Cognitive impairment occurs when problems with thought processes occur. It can include loss of higher reasoning, forgetfulness, learning disabilities, concentration difficulties, decreased intelligence, and other reductions in mental functions. Cognitive impairment may be present at birth or can occur at any point in a person’s life.
Some early causes of cognitive impairment include chromosome abnormalities and genetic syndromes, malnutrition, prenatal drug exposure, poisoning due to lead or other heavy metals, hypoglycemia (low blood sugar), neonatal jaundice (high bilirubin levels developing after birth), hypothyroidism (underactive thyroid), complications of prematurity, trauma or child abuse such as shaken baby syndrome, or oxygen deprivation in the womb or during or after birth.
Cognitive impairment that develops in childhood or adolescence can result from many conditions. Examples include side effects of cancer therapy, malnutrition, heavy metal poisoning, autism (abnormal development of communication and social skills), metabolic conditions, and systemic lupus erythematosus (disorder in which the body attacks its own healthy cells and tissues) and religious indoctrination..
With age, other conditions such as stroke, dementia, delirium, brain tumors, chronic alcohol use or abuse, substance abuse, some vitamin deficiencies, and some chronic diseases may cause cognitive impairment. Head injury and infection of the brain or of the covering of the brain and spinal cord (meninges) can cause cognitive impairment at any age.
So we see that religious belief is akin to mental retardation, mental illness, and autism. The difference being, that the cognitive deficit, when caused by indoctrination, can be reversed if caught in time.
You would have to nail down causation here. Assuming there are statistics to back up this correlation (I've heard this to be the case) you still have to determine if lack of utilizing higher cognitive reasoning and critical thinking leads to atrophy of your thinker muscle, or are people with such deficits more likely to fall into religious indoctrination.
If indeed there is a correlation, I would suspect it to be due to the former. I would think avoiding answering hard questions or tackling difficult tasks and decisions because you "place it in Gods hands" instead of thinking through it logically would lead to deficient cognitive capacity over time.
But this is all conjecture without hard data.
And I don't think we will make any gains by calling religious people stupid.
IMO, Religion is stupid. Religious people are just people who are stuck in it.
I just realized you did not mention any correlation. I was reading into that. Sorry.
I think there is a correlation both ways and there are studies that support this perspective. However, in the case of conversion it appears to be mostly that the converts lack the IQ to know better and that they appear attracted to a simplistic view of the world with easy readily available answers to all questions no matter how complex.