Disorders of Perception

 Disorders of Perception

Disorders of perception can be divided into sensory distortions and sensory deceptions.

• In distortions ​there is a constant real perceptual object, which is perceived in a distorted way,

• sensory deceptions ​a new perception occurs that may or may not be in response to an external stimulus.

Sensory distortions ​These are changes in perception that are the result of a change in the intensity and quality of the stimulus or the spatial form of the perception.

Changes in intensity (hyper- or hypo-aesthesia)

Increased intensity of sensations (hyperaesthesia)-may be the result of intense emotions or a lowering of the physiological threshold.Anxiety and depressive disorders as well as hangover from alcohol and migraine are all associated with increased sensitivity to noise (hyperacusis) so that even day-to-day noises such as washing crockery are magnified to the point of discomfort.

• Hypoacusis occurs in delirium, where the threshold for all sensations is raised.

• The defect of attention found in delirium further reduces sensory acuity.This highlights the importance of speaking to the delirious patient more slowly and louder than usual.

• Hypoacusis is also a feature of other disorders associated with attentional deficits such as depression and attention-deficit disorder.

Changes in quality-​It is mainly visual perceptions that are affected by this, brought about by toxic substances.yellow,- xanthopsia, green- chloropsia Red-erythropsia

• In derealisation everything appears ​unreal​ and strange, while in mania objects look perfect and beautiful.

Changes in spatial form (dysmegalopsia)-This refers to a change in the perceived shape of an object.

• Micropsia​ is a visual disorder in which the patient sees objects as smaller than they really are.

• The opposite kind of visual experience is known as macropsia or megalopsia.

• This definition of micropsia includes the experience of the retreat of objects into the distance without any change in size although some authors call this porropsia.

• The terms macropsia and micropsia have also been used to describe the changes of size in dreams and hallucinations (​Lilliputian hallucinations​).

• Some authors reserve the term​ dysmegalopsia to describe objects that are perceived to be larger (or smaller) on one side ​than the other .

• Others use the term ​metamorphosia​ rather than dysmegalopsia to describe objects that are ​irregular in shape.

• Dysmegalopsia can result from retinal disease, disorders of accommodation and convergence but most commonly from temporal and parietal lobe lesions.

• In oedema of the retina ​visual elements are separated ​so that the image falls on what is functionally a smaller part of the retina than usual. This gives rise to ​micropsia.Scarring​ of the retina with ​retraction​ naturally produces macropsia, the ​distortion produced by scarring​ is usually irregular, metamorphopsia is more likely to result.

• Complete paralysis of accommodation​ or overactivity of accommodation during near vision is likely to cause ​macropsia,

• while ​partial paralysis of accommodation​ will lead to the experience during near vision that the object is very near, i.e. ​micropsia ​will occur.

• If accommodation is normal but ​convergence is weakened, macropsia​ occurs and vice versa.

Distortions of the experience of time

• From the psychopathological point of view there are two varieties of time:​ physical and personal,

• Slowing down of time is most marked in those with psychotic depressive symptoms.

• By contrast the manic patient feels that time speeds by and that the days are not long enough to do everything.

• In acute organic states, disorders of personal time are shown in temporal disorientation and in milder forms there may be an overestimation of the progress of time.

Sensory deceptions

• These can be divided into illusions​, which are misinterpretations of stimuli arising from an external object, and hallucinations, ​which are perceptions without an adequate external stimulus.

• In illusions, stimuli from a perceived object are combined with a mental image to produce a false perception.

• Illusions can occur in delirium​ when the perceptual threshold is raised and an anxious and bewildered patient misinterprets stimuli.

Three types of illusion are described (Sims, 2003) as follows:

• Completion illusions:​ these depend on inattention such as misreading words in newspapers or missing misprints because we read the word as if it were complete.

• Affect illusions:​ these arise in the context of a particular mood state.

• Pareidolia​: this is an interesting type of illusion, in which vivid illusions occur without the patient making any effort. These illusions are the result of excessive fantasy thinking and a vivid visual imagery. They cannot therefore be explained as the result of affect or mind-set, so that they differ from the ordinary illusion.

• These illusions are the result of excessive fantasy thinking and a vivid visual imagery. They cannot therefore be explained as the result of affect or mind-set, so that they differ from the ordinary illusion.

Hallucinatory syndromes
Hallucinatory syndromes, also termed hallucinosis, refer to those disorders in which there are persistent hallucinations in any sensory modality in the absence of other psychotic features. The main hallucinatory syndromes that are identified are:

• alcoholic hallucinosis;​ these hallucinations are usually auditory and occur during periods of relative abstinence. They may be threatening or reproachful, although some patients report benign voices. Sensorium is clear and hallucinations rarely persist longer than 1 week and are associated with long-standing alcohol misuse

• organic hallucinosis​; these are present in 20−30% of patients with dementia, especially of the Alzheimer type, and are most commonly auditory or visual. There is also disorientation and memory is impaired.

Special kinds of hallucination

• Functional hallucinations​ -An auditory stimulus causes a hallucination but the stimulus is experienced as well as the hallucination. In other words the hallucination requires the presence of another real sensation.

Reflex hallucinations

• Synaesthesia​ is the experience of a stimulus in one sense modality producing a sensory experience in another.

• Reflex hallucinations are a morbid form of synaesthesia. In a reflex hallucination a stimulus in one sensory field produces a hallucination in another.

• Extracampine hallucinations​ The patient has a hallucination that is outside the limits of the sensory field.These hallucinations can occur in healthy people as hypnagogic hallucinations but also in schizophrenia or organic conditions, including epilepsy.

• Autoscopy or phantom mirror-image -Autoscopy, also called phantom mirror-image​, is the experience of seeing oneself and knowing that it is oneself. It is not just a visual hallucination because kinaestethic and somatic sensation must also be present to give the subject the impression that the hallucination is oneself

• This symptom can occur in healthy subjects when they are emotionally upset or when exhausted. In these cases there is some change in the state of consciousness. Occasionally autoscopy is a hysterical symptom.

• A few patients suffering from organic states look in the mirror and see no image, known as ​negative autoscopy

• Hypnagogic and hypnopompic hallucinations First mentioned by Aristotle, these hallucinations occur when the subject is falling asleep or waking up respectively.It has been suggested that hypnopompic hallucinations are often hypnagogic experiences thatoccur in the morning when the subject is waking and dosing-off again, so that they actually happen when the subject is falling asleep.

• Hypnagogic hallucinations​ occur during drowsiness, are discontinuous, appear to force themselves on the subject and do not form part of an experience in which the subject participates as they do in a dream.

• Hypnagogic visual hallucinations may be geometrical designs, abstract shapes, faces, figures or scenes from nature.

• The importance of hypnagogic and hypnopompic phenomena is to recognise that they are not indicative of any psychopathology even though they are true hallucinatory experiences . They also occur in narcolepsy.

Organic hallucinations

• Organic hallucinations can occur in any sensory modality and they may occur in a variety of neurological and psychiatric disorders.

• Organic visual hallucinations occur in eye disorders as well as in disorders of the central nervous system and lesions of the optic tract.

• Complex scenic hallucinations occur in temporal lobe lesions. Charles Bonnet syndrome consists of visual hallucinations in the absence of any other psychopathology, although impaired vision is present.

• All the dementias as well as delirium and substance abuse are associated with visual hallucinations.

• The phantom limb ​is the most common organic somatic hallucination of psychiatric origin.

• In this case the patient feels that they have a limb from which in fact they are not receiving any sensations either because it has been amputated or because the sensory pathways from it have been destroyed.

• In rare cases with thalamo−parietal lesions the patient describes a third limb.

• In most phantom limbs the phenomenon is produced by peripheral and central disorders.

• Lesions of the temporal lobe are associated with multi-sensory hallucinations but they do not include somatic hallucinations, which is to be expected because the somatic sensory area is separated from the temporal lobe by the Sylvian fissure.