Why does prosopagnosia (face blindness) only affect recognition of faces?

Question

I read a short story involving prosopagnosia (Wikipedia), which harms or fully removes a person's ability to remember and recognize faces, and I've since been doing reading to better understand the condition. The precise causes, as I understand it, are not well-known, although it is believed to be related to damage in the right fusiform gyrus:

Prosopagnosia is thought to be the result of abnormalities, damage, or impairment in the right fusiform gyrus, a fold in the brain that appears to coordinate the neural systems that control facial perception and memory.

^NIH

As far as I'm aware, the fusiform gyrus has functions beyond facial recognition and analysis - although my knowledge of how facial recognition in the brain works is limited. Therefore, my naïve logic is that damage to the region should also damage other (related) mental abilities, yet I can't find much information about other disabilities prosopagnosiacs may face, if any.

If prosopagnosia does arise from damage to the fusiform gynus, why are the effects merely limited to facial perception? If the effects are not this limited, are there any minor disabilities associated with the condition?

Answer 1

Simply put, it doesn't.

Breaking the word prosopagnosia down you end up with:

Prosop is rooted in Greek for face, and gnosis is knowledge (agnosia is therefore lack of knowledge, or ignorance, but not in a pejorative sense).

There are tons of agnosias, which is defined as impairment of a single modality (like vision) from being able to process information correctly. As Bill Oertell's answer correctly points out, his pattern recognition skills are impaired visually and affects faces, birds, and I'm sure other similar objects. I'd imagine things with similar and subtle color changes (like hawks and human faces) cause issues.

Further, something like dementia can impact facial recognition which is a subclass called developmental prosopagnosia, and that obviously carries a host of other impairments.

Prosopagnosia is a disorder that can be caused by trauma, genetics from birth, and developmental conditions. It is a symptom, not a cause, and as such the cause will generally exhibit other symptoms as well.

Answer 2

Face blindness is typically associated with a loss of "map memory" as well, an inability to memorize the layout of some place and find your way around.

Oliver Sacks describes this:

https://www.newyorker.com/magazine/2010/08/30/face-blind

I have both disabilities, apparently due to a case of polio at age 21 months.

Oddly, the condition appears to affect "formula memory" in me, meaning I can't readily recall "cookbook" solutions to programming problems. Happily, this forces me to invent new solutions, and I've invented several in my career which were at least modestly notable.