Visuo-Perceptual Impairments

Introduction

The assessment of visuo-perceptual impairment after acquired brain injury is a difficult task in clinical practice. There are different reasons for this, the first being that, unless the deficit is so evident that it becomes a handicap for everyday living, many people who are visuo-perceptually impaired are normally not even aware of their impairment. Second, the tests and tasks used to evaluate or assess visual and perceptual functioning may lack the necessary accuracy to be able to detect subtle variations. Third, organizing a precise and effective neuropsychological assessment of visuo-perceptual functions requires a thorough understanding and knowledge of the concept and theory regarding these functions. And fourth, people sustaining brain injury normally have cognitive, emotional, and behavioural disorders that normally interact with the visuo-perceptual deficit, especially attention, language, memory, and motor impairments. The correct neuropsychological assessment of these functions requires a trained neuropsychologist with expertise in this field.

The assessment of visuo-perceptual functioning must be preceded by a careful neuro-ophthalmological examination of the most elementary components of vision. This is due to the fact that visual defects may be confused with visual agnosic problems. In addition, it is necessary to delimit elementary and higher visual functions which are not always clearly differentiated.

The neurological exploration of visuo-perceptual functioning must include:

• (a)
  Examination of visual fields.
• (b)
  Assessment of visual perception of objects and pictures.
• (c)
  Assessment of visuo-spatial orientation.
• (d)
  Assessment of colour perception recognition.
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• (e)
  Assessment of visual scanning.
• (f)
  Assessment of neglect.

The Examination of Visual Fields

In neuropsychology, the examination of the visual fields is important in order to detect hemianopsia and quadrantanopsia. Examination of visual fields is generally carried out in neuroophthalmology through perimetry in a task in which the patient maintains his/her gaze on a fixed point and must detect the appearance of a stimulus in another part of the perimeter of the visual field. The patient must therefore simultaneously perceive two points. After certain injuries to the occipital cortex, the ability to perceive two points simultaneously is impaired and such patients can only perceive one stimulus at a time. However, it is important to take into account that the results of visual field perimetry testing may be affected by attentional problems. In such cases, mistakes may be more determined by the attentional disorder than by visual field problems.

Another important part of the neuroophthalmological examination is the examination of eye movements and of the direction of the gaze, especially the elementary or reflex movements and the complex or psychomotor movements. The reflex movements examined here consist of a reflexive tendency to fix and follow the gaze on a point or object situated in the central visual field as the object moves to the right or to the left. This type of eye movement is associated with the lower part of the brain stem and the cortical posterior oculomotor centres. The psychomotor movements are studied in a more complex task, in which, for example, the patient must move the gaze to the opposite side of the object as the object remains in the visual field. These movements are associated with the anterior oculomotor centres of the brain and to the anterior zones of the frontal lobes which connect to these oculomotor centres. The examination of eye movements may be done clinically as well as by means of different electroencephalographic methods.

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