From PumkinPerson: Some thoughts on the nature of intelligence:
Verbal IQ (using your vocal cords as a tool to your advantage), and Performance IQ (using your hands as a tool to your advantage). So Verbal IQ measures abilities such as vocabulary, and Performance IQ measures largely spatial abilities such as making designs using multi-coloured blocks.
However if the human mind were placed in the body of a snake, our Verbal IQ would be virtually useless because we’d have no vocal cords with which to speak,
Pumpkin may be conflating ‘talkiness’ with verbal IQ as measured by the verbal portion of the SAT or the verbal part of an IQ test. Although verbal ability (such as vocabulary, reading comprehension, and writing ability) and speech are related, the proficiency or verbosity in the later doesn’t necessarily strongly correlate with competence in the former. People who score well on the verbal part of the SAT, especially the hard pre-1995 version, tend to be very intelligent, but highly intelligent people tend to not be gregarious and extroverted, whereas talkative people with good social skills may score low on the verbal part of a standardized test, and a low score doesn’t inhibit their ability to vocalize. Verbal IQ can be acquired by reading as opposed to talking. The Ferguson protectors are quite vocal, but do they have a high verbal IQ? No.
Studies show that deaf children score poorly on verbal portions of IQ tests. Since, early in life, reading and phonics are linked, children who are deaf are deprived of this crucial auditory learning process, hence low verbal-IQ scores. Perhaps people who become deaf later in life have a higher verbal IQ than the congenitally deaf, since the former picked up the fundamentals before becoming deaf. This could explain how introverts, who tend to be taciturn, can perform very well on verbal portions of IQ and standardized tests, and is evidence that there is more at play in verbal IQ than just language and talking.
What is the antecedent of verbal IQ? Probably, g, a catch-all for generalized intelligence. People with high generalized intelligence tend to be better at all aspects of intelligence, with strengths and weaknesses in different subsets, but overall above average ability. Working memory, such as the ability to retain information, can lead to a superior verbal IQ because people with strong working memories read faster, more efficiently, and retain more of the words they read, leading to a high crystallized IQ as well. Processing speed, a subset of performance IQ, is also important for verbal IQ since people who process words faster will have richer vocabularies.
I also expect a positive correlation between non-verbal IQ and verbal-IQ, even among deaf subjects, and such a correlation does indeed exist. From human varieties, The study of deaf people since Braden (1994):
Slate & Fawcett (1995) report a high correlation between WISC-III performance scale and WISC-R performance scale (0.93) in a sample of 47 deaf students (but 43 students over a 3-year time period). The correlation between WISC-III PIQ with WRAT-R Reading, Spelling and Arithmetic subtests are 0.41, 0.48, 0.64, respectively. The respective numbers for WISC-R PIQ are 0.43,0 .45, 0.68.
WISC-III = an IQ test for children
WISC-R = an older version of the above test
PIQ = performance IQ, non-verbal
WRAT-R = a subject-based test with Reading, Spelling and Arithmetic subtests
And from a meta study
First, as the severely hearing-impaired are a language-deprived group and performance IQ tests are in essence cognitive tasks, the implication follows that level of language development may not be related to cognitive functioning. The logic of this position is that the deaf, a language-deprived group, score as well as the controls who have normal language development. A more thorough examination of this serendipitous interpretation of these data is in print (Vernon, 1967b).
Second, it has been noted that deaf children, a group with severe cultural deprivation due to lack of experience with language, do as well on performance IQ tests as normal hearing children without this deprivation. The implication is that cultural deprivation may not play the role currently being ascribed to it in the development of intelligence.
This lends credence that language is independent of generalized intelligence. So it would seem like there is a mechanism (not intelligence) early in life that leads to the development of language (the fundamental), and these building blocks later play an important role in verbal IQ. Those with higher IQs, beyond knowing the fundamentals, are more efficient at information processing (generalized IQ), hence a higher verbal IQ.