Patient DF: A Case of Visual Agnosia
CASE STUDIES
Sophia Perez
7/27/20263 min read
Most people, when given an object such as a pencil, are usually aware of how to use it. At first glance, they see a wooden stick with a sharp tip and a dull end. They know that they have to hold it with their dominant hand and use the sharp tip to write with, while the other side, which comprises a rubber eraser, is used for erasing mistakes and accidental markings. But what happens when you suddenly become unable to give a name to the object you are holding in your hand?
Patient DF is one of the most popular cases in neuropsychology, which exhibits one of the best examples of Visual Form Agnosia. Before her condition, she was described as a healthy 34-year-old female who had no prior neurological problems or illnesses, she led a normal life as a housewife with normal brain function. Though, an accidental poisoning incident changed everything. In 1988, just days after her 34th birthday, she was exposed to Carbon Monoxide (CO): a colorless, odorless, and tasteless gas. This happened due to her using a faulty water heater while showering in her newly renovated cottage. When it is inhaled, CO enters your bloodstream and prevents vital organs like the brain from getting the oxygen they need, a condition also known as hypoxia. She was also pronounced to be in a coma and doctors found permanent brain damage.
From the moment she woke, Patient DF was found to have profound initial symptoms, including what is known as Visual Form Agnosia. This condition is characterized by the inability to visually name and recognize common objects, letters, or shapes, yet the ability and function of other sensory functions such as touch and hearing are still intact. This case shows how even the smallest of wrong decisions, such as taking a shower with unseemingly faulty equipment, can lead to disastrous and most often, life-altering consequences.
The Brain’s Visual Pathways
Vision is divided into two major pathways, which align with the Two-Streams Hypothesis: the Ventral and the Dorsal processing streams. The Ventral Stream is known as the “what” stream, it is strongly connected to the medial temporal lobe (for long-term memories) and the limbic system (emotion control). It is primarily responsible for visual and auditory identification and object recognition.
The Dorsal Stream, on the other hand, was proposed to be involved in guiding actions and recognizing “where” objects are in space. It was initially called the “where” stream as it was hypothesized that the dorsal stream processes information with regards to the location of the object. However, it was later discovered that it is actually responsible for processing visual information needed to understand an object’s location, movement, and how to physically grab or manipulate it.
Together, these two pathways work together to do daily tasks, through identifying objects (ventral stream), and processing how to use it (dorsal stream).
What Happened in DF’s Brain?
In the case of Patient DF, her agnosia was seen to be caused by damage in the lateral occipital cortex (LOC), which is the part of the brain which houses the brain’s visual pathways. In this case, her Ventral Stream was silenced, leading to her being unable to identify common objects, shapes, and letters. She was also unable to recreate drawings or guess the width of objects.
Though, her Dorsal Stream remained intact – allowing her to interact with objects and understand how to hold and use everyday objects. She could still drop letters inside mailboxes and grasp objects correctly. This striking phenomena revealed to scientists that perception of objects and understanding of their use, are controlled separately, leading to the two-streams hypothesis of vision.
Why This Matters Today
DF’s case became a great piece of evidence for the two-streams hypothesis in vision. It has enabled neuroscience to further understand recognition and the living conscience. It matters today because:
It has led to further implementations of rehabilitation therapy for patients suffering the same conditions, by leveraging the intact pathway to the patient’s advantage.
It has helped doctors to further understand the difference between perception deficits (ventral) and action deficits (dorsal) in patients with brain injuries.