Developing Intelligence

The word “noise” comes from the latin nausea, meaning disgust or annoyance. But in the phenomenon known as stochastic resonance, noise can actually be a good thing: it can serve as a signal amplifier in thresholded systems.

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This phenomenon is not nearly as arcane as it sounds. The image above (borrowed from Stein, Gossen & Jones, 2005), clearly shows how two very weak signals can look very similar (top row), but with additional noise, the characteristics of these signals can be more easily dissociated (bottom row; now you can see one signal is generated by a sine, and one generated by a square wave).

Some theories posit that “neural noise” may be precisely tuned to serve a similar function in the brain. We know that the brain is a noisy system, and that neurons themselves are thresholded, so the possibility seems alluring. On the other hand, too much noise might “drown out” the true signals, preventing their accurate extraction. There are also more complex reasons to believe that correlated noise (again, often observed in neural systems) can have unexpected effects on information processing efficiency (based on information theoretic analyses). Together, these factors require that if noise is used adaptively to create stochastic resonance in neural circuits, the noise itself would require rather precise tuning.

These arguments focus on noise that is intrinsic to the brain. However, some recent work has shown that even environmental noise can have some positive benefits on the disordered cognitive system, perhaps by “retuning” maladaptive noise levels by introducing noise to the brain through the perceptual system, and thereby improving stochastic resonance phenomena.

In a doctoral dissertation (and now a newly published paper), Göran B. W. Söderlund describes how high intensity, broadband noise may actually alleviate some of the distractibility inherent to disorders like ADHD. Interpreted loosely, the idea is that those with ADHD are chronically understimulated by both their environment and their internal cognitive representations, leading them to search almost incessantly for more stimulating things (environments or thoughts), which takes the behavioral form of distractibility. This chronic cognitive understimulation might be overcome by introducing additional noise to the cognitive system through the perceptual system.

To test this idea, 42 children (21 with ADHD) between 9 and 12 years of age completed both a low-load and a high-load memory task. These tasks were fairly unusual as memory tasks go: they involved subjects listening to a series of actions (and then performing them in the low-load condition) and then recalling them after a delay period. Each subject completed both task under conditions of no noise, or 80 db white noise.

The results showed that children with ADHD improved on their recall in the low-load task, whereas noise had no effect on the performance of healthy children. In contrast, on the high-load task, noise actually decreased recall performance of healthy children, and had no effect on ADHD children.

This result provides some support for the idea that chronic understimulation is a causal symptom of ADHD, and that it can be at least partially remedied in terms of performance on simple recall tasks with the administration of loud white noise. Critically, this effect is limited to low-load memory tasks; if the effect were due merely to “drowning out distractions” one would expect the same benefit on the high-load task. Instead, there is no observed benefit there, suggesting that the mechanism may indeed involve stochastic resonance.

Intruigingly, this is to my knowledge the first demonstration that stochastic resonance from the perceptual system may have beneficial effects by carry-over into the more cognitive domains of encoding and recall. Stochastic resonance is more typically observed in sensory discrimination and detection experiments.

On the other hand, there’s plenty of reason for doubt here, too. Other studies have shown that background music is also beneficial in ADHD. The phenomenon observed here might therefore have less to do with stochastic resonance per se as providing some peripheral but continuous source of excitation to the chronically understimulated. It is therefore confusing that the authors chose a silent control, when a simple musical background might have ruled out this alternative explanation.

Comments

  1. #1 .nathan
    September 21, 2007

    As an adult who has been diagnosed with ADHD, I can attest that (for me anyway), if I work with music on, or a movie, or something else that I don’t really have to pay attention to I can stay on task a lot longer.

  2. #2 David Dufty
    September 23, 2007

    Nice observation at the end of your post: this data is interesting, but there are multiple plausible explanations that weren’t addressed or controlled for.
    I get frustrated by good science that is then used to over-reach and draw conclusions that just aren’t in the data.

  3. #3 Amy
    October 1, 2007

    This study is really interesting – as an adult with ADD, I’ve definitely noticed the same thing: I work far, far better when there is a lot of noise in the background than when there isn’t. And it’s best of all when the noise itself isn’t too patterned – in other words, things like coffee shops or train stations are best, because the noise is fairly random (and loud); listening to soft classical music doesn’t help much, although it’s better than silence. I know, anecdote != data, but it’s nice to see a study that so perfectly parallels what I’ve maintained to my friends for years. :)

    Re: David Dufty’s comment, I share your frustration about overreaching conclusions, but I’m a little less bothered by it because a lot of times I’ve noticed that papers will suggest those conclusions and it seems like overreaching from just that one paper… but most of the time the paper is embedded in an entire strand of research, with many papers on the same topic, each addressing some of the confounds. And unless you know of the entire ouvre of work — including the planned upcoming experiments — it can look like overreaching, but it isn’t necessarily when taken in context. I’m not very familiar with this literature so I don’t know if my point applies here, but I think it’s somewhat generally true.

  4. #4 Nikki
    October 15, 2007

    I have recently been diagnosed with ADHD (inattentive). I find that I am greatly comforted when there is “white noise” in the background. In fact, I sleep with my fan on with the purpose of using the “white noise” to drown out the sound of my husband’s breathing/soft snoring.
    Also, I am in college and I have a hard time with the sound of other students chewing gum, rattling bags, or flipping papers in the classroom. It is not only distracting to me, it makes me feel *angry* and *disgusted* inside. I can’t control the feeling – and once I am out of the situation, I feel incredibly relieved, but guilty and confused by my reaction. I never actually *say* anything mean, but I often give glaring looks to the person causing the offending noise. I avoid theaters because of popcorn and bag-rattling, and sometimes, dinner with my family is unbearable- so, I hurry my eating or leave to avoid the *noises* and to avoid acting out.
    Sometimes, the *noises* are so unbearable that it makes me want to cry! In fact, once in a theater, I did cry (not noticeably) because I was so distressed and I could not escape – and of course, I could not act out and look like a freak.
    I have been plagued by this problem my entire life, and I am mostly able to cover it up… It does, however, affect my relationships from time to time when I am not able to hide my reaction. I try to explain, but no one understands my hyper-sensitivity and abnormal irritation, of course. Some have accused me of having an eating disorder or of being “psycho” (a word my ex-husband used when I would ask him to stop smacking or chew with his mouth shut).
    My doctor discovered the ADHD problem when I asked to speak with a couselor after my mother passed away (I was experiencing extreme anxiety over losing her). He set me up with a therapist, who diagnosed me with ADHD. I did not even mention the noise problems with my therapist until another session, where he said that this was definitely a symptom of ADHD. I don’t think that he understands the depth of the problem, though. In fact, I’ve been hiding it for so long, that I don’t think that “I” even knew how much of my life is/has been affected.
    The therapist prescribed concerta and lexapro – at first, the noise irritation seemed so much better, but when I started this semester of college, I feel as though the problem is actually enhanced. However, other areas have improved drastically – such as my ability to organize my ideas and communicate them, better motivation, and an overall ability to listen and absorb what is being said.
    Something else to note is that my reaction to the *noises* are completely uncharacteristic of my normal behavior. I am a very soft-spoken, soft-hearted, easy going person… but sometimes the *noises* cause me to glare, sigh audibly, and withdraw. If the offender happened to be a family member or someone that I am close to, there have been times when I’ve said very mean things about their eating habits. Often I will try to drown out the offending noise by being louder (like when someone is eating chips, I make sure that I am eating some, too – this helps because my own eating noise does not bother me and it drowns out the irritant noise).
    Reading your research really peeked my interest. In my case, “white noise” is indeed helpful. Music can sometimes distract my concentration, but the sound of a fan or airconditioner is comforting when I am in a situation from which I can not escape.
    Another note: These *noise* issues that I experience are so close to symptoms of Autism – it’s not some mild version or subcategory, is it?

  5. Chris,
    Excellent post, well written up, and repeatedly documented/reported in my daily practice with individuals who have ADD. So often family disputes arise with the “you can’t concentrate with all that noise” comments – and when we negotiate exactly what that noise can be for the person and the family, all goes much better.

    Regarding David Dufty: In studies with individuals who have ADD there are many variables often overlooked that can’t be easily controlled. ADD by definition can have many expressions, and I have personally seen ADD symptoms on the surface with at least 13 different brain patterns on SPECT.

    It is my impression from this article that the author is not attempting to speak categorically – asserting that “noise is good for all ADD” – but is noting that some subsets appear to improve in certain contexts with specific types of “noise” – a perfectly provable point with my everyday large office n numbers, large numbers with years of follow up.

    I will post on this post soon, and appreciate your heads up!
    Thanks
    Chuck

  6. #6 Nick
    March 27, 2009

    In case Nikki is still out there 18 months after she wrote the above about her ADHD and noises – I would love to hear from you (nic2mitchell@yahoo.co.uk). You and I have uncannily similar experiences and I have never found anyone else with this problem. I too have been recently diagnosed with ADHD (inattentive).

  7. #7 Rooney
    October 25, 2009

    My son has ADHD, as do I. However, he needs to have noise all the time when he is working. He is always listening to music when he is doing his homework. I can’t understand it, because I, on the other hand, am like Nikki. I just can’t handle any extraneous noise. I have to have absolute silence to read or do any mental work. I get incredibly irritated with anyone making noise of any kind when I am TRYING to concentrate.

    I don’t get the difference between my son and I. Do we have different types of ADHD, or is it just individual differences?

  8. #8 dinleme cihazları
    December 25, 2009

    It is my impression from this article that the author is not attempting to speak categorically – asserting that “noise is good for all ADD” – but is noting that some subsets appear to improve in certain contexts with specific types of “noise” – a perfectly provable point with my everyday large office n numbers, large numbers with years of follow up.

  9. It is my impression from this article that the author is not attempting to speak categorically – asserting that “noise is good for all ADD” – but is noting that some subsets appear to improve in certain contexts with specific types of “noise” – a perfectly provable point with my everyday large office n numbers, large numbers with years of follow up.

  10. #10 ses kayıt
    December 7, 2010

    I am close to, there have been times when I’ve said very mean things about their eating habits. Often I will try to drown out the offending noise by being louder. Music can sometimes distract my concentration, but the sound of a fan or airconditioner is comforting when I am in a situation from which I can not escape.

  11. #11 Jens-W. Schicke
    December 12, 2010

    The paragraph under the image got it wrong (or is written incredibly misleading). The top row is not showing the signal but what remains after they put the (sine: left, square: right) signal through their neural model.

    What they claim is not that adding noise will help you better see the signal, but when adding noise, it will help you better see the signal after a neuron has processed it.

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