12/07/2012

A Tale of 2 Digit Spans: A possible simple way to distinguish between ADHD & auditory processing problems

Your child is busy playing and you tell him to clean up his room.  Maybe you can't get him to look up at you and nod or say something to acknowledge your speaking to him.  Or maybe he does this and you leave the room, only to come back ten minutes later and find him in the exact same spot.  You've checked his hearing and it tested normal.  He also seems contrite rather than aggressive about it, so he probably isn't ignoring you just to annoy you.  Your teacher thinks it might be ADHD.  A news article you read suggests your child might have an auditory processing disorder instead--his brain can't process what you say very well, even though his ears work fine.  Who is right, and why won't your child just do what you tell him the first time?

If your child has auditory processing problems, then they could be paying perfect attention and still have difficulty understanding what you said.  They might have difficulty making out the words, and miss or misinterpret some of them.  They might have poor memory for what they hear (but not for anything else), so that if you give them long instructions, they won't remember the beginning by the time you get to the end.

If your child has ADHD, there are two possible ways your child could be failing to process your instructions: attention and working memory.  First of all, if your child was highly focused on doing something before you spoke to him, you may not have gotten his attention in the first place.  Or, if your child is highly distractible, they may have switched to thinking about something else or looking out the window halfway through your sentence.  Working memory is the amount of information we can hold in mind at one time while working with it, and it's a major weakness in ADHD.  If you give a child with poor working memory multi-step instructions, she will have forgotten step 1 by the time you finish explaining step 3 (or might miss step 3 because she was too busy repeating step 1 to herself so she won't forget it).  If your child is always rushing off to write or draw her ideas before she forgets them, she might have poor working memory.

You'll notice that poor working memory works very similarly to having poor memory for what you hear in auditory processing disorder.  However, there is one key difference: if you have poor working memory, this will be true not only for what you hear but for what you see, read, and think.  If your auditory memories simply fade quickly, it only affects what you hear--not what you see, read, or think.

I recently stumbled on a possible way to distinguish these two problems just by using two different versions of a common standardized working memory test: the "Digit Span" task.  

The Digit Span task involves playing a recording of alternating words and single-digit numbers (e.g. "cat, 9, house, 2"), which starts out with two items and gets increasingly long.  The listener must rearrange the items according to a specific rule and say the rearranged list to the examiner.  The task ends when the listener gets a certain number of lists wrong.  The average person has a digit span of about 7, plus or minus 2 (a famous number in cognitive psychology).

There are different versions of the Digit Span task, and they have different rules.  One version of the task, which I have been tested on myself and have also administered to children, requires you to keep track of the order in which you heard the items.  You must first repeat back the words in the order you heard them, then repeat the numbers in the order you heard them (so "cat, 9, house, 2" becomes "cat, house, 9, 2").  Another version of the task, which I encountered while participating in a study comparing prospective memory in NT and ADHD adults, works quite differently.  You must put the items in alphabetical and/or numeric order.  So "cat, 9, house, 2" becomes "cat, house, 2, 9."  

I found the first version incredibly difficult.  By the time I got to lists with 5 items, I was struggling.  If I didn't quite hear a word ("was that dog or duck?") I would have to try to reconstruct the word while taking in the rest of the list.  I found it was quite easy to remember what all the items were once I heard them, but difficult to remember the order in which I heard them.

My experience with the second version was quite different.  I had no difficulty whatsoever putting the items in alphabetical and numerical order.  The examiner was looking at me with astonishment as I breezed through 7-item lists.  

In asking myself why one Digit Span task was so hard and the other so easy, I realized that the first version tapped more than just the ability to hold onto information while rearranging it.  It also required you to have good auditory processing, where the traces don't fade right away.  While I appear to have good working memory, I have poor auditory processing, and this got in the way of remembering what I heard in what order.  The information simply faded from mind before I could use it.

So how does this apply to distinguishing kids with poor working memory due to ADHD from kids with poor auditory memory due to Auditory Processing Disorder?  A person with ADHD would have difficulty simply remembering and rearranging all the items, whichever version of the task they get.  They don't have the working memory to do the task well, regardless.  A person with auditory processing problems would, like me, have more difficulty when instructed to remember the order in which they heard the items.

Of course, controlled studies need to be carried out to demonstrate that these tasks really do distinguish diagnosed ADHD kids from diagnosed APD kids.  My experience could stem from sheer random chance or, more likely, idiosyncratic variables about myself and the testing situations.

However, if the different Digit Span tasks really do differ in the way I suggest, it also matters to researchers, whether they want to disentangle working memory from auditory processing problems in disabled populations or they just want to understand how working memory develops in typical people.  If all versions of the Digit Span task do not necessarily measure exactly the same thing, choose the one that assesses what you really want to measure.