A.      Disorders of Sensation and Perception
1.      Sensory Disorders – disorders that affect the sentient cognitive processes
     a)   Anaesthesia/ Anesthesia – loss of sensitivity that may either be due to a psychological or psychogenic cause.
Ex. Glove/ stocking anaesthesia – only specific parts of the body have anaesthesia, in this case in the hands and in the legs respectively.
     b)   Hyperesthesia – increased or higher than normal sensitivity
     c)   Hypoesthesia – decreased sensitivity
     d)   Paraesthesia – false/ perverted sensitivity

2.      Perception Disorders – perception is sensation + meaning; any perceptual disturbance will cause an abnormality in the interpretation of sensed sensory stimuli.
     a)   Illusion – perceptual disturbance in the presence of stimulus; a distortion of perception and an erroneous interpretation of present stimulus
  • Normal Illusion – this type of illusion is normal when everyone can sense the stimulus.
Ex. Optical illusions are illusions that involve vision (Reber et al., 2009).
NOTE: Epicritic/ Discriminative sensibility – ability of locating stimuli that are applied on the body; this ability is normal to everyone.

  • Abnormal Illusion – an illusion is abnormal when not everybody can experience the illusion
·         Allochiria – wrong perception of stimuli or there is a displaced sensation.
·         Dyschiria – difficulty in localizing stimulus applied in the body.

     b)   Hallucination – the perceptual distortion in the absence of the stimulus.
     c)   Agnosia – the patient appears to be confused that he cannot see meaning or cannot identify and recognize the stimuli acting on the senses. 

Reber, A. S., Allen, R., & Reber, E. S. (2009). Penguin dictionary of psychology. (4th ed.). London, England: Penguin Books   Ltd.

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