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Study suggests the real deficit underlying Attention Deficit Disorders is not Attention, but Working Memory


Many par­ents have observed that their child with ADHD stays atten­tive and engaged dur­ing ‘high inter­est’ activ­i­ties, e.g., while play­ing video games, but has con­sid­er­able prob­lems stay­ing focused on less inher­ent­ly engag­ing tasks, e.g., doing school­work. This dis­crep­an­cy in atten­tion dur­ing pre­ferred and non-pre­ferred activ­i­ties has led some to spec­u­late that chil­dren with ADHD don’t have under­ly­ing neu­rocog­ni­tive deficits that explain their atten­tion dif­fi­cul­ties, but that they sim­ply don’t try as hard when they are not inter­est­ed or moti­vat­ed.

Sur­pris­ing­ly, there has been lit­tle research to doc­u­ment this obser­va­tion. And, if dif­fer­ences in atten­tion for chil­dren with ADHD dur­ing pre­ferred and non-pre­ferred activ­i­ties were found, would this reflect deficits in impor­tant neu­rocog­ni­tive process­es rather than their just not try­ing as hard when they are not inter­est­ed?

The New Study

Those ques­tions were addressed in the study titled Inat­ten­tive behav­ior in boys with ADHD dur­ing class­room instruc­tion: the medi­at­ing role of work­ing mem­o­ry process­es, pub­lished recent­ly in the Jour­nal of Abnor­mal Child Psy­chol­o­gy.

Par­tic­i­pants were 62 8–12 year-old boys, includ­ing 32 with a con­firmed diag­no­sis of ADHD. Each par­tic­i­pant watched two 10-minute video clips: one was an instruc­tion­al math video that pre­sent­ed age-appro­pri­ate math infor­ma­tion the way a teacher might and the oth­er was an action-packed sequence from a Star Wars movies.

Boys were video­taped while watch­ing each clip so the per­cent of time they attend­ed to each video could lat­er be deter­mined. This mea­sure of visu­al atten­tion was made by trained observers who did not know whether the boys were in the ADHD or com­par­i­son group.

Work­ing mem­o­ry — Work­ing mem­o­ry (WM) is the cog­ni­tive sys­tem respon­si­ble for the tem­po­rary stor­age and manip­u­la­tion of infor­ma­tion; WM plays an impor­tant role in both learn­ing and focus­ing atten­tion. Con­sid­er­able research has doc­u­ment­ed that many indi­vid­u­als with ADHD have WM deficits and that this con­tributes to dif­fi­cul­ties asso­ci­at­ed with the dis­or­der. In fact, some researchers — includ­ing the authors of this study — hypoth­e­size that the core symp­toms of ADHD are sec­ondary to WM deficits. They argue that it is when a child’s WM capac­i­ty is exceed­ed that prob­lems with atten­tion and hyper­ac­tiv­i­ty become evi­dent.

A sim­ple exam­ple illus­trates the impor­tance of WM for par­tic­u­lar aca­d­e­m­ic tasks. Try adding 3 and 9 in your head. That was prob­a­bly easy. Now, try­ing adding 33 and 99. That was prob­a­bly more dif­fi­cult. Final­ly, try adding 333 and 999. This is quite chal­leng­ing for most adults even though each cal­cu­la­tion required is easy. The chal­lenge occurs because you need to store infor­ma­tion — the sum of 3+9 in the one’s col­umn and then in the ten’s col­umn — as you process the remain­ing part of the prob­lem, i.e., 3+9 in the hun­dred’s col­umn. Most peo­ple find that this strains their WM capac­i­ty; and, if your WM capac­i­ty is exceed­ed, you could not com­plete the prob­lem. It is not hard to imag­ine how chil­dren whose WM skills are sub­stan­tial­ly below their peers would strug­gle in the class­room and how this could be man­i­fest as inat­ten­tive behav­ior.

In addi­tion to hav­ing boys watch the videos, the researchers care­ful­ly mea­sured their WM skills. This enabled the researchers to test whether any dif­fer­ences in atten­tion they found between boys with and with­out ADHD dur­ing the 2 videos was relat­ed to dif­fer­ences in their WM. They pre­dict­ed that:

1. Atten­tion dur­ing the Star Wars video would not dif­fer for boys with and with­out ADHD.

2. Boys with ADHD would dis­play poor­er atten­tion dur­ing the Math Instruc­tion video. This is because the WM demands to fol­low along what is pre­sent­ed in the WM are sig­nif­i­cant­ly greater than what is required in the Star Wars video

3. The drop in atten­tion dur­ing the Math Instruc­tion video for boys with ADHD would be explained by their poor­er WM skills.

Thus, the researchers sought to doc­u­ment par­ents’ long-stand­ing obser­va­tion that atten­tion prob­lems in their child with ADHD are most evi­dent dur­ing less inter­est­ing tasks, and, that inat­ten­tion dur­ing such tasks reflects deficits in spe­cif­ic neu­rocog­ni­tive process­es, i.e., WM capac­i­ty, rather than a moti­va­tion­al deficit, e.g., lazi­ness.

The Results

Results from this study were con­sis­tent with pri­or research and sup­port­ed the authors’ hypothe­ses. Specif­i­cal­ly, they found that:

1. As doc­u­ment­ed in pri­or stud­ies, boys with ADHD had specif­i­cal­ly low­er WM scores than com­par­i­son boys.

2. Dur­ing the Star Wars video, there was no dif­fer­ence in the per­cent of time that boys in each group were pay­ing atten­tion.

3. Although atten­tion in both groups of boys dropped dur­ing the Math Instruc­tion video, it dropped by sig­nif­i­cant­ly more in boys with ADHD, i.e., by 16% com­pared to only 7%. They note that based on guide­lines for rec­om­mend­ed dai­ly math instruc­tion­al time for 3rd-5th graders, a 16% decre­ment in atten­tion dur­ing dai­ly math instruc­tion is equal to miss­ing rough­ly 29 math lessons across the school year. 4. Over half of the atten­tion dif­fer­ences between boys with and with­out ADHD dur­ing the Math Instruc­tion videos was explained by WM dif­fer­ences between the groups. In oth­er words, when WM dif­fer­ences between the groups was account­ed for, dif­fer­ences in atten­tion dur­ing the math video declined by more than half. Thus, there was evi­dence that deficits in this impor­tant neu­rocog­ni­tive func­tion is an impor­tant con­trib­u­tor to the atten­tion deficits that youth with ADHD often dis­play dur­ing class­room instruc­tion.

Summary and implications

Results from this study val­i­date the obser­va­tion made by many par­ents that atten­tion prob­lems for chil­dren with ADHD are far more like­ly to be evi­dent in some con­texts than oth­ers, i.e., dur­ing non-pre­ferred but not dur­ing pre­ferred tasks. As demon­strat­ed in this study, the gap in atten­tion between boys with and with­out ADHD clear­ly emerges dur­ing instruc­tion­al activ­i­ties that require sus­tained atten­tion. This gap was suf­fi­cient­ly large to help explain why chil­dren with ADHD would mas­ter few­er math skills across an aca­d­e­m­ic year.

Study find­ings also sup­port the impor­tant role of WM in explain­ing why atten­tion deficits emerge dur­ing instruc­tion­al tasks. The math video required greater WM capac­i­ty to fol­low along, and the authors demon­strat­ed over half the drop in atten­tion for the boys with ADHD dur­ing the math video was account­ed for by their poor­er WM. They argue that this indi­cates that youth with ADHD show atten­tion prob­lems in some con­texts but not oth­ers because of a spe­cif­ic neu­rocog­ni­tive deficit, and not because they are less moti­vat­ed to engage in tasks that don’t inter­est them.

What are the inter­ven­tion impli­ca­tions of these find­ings? First, one could design class­room and instruc­tion tech­niques that reduce the WM demands on chil­dren with low WM abil­i­ty. While this makes good sense, pos­i­tive effects of com­pen­sato­ry class­room inter­ven­tions remain to be clear­ly demon­strat­ed. Sec­ond, one could work to train WM skills direct­ly. There has been sub­stan­tial research done on work­ing mem­o­ry (WM) train­ing and pos­i­tive results in a num­ber of indi­vid­ual stud­ies have been report­ed. How­ev­er, com­pelling evi­dence that WM train­ing yields clin­i­cal­ly mean­ing­ful improve­ment in out­comes relat­ed to class­room instruc­tion and aca­d­e­m­ic achieve­ment is not yet avail­able. Thus, this is an area where ongo­ing efforts to devel­op effec­tive inter­ven­tions is need­ed.

There are lim­i­ta­tions of this study to note. First, the sam­ple was exclu­sive­ly male and sub­se­quent work is need­ed to con­firm whether a sim­i­lar pat­terns of results is obtained with females. Sec­ond, the authors acknowl­edge that in addi­tion to dif­fer­ing in WM demands, the 2 videos dif­fered on oth­er dimen­sions that could impact chil­dren’s atten­tion, e.g., the rapid­i­ty in which scenes changes, the lev­el of visu­al imagery and sounds, etc. They note that sub­se­quent work should vary the lev­el of WM demands with­in videos that are equal­ly engag­ing visu­al­ly. This would help to more clear­ly deter­mine whether WM demands are the key fac­tor relat­ed to the emer­gence of inat­ten­tive behav­ior in some con­texts but not oth­ers.

– Dr. David Rabin­er is a child clin­i­cal psy­chol­o­gist and Direc­tor of Under­grad­u­ate Stud­ies in the Depart­ment of Psy­chol­ogy and Neu­ro­science at Duke Uni­ver­sity. He pub­lishes the Atten­tion Research Update, an online newslet­ter that helps par­ents, pro­fes­sion­als, and edu­ca­tors keep up with the lat­est research on ADHD, and helped pre­pare the self-paced, online course How to Nav­i­gate Con­ven­tion­al and Com­ple­men­tary ADHD Treat­ments for Healthy Brain Devel­op­ment.

The Study in Context

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