remembered had never
    taken place.

  • As a child, however, he had been informed about
    the alleged incident and had probably visualized
    it while being told the story. Subsequently, he
    remembered his own fantasy, believing it to be an
    accurate memory.

Scheerers Phenomenon
  • A type of ENTOPTIC PHENOMENON, or sensation
    arising from the structure of the visual system.
    In order to reach the light-sensitive receptor
    cells at the back of the retina, light must first
    pass through several intervening layers of
    retinal cells. These cells are nourished by a
    network of capillary blood vessels.

  • When the light entering the eye is bright and
    steady, it is sometimes possible to see streaking
    points of light and shimmering webs in the field
    of vision, caused by the blood flow in front of
    the receptors. Alternately straining and
    relaxing the facial muscles can cause the specks
    of light to accelerate and slow. Scheerers
    phenomenon can also be enhanced by circulation
    disturbances within the eye.

  • Individuals unfamiliar with the biological origin
    of the light sensations have tended to regard
    them as perceptions of spiritual phenomena.
    Zusne and Jones suggested that the psychic
    vitality globules reported by the theosophical
    writers Besant and Leadbeater were actually
    intraocular blood cells. Neher (1990) observed a
    clairvoyant group which believed that the flecks
    of light they saw were psychically magnified air

  • A type of AUDITORY HALLUCINATION in which
    nonsense phrases are heard repeated over and
    over. Verbigeration if often immensely
    distracting and tormenting for the sufferer. The
    condition occurs most frequently in connection

  • Kraeplin (quoted by Noll 1992a) described a
    patient who heard the following phrase, endlessly
    repeated For we ourselves can always hope that
    we should let ourselves pray other thoughts. For
    we ourselves wish to know who would let the
    swines head be tormented to death with us