Agnosia is a rare condition characterized by difficulties recognizing or perceiving familiar objects, people, or sounds due to sensory processing deficits. It primarily affects one’s ability to understand what they see, hear, or touch.

Generally, only one of the senses (vision, hearing, or touch) is affected. Therefore, individuals with agnosia are often able to utilize their other senses to compensate and improve their quality of life. However, there are also ways to improve one’s ability to process stimuli and regain affected functions.

Causes of Agnosia

Difficulties with recognition in individuals with agnosia are unrelated to memory, attention, or other cognitive problems. Instead, agnosia is caused by damage to the areas of the brain responsible for sensory processing, such as the posterior cortex and occipitotemporal regions.

Agnosia can develop following various neurological conditions, including:

• Stroke
• Tumor
• Infection
• Dementia
• Hypoxia
• Toxins
• Head injury
• Developmental disorders

Although agnosia affects one’s ability to recognize or perceive sensory information, the senses themselves function normally. For example, individuals who cannot recognize what they see are not experiencing a problem with their eyes. Rather, they’re experiencing a problem with the way the brain processes what their eyes see.

Depending on which areas of the brain are affected, individuals may experience a wide variety of symptoms. In the following section, we’ll differentiate the various types of agnosia.

Types of Agnosia

Agnosia affects the way the brain processes what you see, hear, or touch, but it generally only affects the processing of one of these senses.

Below, we’ll discuss the differences between visual, auditory, and tactile agnosias.

Visual Agnosia

Visual agnosia refers to difficulties recognizing what you see despite being able to see clearly. For some, certain types of objects may be more difficult to recognize than others.

Visual agnosias are the most common and best-understood type of agnosias. They can be further classified as apperceptive or associative.

Apperceptive agnosia refers to impairments caused in the early stages of visual processing when the brain gathers visual stimuli into an image. Individuals with this classification of agnosia may struggle to match two identical objects; however, they are often able to verbally identify how the objects appear (the color, texture, etc).

In contrast, associative agnosia describes the inability to assign meaning to images. Individuals with this type of agnosia can often draw, match, or copy what they see; however, they struggle to match different categories or presentations of a stimulus. For example, they may not be able to match a mechanical pencil to a wood pencil, or a closed umbrella to an open one. Additionally, individuals with associative agnosia struggle to name the objects they are looking at.

Types of visual agnosias include:

• Prosopagnosia describes difficulties recognizing familiar faces. However, individuals are usually still able to identify other aspects of a person such as their gender, hair, and clothing.
• Simultanagnosia describes difficulties seeing more than one object at a time when they are grouped together.
• Color agnosia describes difficulties distinguishing between colors.
• Topographical agnosia describes difficulties interpreting spatial information, resulting in difficulties with navigation using visual cues.
• Finger agnosia describes difficulties differentiating between fingers.
• Akinetopsia describes the difficulties perceiving motion. Most people with this condition see moving objects as a series of stills.
• Agnostic alexia describes difficulties recognizing written words visually despite being able to write and talk.

Auditory Agnosia

When an individual has auditory agnosia, they are unable to recognize or perceive what they hear. Although their hearing functions are normal, the brain struggles to assign meaning to or differentiate between sounds.

Types of auditory agnosias include:

• Phonagnosia describes difficulties recognizing familiar voices.
• Verbal auditory agnosia (pure word deafness) describes difficulties understanding spoken words. However, these individuals can typically read, write, and speak properly, which is what distinguishes it from some types of aphasia.
• Nonverbal auditory agnosia describes difficulties comprehending nonverbal sounds. For example, when they hear a car motor start, they would not associate it with an engine or car. However, they are still able to understand spoken language.
• Amusia describes the inability to differentiate music from other types of sounds.

Tactile Agnosia

Tactile agnosia refers to the inability to recognize or perceive touch. Individuals with tactile agnosia can feel what they touch; however, they often struggle to identify or differentiate what they are touching.

Types of tactile agnosias include:

• Amorphognosia describes difficulties identifying the size and shape of an object by touch. For example, you could not tell if an object is round or square just by feeling it.
• Ahylognosia describes difficulties identifying distinctive physical properties of an object such as texture and weight.

Now that you understand the various ways agnosia can present itself following a neurological injury, the following section will discuss management interventions and treatment.

Agnosia Treatment