Perception

Perception

Dr.safeyya Adeeb Alchalabi

Perception

Is the method by which the brain takes all the sensations a person experiences at any given moment and allows them to be interpreted in some meaningful fashion.

Gestalt principles

Gestalt principles
Figure-ground relationships Refer to the tendency to perceive objects or figures as existing on a background. Organization depends what we see as figure (object) and what we perceive a ground (context).

Figure-ground relationships

Depth perception
The capability to see the world in three dimensions. It seems to develop very early in infancy, if it is not actually present at birth.

Depth perception

Perceptual illusion
A false perception of actual stimuli involving a misperception of size, shape, or the relationship of on element to another.

Perceptual illusion

Muller-Lyer illusion

Moon illusion

Perceptual set (perceptual expectancy)

Disorders of perception

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


Sensory distortions Changes in intensity Changes in quality Changes in spatial form Distortions of the experience of time

Changes in quality It is mainly visual perceptions that are affected by this, brought about by toxic substances. xanthopsia (Colouring of yellow), chloropsia (Colouring of green), erythropsia (Colouring of red). These are mainly the result of drugs(for example, santonin, poisoning with mescaline or digitalis) used in the past to treat various disorders.

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. macropsia or megalopsia. can result from retinal disease (oedema , or scarring of the retina). disorders of accommodation and convergence posterior temporal and parietal lobe lesions (most commonly may occur either during the aura or in the course of the fit itself). Schizophrenia (rarely). poisoning with atropine or hyoscine (occasionally) high-altitude pilots (rare). chronic arachnoiditis

Distortions of the experience of time severe depression (psychotic depressive symptoms), the patient may feel that time passes very slowly and even stands still. mania manic patient feels that time speeds by and that the days are not long enough to do everything. schizophrenia Some patients with schizophrenia believe that time moves in fits and starts, and may have a delusional elaboration that clocks are being interfered with. 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. temporal lobe lesions patient with temporal lobe lesions may complain that time either passes slowly or quickly.

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.

Illusions In illusions, stimuli from a perceived object are combined with a mental image to produce a false perception. Illusions in themselves are not indicative of psychopathology since they can occur in the absence of psychiatric disorder, for example the person walking along a dark road may misinterpret innocuous shadows as threatening attackers. Illusions can occur in delirium when the perceptual threshold is raised and an anxious and bewildered illusions can occur in any modality, for example, visual illusion (most common) ,auditory illusions

Hallucinations

Perceptions are

Mental images

Pseudo-hallucinations


Pseudo-hallucinations

Pseudo-hallucinations

Causes of hallucinations

Hallucinations of individual senses

Auditory hallucination

Auditory hallucination

Auditory hallucination

Auditory hallucination

Auditory hallucination

Auditory hallucination

Vision(visual hallucination)

Vision(visual hallucination)

Vision(visual hallucination)

Vision(visual hallucination)

Vision(visual hallucination)

Smell (olfactory hallucination)

Taste (gustatory hallucination)

Taste (gustatory hallucination)

tactile hallucinations classified into three main types:Superficial (most often have an organic origin) thermic, haptic, hygric, Paraestethic kinaestethic (affect the muscles and joints and the patient feels that their limbs are being twisted, pulled or moved. They occur in schizophrenia organic states (Vestibular sensations), delirium tremens. alcohol intoxication benzodiazepine withdrawal after a week’s sailing an undulating feeling may persist for a few days. Touch (tactile hallucination)


Touch (tactile hallucination)

Hallucinatory syndromes

Hallucinatory syndromes( 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. Functional hallucinations are not uncommon in chronic schizophrenia.

Special kinds of hallucination

Reflex hallucinations stimulus in one sensory field produces a hallucination in another. can occur under the influence of hallucinogenic drugs such as LSD or mescaline when

Special kinds of hallucination

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

Special kinds of hallucination

Autoscopy or phantom mirror-imagethe experience of seeing oneself and knowing that it is oneself. This symptom can occur in healthy subjects when they are emotionally upset or when exhausted. hysterical symptom.schizophrenia acute and sub-acute delirious states (more common). Epilepsy (focal lesions affecting the parieto−occipital region and toxic infective states whose effect is greatest in the basal regions of the brain). negative autoscopyA few patients suffering from organic states look in the mirror and see no image. Internal autoscopy the subject sees their own internal organs..

Special kinds of hallucination

Hypnagogic and hypnopompic hallucinations These hallucinations occur when the subject is falling asleep or waking up respectively. Healthy people Narcolepsy.

Organic hallucinations

Organic hallucinations can occur in any sensory modality Organic visual hallucinations temporal lobe lesions. Charles Bonnet syndrome consists of visual hallucinations due to impaired vision . dementias delirium substance abuse are associated .

organic somatic hallucination phantom limb (amputated, loss of sensation). phantom organs (mastectomy, enuleation of the eye, removal of the larynx or the construction of a colostomy). distortion or splitting-off of body parts (Lesions of the parietal lobe).

The patient’s attitude to hallucinations

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