In the days of old, deafness was arguably a fate worse than death, since it left you unable to produce or understand speech. It also must have reduced fitness to near zero, for those who care about such things.

Today, with deaf education and sign language, it’s a lot better. But it’s still not good.

Deaf adults have poor reading levels (~4th grade, on average), are far less likely to graduate from high school and college, and have a tough time making a living. Their unemployment rate is at least 40%, and seems to be getting worse with time. There used to be some blue-collar jobs that they fit pretty well, but those have become scarcer.

Severe congenital deafness hits about 1 in 1000 children. Some cases are caused by various environmental insults, but most are genetic. One particular mutation (GJB2 35delG) accounts for a fair fraction of genetic deafness (and almost certainly confers some kind of heterozygote advantage), but mutations in many different genes account for the majority of cases. Prenatal rubella used to cause a lot of cases, but that ended when there was an effective vaccination campaign back in the 1970s.

Because of the diverse mutational spectrum, > 90% of the children of deaf couples can hear. Many deaf people wish that their children were deaf like them, but they’re wrong, of course.

I was wondering about the language skills of those hearing children with deaf parents. It seems as if it might well be a disadvantage, but then kids are flexible and robust. We know that typical between-family variation doesn’t have much effect on adult IQ: but on the other hand, parents who can’t talk are pretty far from typical. I dug around, looked at a number of studies, but I’m not sure what the real story is. A lot of them were small-N, statistically useless – someone wrote about three kids. Sheesh. I got the strong impression that some of the articles were motivated: they didn’t want to give the impression that  having deaf parents was bad for a kid, even if it were true. Still, that doesn’t mean that they’re necessarily wrong.

Then the light dawned. Or, more accurately, the sun set. If the hearing kids of deaf parents don’t suffer a disadvantage in language development, it’s hard to see how the currently fashionable idea that lower verbal skills in black kids are caused by parents who don’t talk or read to them enough can be true. Yet it must be. And if they are disadvantaged, then that disses deaf parents – and that can’t be right. Does not Compute!

This happens a lot.

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44 Responses to Deafness

  1. Pingback: Daily Linkage – March 26, 2013 | The Second Estate

  2. Elegant proof. I can dig up some references, but I think that there is general acceptance that the effects of deafness and blindness in parents are different from the presumed effects of Black parenting.

  3. g2-337af867fe9cd20258bdbc586fbefd0d says:

    Only 35% of the children of deaf parents ever learn sign-language. The jobs for sign-language translators (police, courts, social workers, civil service, etc.) are filled by hearing adults that learn the language in special schools as a profession. That is in Israel.

  4. g2-337af867fe9cd20258bdbc586fbefd0d says:

    (Excuse me if I’m unable to work out if the above supports or not your thesis. Last night we celebrated Pessach, a religious ceremony where we are ordered to get drunk).

  5. CJPB says:

    That’s because, as outlined in Judith Rich Harris’ The Nurture Assumption, children don’t learn languages from their parents, but from their peers. That’s why even first generation immigrants will speak the local language (and dialect) of their area they immigrate to, unless they live in very isolated communities like the Amish.

    • JayMan says:

      Well, more accurately, children first learn language from their parents/older siblings, but then that is supplanted by what they acquire from their peers.

    • gcochran9 says:

      I didn’t think much of her book.

      • Pincher Martin says:

        What didn’t you like about it?

        • gcochran9 says:

          The fact that parents don’t much shape personality or cognition I already knew: but eliminating that hardly proves that peers do. I thought that she didn’t make much of a case.

      • fnn says:

        I hope you expand on that some day.

      • JayMan says:

        Interesting. Now I’m curious as to why. As I noted, I’m not so sold on the peer effect for reasons similar to what misdreavus lists. In No Two Alike, her general thesis however was that peer interaction amplify initially small differences between children (magnifying small differences between identical twins caused by developmental noise, for example). There was one study she did cite in that book that seemed to suggest peer interactions do have an effect (a smallish one). That study and a couple others have been banging around in my head for awhile, because I wanted to take a close look at where the research stood on definitively non-genetic influences on behavioral traits.

  6. winestock says:

    There was a Finnish saying that I used to hear from Ilkka Kokarinen. “The hunter does not see the mountains while chasing the rabbit.” Of course, in this case, they have. One would think that they would have second thoughts or at least call it a “paradox,” but no. Crimestop.

  7. unladen swallow says:

    What would be the genetic advantage conferred a weakened deafness mutation?

    • gcochran9 says:

      Too incoherent. Rephrase.

      • Portlander says:

        I suspect the question was regarding “(and almost certainly confers some kind of heterozygote advantage),” whether you could/cared to speculate on what any potential advantages might manifest as.

      • unladen swallow says:

        You said a particular mutation accounts for a moderate percentage of deafness, but almost certainly confers a heterozygote advantage. What advantage would you gain from having a mutation for deafness in a weakened form?

        • gcochran9 says:

          A heterozygote, or carrier, has one copy of the 35delG mutation, rather than two, as in a homozygote. Carriers aren’t deaf: homozygotes are. This has nothing to do with a ‘weakened form’.

          The carrier frequency in Europe ranges from 2-4%, so the gene frequency ranges from 1-2%. Since it was effectively lethal in homozygotes, there must have been a carrier advantage equal to the gene frequency, assuming equilibrium.

          No way you’d ever see this happen by chance in a large population.

          Carriers seem to have significantly thicker skin. Intestinal cells with mutations are resistant to invasion by shigella flexneri. Looks like a disease defense.

  8. misdreavus says:

    The fact that The Nurture Assumption was even controversial among psychologists attests to the pitiful state of knowledge in the human sciences. So parenting truly exerts no long term effect over intelligence and personality? Those of us acquainted with behavior genetics knew as much already.

    But if you ask me, the second half of Harris’s argument was singularly uncompelling. Peer influence may explain some short-lived similarities in behavior between children of the same cohort, and might also serve as a likely mechanism for the transmission of certain elements of culture. It does a terrible job explaining why Julian is smarter than Danny, or why Sally is more outgoing than Jill.

    • JayMan says:

      Harris made a fantastic case for why parenting leaves no long term impact on IQ and behavioral traits. The peer part I’m not completely sold on, however. For one, there’s usually no way to distinguish cause and effect in peer association. If kids who smoke tend to roll together, for example, then how do we know that they smoke because of mutual influence or if the smokers just managed to find each other?

      Harris recognized a lot of the limitations in her theory and expanded on it in her next book No Two Alike. Still only limited support for the peer part, but a pretty good analysis of what’s going on with the non-genetic component to the variance in behavioral traits (particularly, the role of developmental noise).

      • misdreavus says:

        I am aware of her second book, but I just can’t bring myself to read it, not with so many other distractions vying for my limited attention. 🙂

        Like I said, peer influence surely explains similarities between children, and perhaps serves as the most important vehicle for the transmission of cultural norms. Harris is right that upper class English children at Eton don’t learn how to behave like gentlemen by imitating their parents. Neither do the children of immigrants learn their primary language by doing the same. But behavioral *differences* between children are the stuff of developmental psychology – everything else is useless speculation or armchair rhapsodizing, because the pertinent experiments can only be conducted in the here and now.

      • JayMan says:

        Harris makes a much better and much more plausible case in No Two Alike, in which she admits that her ideas for how differences in children emerge that she put forward in her first book were weak. However, despite a few studies that suggest small effects here and there, the general problem is there is no way to know how much of the difference between children (symbolized by the difference between MZ twins raised together) that isn’t due to genetics isn’t simply due to developmental noise, or to plain old randomness.

  9. yeah – and people like Annie Murphy Paul are still harping on about the incredible importance of the between-family environment

  10. Jason Malloy says:

    “I was wondering about the language skills of those hearing children with deaf parents. It seems as if it might well be a disadvantage, but then kids are flexible and robust”

    The deaf-black comparison seems like a fruitful line of inquiry, but it sputtered out in the early 1990s. Leon Kamin’s rejoinder in Intelligence only has six citations, and none add further data or arguments. So I’ll just relay what he says:

    There is no intelligence deficit in deaf children with deaf parents, only in deaf children with hearing parents. Presumably the brain adapts and processes visual sign language just as it would aural language, so if the two are used in an equivalent manner from a young age, there is actually no developmental disadvantage. (And likewise if children are not exposed to some kind of language at developmentally critical junctures, this can have lasting consequences on normal intellectual development).

    So hearing children of deaf parents should have normal intelligence, since deaf children of deaf parents allegedly have normal intelligence.

  11. Jason Malloy says:

    By the way, here’s a related abstract from the 2007 meeting of the International Society for Intelligence Research. It was apparently never published, and this can’t be found online, so I’ve uploaded it:

    Blindness, Deprivation, and IQ: A Meta-Analysis
    … The present study performed a meta-analysis of studies of the IQ of visually impaired children and adults. The results of our analysis demonstrated that visual deprivation showed no effect on the average IQ scores of a severely handicapped group, and therefore it disconfirmed the cumulative deficit hypothesis … Further, the fact that the severely deprived environment of visually impaired has no impact on their average IQ score makes it less likely that the arguably less deprived environment of, for instance, Blacks in the U.S. or immigrant groups in Europe is the cause of their lower mean IQs. Our meta-analytically based study makes environmental causes of group differences in IQ less plausible and therefore genetic causes less implausible.

  12. Matt says:

    Interesting. I would have though blindnesses would influence strongly visual-spatial tests, and thus on IQ like abilities which involve even some degree of abstract spatial representation and are spatially linked (e.g. mathematics).

    It would be interesting to know if they got around this by controlling so that anything which factored / clustered even slightly with primary spatial abilities (like mental rotation) or whether it really is the case that they included lots of abilities which included primary spatial or visual abilities, in which case it is surprising to me that they would still perform similarly with no visual experience. Are they giving these people Braille Raven’s Matrices of something? Giving them objects and asking about rotations without letting them turn the thing to test?

  13. g2-337af867fe9cd20258bdbc586fbefd0d says:

    Prof. Jan te Nijenhuis in analyzes the increase in IQ by training. “The findings show that not the high-g participants increase their scores the most – as is common in training situations – but it is the low-g persons showing the largest increases of their scores.” I interpret this as training does improve IQ scores and moreso for the stupidest segment of humanity. Therefore they should be educated, so their IQ and earning ability improves, although the improvement will be “hollow” as it does not change their general intelligence. On the other hand, training and education does little to improve smart people. Special education for hearing children of deaf parents is unnecessary (as I think Prof. Cochran implies) but investment in special training of African children is productive as it will help them in performing non g-charged jobs.

  14. I can recall Jan te Nijenhuis presenting his paper in Amsterdam in 2007, and I thought it was an important contribution. Others did not. Nonetheless, I think that his observations damage the notion that low ability in children is primarily due to low intellectual stimulation from their parents, absent really abusive parenting.

  15. Dr. Jan te Nijenhuis from the University of Amsterdam, a well-known intelligence researcher, asked me to post this comment.
    “Inspired by Jefferey Braden’s brilliant book on the IQ of the deaf two of my hardworking undergraduate students at the Univeristy of Amsterdam carried out a huge meta-analysis of the IQ scores of the blind. We found 72 studies for our meta-analysis, so it is a huge one. Quite a few studies test ALL blind children in a country, so you have the complete population and not a sample, allowing strong conclusions. A fascinating finding is that blind adults tested with the verbal parts of traditional IQ tests – sometimes read to them – have a mean IQ score of close to 100, just as sighted persons. So, for instance, in the US adult blind Whites have an IQ of 100 whereas sighted adult Blacks have an IQ of 85.
    I want to submit this research for publication in a high-impact journal but there are still loose ends I am busy tying up. I definitely want to publish this. I already received quite a few highly positive comments on my 2007 ISIR presentation on this topic. ”

  16. FD says:

    I think you’ll find that the argument for the importance of exposure to a linguistically rich environment for a child’s language skill development to be robust, both theoretically and empirically.

  17. Steve Sailer says:

    “the currently fashionable idea that lower verbal skills in black kids are caused by parents who don’t talk”

    Obviously, black kids don’t get exposed to enough talk, which explains why there are so few black rappers.

  18. mindswarm says:

    @Cochran: Have you heard of the anti-Cochlear movement?

    Much of the strongest objection to cochlear implants has come from the deaf community, which consists largely of pre-lingually deaf people whose first language is a signed language. For some in the Deaf community, cochlear implants are an affront to their culture, which as they view it, is a minority threatened by the hearing majority…. [To be most effective, cochlear implants are] implanted at a young age, during the critical period in which the brain is still learning to interpret sound. Hence they are implanted before the recipients can decide for themselves, on the assumption that deafness is a disability. Deaf culture critics argue that the cochlear implant and the subsequent therapy often become the focus of the child’s identity at the expense of a possible future deaf identity and ease of communication in sign language, and claim that measuring the child’s success only by their mastery of hearing and speech will lead to a poor self-image as “disabled” (because the implants do not produce normal hearing) rather than having the healthy self-concept of a proudly deaf person.

    • gcochran9 says:

      Sure, I’ve heard of it. To the extent that cochlear implants are risky or ineffective, one can argue against them. As for all this ‘identity’ stuff, that’s just nonsense.

    • teageegeepea says:

      I’ve seen cochlear implant videos of adults hiring for the first time. I wasn’t aware some can’t distinguish speech if they get it as adults. The claims in the Wikipedia article are marked as needing citations though.

  19. DeafGuy says:

    I’m 45 years old and severely hard of hearing (85 dB loss on the left, 115dB on the right). My hearing loss is congenital, but progressive with onset at puberty (my hearing was normal at birth). It has been highly heritable in my family, probably linked to sites on the Y Chromosome since it only seems to affect male carriers. Our hearing loss is primarily neurological. I have noticed among my relatives who share this curse that it seems to be associated with a specific constellation of traits to greater or lesser degree: low latent inhibition, high cognitive focus ability, high anxiety and/or obsessive personalities, balanced cognition (while only a few of us are truly ambidextrous, most are right handed and left-eye dominant with significant off-hand dexterity, and several of us have been strong baseball switch hitters), high sensitivity to heat/cold, very high tactile sensitivity, very high visual acuity that remains stable late in life, and very high spatial reasoning ability. As a professional architectural designer, I’ve put many of these to best advantage in my career. No offers from the Yankees yet though, and I’ll never be able to drink my coffee hotter than tepid without literally blistering my mouth.

    My generation has been fortunate that our deafness has been offset by parallel advances in hearing assistance technology and the widespread adoption of electronic text-based communication. My hearing aids are so good that most people don’t realize that without them I am effectively a deaf person. Phone conversations are still a bit problematic though. Context and visual cues are essential to understanding.

    A study of deafness and cognitive abilities would be very interesting, I think. Most people have a tendency to associate the behavior of deaf and hearing impaired people as stupidity (misunderstanding simple things, constant conversational non sequitors, etc.). Hearing impairment has a very high negative correlation with socioeconomic accomplishment. The elevated incidence of Alzheimer’s among the deaf and HoH is also of interest.

    At any rate, this rambling comment is meant to encourage you in exploring this subject as fertile ground in cognitive traits and heritability. I think it’s grossly under-developed as a scientific area, and there are opportunities for controlled study that are rare elsewhere.

    • gcochran9 says:

      They just identified the cause of a Y-linked deafness syndrome a couple of months ago. A chunk of chromosome 1 miscopied onto the Y chromosome.
      I don’t know if that’s what you have or not – it’s only been found in China.

      Yeah, deafness is a potentially useful natural experiment, but there are a lot of things we don’t want to understand.

  20. Jason Malloy says:

    Not sure how much you care, but here’s a Polish language study that might have some useful data.

    Pietrulewicz, B. (1979). [Intelligence of hearing children reared by deaf parents]. Psychologia Wychowawcza, 22(3), 393-400.

    The University of Illinois at Urbana-Champaign web catalog says it has volume 22, issue 3 of this journal, but my unpredictable interlibrary loan service won’t fetch it for me. Maybe you use a more reliable University file service.

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