Definition/Introduction

Visual discrimination is the ability to detect differences in and ability to classify objects, symbols, or shapes. These can be categorized by color, position, form, pattern, texture, as well as size. In the simplest terms, the eyes normally receive input from the environment, then various cells detect and transmit signals to the brain. For visual discrimination, specifically, the visual cortex, contained within the occipital lobe, is the area responsible for detecting the shape and orientation of objects. Three cell types in the primary visual cortex (simple, complex, and hypercomplex) display correspondingly increased ability to respond to motion and degree of linearity. A more in-depth explanation of the visual cortex is a separate neuroanatomy topic.[1]

The classification and categorization of vision form a basis for studying how humans receive and process visual stimuli. For example, a study of visual texture helps explain more complex connections between task modulation and perception.[2] Visual discrimination has intimate connections to other brain and body functions, including hearing, memory, motion, and ambulation.[3][4][5][6][7][8][9] Humans depend on learned visual and motion cues to interpret their surroundings.[10] Human performance can be examined through a visual lens. In sports, a study of gender differences in fencing identified both statistically significant similarities and differences in various visual capabilities.[11] In the arts, experimental data support that musicians have lower thresholds of discrimination for visual, as well as auditory and auditory-tactile stimuli.[12]

Visual discrimination should not be confused with visual acuity, which denotes the sharpness of visualization. Eye examinations can assess both using the traditional eye chart. (The patient identifies a letter or symbol, and determines how clear a letter or symbol at a distance.) Questionnaires can also help to assess a patient’s visual function.

Applications of technology should be studied to improve and assess relevant components of human visual function. Facial recognition, objectively measured using EEG, is more potent in the upright than in inverted orientations. This finding supports the human use of visual categorization and orientation.[13] Humans can also be compared to computers to assess the visual processing abilities of both. At present, prototypical and complex facial expression discrimination sensitivity of humans still outpaces artificial intelligence (A.I.) capabilities.[14]

Issues of Concern

Both changes and limitations in vision are of concern to the patient, and these issues span all stages of life. A significant amount of visual learning occurs in infants and young children.[15][16][17] Aging-related degeneration, as well as oncogenic processes, affect vision in a multitude of ways.[18][19][20][21][22] Vision is affected by both orbital tumors and tumors or other pathology affecting the optic nerve.

Sudden loss of vision or visual disturbances may indicate serious conditions, such as cerebral vascular accident (CVA). The loss of or a deficiency in visual discrimination specifically may have more subtle clinical connotations, such as increasing difficulty in discerning and describing the correct shape of a circular clock, over time. Any condition that affects vision as a whole may also affect visual discrimination. Essentially, a patient cannot visually categorize objects that they are unable to see.

Clinical Significance

Specific conditions that affect vision and present clinically will most commonly have neurological, degenerative, anatomic, or oncogenic etiologies.  For example, visual agnosia is the loss of the ability to recognize faces or objects.[23] It may occur secondary to traumatic brain injury (TBI), dementia, or neurodegenerative conditions, such as multiple sclerosis.

Tumors contribute to a variety of visual discrimination deficiencies.[24][25] Tumors can be difficult to identify and/or remove without affecting surrounding tissue, which may include the visual cortex or important visual pathways.[26] Brain tumors and ophthalmic malignancies often affect children, but their longitudinal effects can be measured into adulthood by examining retinoblastoma survivors, for example.[27][28]

Red-green colorblindness is the most common form of color, visual discrimination condition. It is predominantly seen in males as it is X-linked.[29] Red-green colorblindness occurs because of an absence or deficiency in cone photoreceptors of the retina. A simple exam, called a plate test, can identify different types and degrees of colorblindness. Eyewear can be used in some instances to help patients discern a broader range of colors.

A variety of visual discrimination effects are also seen secondary to:

• Diabetic retinopathy[30]
• Dyslexia[31]
• Lewy body disorders[32]
• ALS[33]  

This list is not all-inclusive; there are many more clinical examples of visual discrimination issues. Again, these conditions span all age groups, and a variety of primary causes or primary disease, leading to secondary visual effects.

Nursing, Allied Health, and Interprofessional Team Interventions

Many different types of diseases and deficits during development can cause visual discrimination disturbances. Practitioners need to be cognizant of and knowledgeable about when to refer a patient to a specialist for further examination and workup; this is especially true of Family Physicians and ophthalmologists, who are often the 1st to identify a visual issue in a patient.

Occupational/physical therapies are available for children to improve visual organization skills. Rehabilitation therapies are available for those with a traumatic brain injury (TBI) affecting the visual cortex. Newer methods of training athletes to improve performance are also more regularly employed.

Nursing, Allied Health, and Interprofessional Team Monitoring

Patients should receive screening for visual changes, disturbances, and deficiencies at any age. Problems are also identifiable during well-child visits or routine adult annual physical examinations.