Visual Perception - what it exactly is?

Visual perception is the ability to interpret and use what is seen. Interpretation is a mental process involving cognition, which gives meaning to the visual stimulus. Visual perception could also be defined as total process responsible for the reception and cognition of visual stimuli. The visual receptive component is the process of extracting and organizing information from the environment and the visual cognitive component is the ability to interpret and use what is seen. These 2 components allow us to understand what we see, and are both necessary for functional vision.

Visual perceptual skills include recognition and identification of shapes, objects, colors, and other qualities. With the help of visual perception a person makes accurate judgments of size, configuration and spatial relationships of objects.

The interactions of visual-receptive and visual-cognitive components help in the following functions:

·         Respond and adjust to retinal stimuli (anatomic and physiologic integrity)

·         Move both the head and eyes to collect raw data (occulomotor and vestibular control)

·         Effectively interpret visual information (visuo-perceptual ability)

·         Respond to visual cues through efficient limb movements (visuo-motor ability)

·         Accomplish integration of all these abilities.

The components of visual perception could easily be explained with the following flowchart:

Visual- receptive components include fixation, pursuit and saccadic eye movements, acuity, accommodation, binocular vision and streopsis and convergence and divergence.

• Visual fixation is fixing one’s gaze on anything. This and movement of eyes is done with the help of 6 extra-ocular muscles. Two types of eye movements are used to gather information from environment: pursuit eye movement (tracking) and saccadic eye movements (scanning). Visual pursuit involves the continued fixation on a moving object while Saccadic eye movements are rapid change of fixation from one point to another in visual field.

• Acuity – capacity to discriminate fine details of objects in the visual field.

• Accommodation – ability of each eye to compensate for a blurred image. It is the process used to obtain a clear vision i.e. focus on an object at varying distances. The internal ocular muscle (ciliary muscle) contracts and causes a change in crystalline lens to adjust for objects at different distances.

• Binocular fusion – ability to mentally combine images from 2 eyes into single percept.

• Streopsis – binocular depth perception or 3-D vision.

• Convergence or divergence – ability of both eyes to turn inwards towards the medial plane and outwards from the medial plane.

Visual cognitive components include visual attention, visual memory, discrimination and integration of visual stimulus with other sensory modalities.

·         Visual attention is focusing on one part of the visual field while ignoring others. The 4 components of visual attention are alertness, selective attention, vigilance and shared attention. Alertness reflects natural state of arousal. Alerting is transition from an awake to an attentive and ready state needed for active learning and adaptive behavior. Selective attention is ability to choose relevant visual information while ignoring less relevant information; it is conscious focused attention. Visual vigilance is conscious mental effort to concentrate and persist at a visual task. Divided or shared attention is ability to respond to 2 or more simultaneous tasks.

o   Deficit in the area of visual attention in a child is usually manifested as easy visual distractibility. He/she would not be able to focus on one object in environment and would get distracted while trying to focus on everything at one time. He will find it hard to maintain his gaze on the task at hand and would consistently look at other objects without staying at one for long.

·         Visual memory: it involves integration of visual information with previous experiences. Long-term memory is the permanent storehouse which has expansive capacity; while short term memory can hold a limited number of unrelated bits of information for approximately 30 seconds.

o   A child having deficit in this area will have difficulty in comprehending long sentences as he tends to forget the initial words of the sentence read by the time he reaches the end of sentence. Also copying from blackboard is troublesome for him as he ll forget what was read in the time it took him to read what’s written and shifting gaze from blackboard to copy.

·         Visual discrimination: ability to detect features of stimuli for recognition, matching and categorization. Recognition is ability to note key features of a stimulus and relate them to memory. Matching is ability to note similarities among visual stimuli. Categorization is ability to mentally determine a quality or category on which similarities or differences can be noted.

§  Object (form) perception

                                            i.  Form constancy – recognition of forms and objects as the same in various environments, positions and sizes. It helps a person develop stability and consistency in visual world. It enables a person to recognize objects even with differences in orientation or detail, and to make assumptions regarding the size of an object even though visual stimuli may vary under different circumstances (a school age child can identify the letters whether they are in type, written in many script, cursive, italics or written in upper or lower case letters).

                                          ii.  Visual closure – identification of forms and/ or objects from incomplete presentations. It enables person to quickly recognize objects, shapes, and forms by mentally completing the image or by matching it to information previously stored in memory (a child working at his/her desk is able to distinguish a pencil from a pen, even though both are partially hidden under some papers)

                                        iii.  Figure-ground – the differentiation between fore ground and background forms and objects. It is ability to visually attend to what is important; separating essential important data from distracting surrounding information.

·         Spatial perception

                                            i.  Position in space – determination of spatial relationship of figures and objects to oneself or other forms and objects. It is important to understand directional language concepts such as in, out, up, down, in front of, behind, between, left and right. It provides ability to differentiate letters, and sequences of letters in a word or in a sentence (child knows how to place letters equal spaces apart, touching the line; he/she is able to recognize letters that extend below the line such as “p,g,q,y”)

                                          ii.   Depth perception – determination of relative distance between objects, figures, or landmarks and the observer and changes in planes of surfaces.

                                        iii.  Topographical orientation – determination of location of objects and settings and route to the location.

·         Visual Imagery : also called visualization. It is ability to “picture” people, ideas and objects in the minds eye, even when objects are not physically present. Visual-verbal matching provides foundation for reading, comprehension and spelling.