Noise

We received R’s report card this week. The report comments that R can be inconsistent when she is tired or unwell and that, as a result of this inconsistency, she is not ready to move on. I am disappointed and a bit frustrated. In mainstream schools, perfect performance on multiple tests is not required for a child to be allowed move on to the next level. This seems to be what is being asked of R.

In psychology, a common experimental procedure is to ask a subject to make a choice between two alternatives; only one alternative is correct. This procedure will be repeated on several (sometimes many hundreds of) occasions. If the subject makes the correct choice half of the time then it can be reasonably assumed that he is only guessing. If the subject makes the correct choice on three out of four occasions on average, then the chance that the correct answer has been arrived at purely by guessing is very small and the subject is assumed to have been able to do the task. R is usually tested by this procedure and she regularly gets every question right. Occasionally, her score drops below 100% but rarely below 75%. And very occasionally, when she really doesn’t want to do it, R gets every question wrong. (This is exactly equivalent to getting every question right.)

For psychologists, one of the ways to think about how humans are able to process information (or signals) is to consider the noise that is present within the system. For example, imagine the scene – R is unwell, and I am concerned with making sure she is comfortable, F is upstairs playing on his drum kit (what were we thinking?) and EB asks for a biscuit. I nod my assent. Two minutes later, I ask EB why she took a biscuit without asking. There is noise in the most literal sense here – provided by F’s drumming – but my focus on R and how she is feeling introduces further “noise” which also interferes with my ability to hear and to process EB’s question. Psychologists also think about the noise on a much more “microscopic” level – within cells of the nervous system itself.

Increasing the noise in a system whether at the macro or micro level, decreases the chance that any signal is going to be detected: if you have noise on a phone line it can be hard to understand what a caller is saying. If you have Rett syndrome, there is a whole lot of noise in the system. The level of the noise varies. For example, when R is well, she is much better able to communicate via her Eye Gaze computer than when she is unwell. It’s a complex procedure after all. We ask R a question, she must hear this question, process the information, formulate a response, and send the message to her eye muscles in order to move her eyes such that she fixes on the correct answer. When R is unwell, the increased noise at any of these stages could be enough to prevent her from completing the task. The experimental psychologist would be happy with her picking the correct answer three times out of four. Special schools seem to set the threshold far higher.

Post Script

Reading it back over, I am concerned that this post implies rather more criticism of R’s school than I had intended.  So to be clear: my criticism is of the system of education rather than her teachers.  Her teachers try very hard to find ways to explore R’s understanding but they are starting from scratch and I doubt very much whether teacher training includes classes on Signal Detection Theory.  Perhaps it should.

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