Posted by: wolf | March 4, 2008

Attention deficits: The influence of rewarding performance

Do you often feel restless, do you think you are more easily distracted than others, and often react impulsively? Attention Deficit Hyperactivity Disorder (ADHD) is one of the better-known psychological or “neurobehavioral” disorders — a google search for “ADHD” gave more than 32 million hits.

I will not be going into a discussion of treatments for children with ADHD — you will surely find enough of that on the web. This will be about a specific study on adults with attentional deficits, whose problems have been paid more and more attention (if you pardon the pun) in recent years. According to the NIMH, about 1-3.5% of adults are suffering from ADHD, with their problems usually continuing from childhood. And there isn’t a sharp distinction between people with and people without the disorder, it’s rather a continuum with some people exhibiting more problems than others; the disorder will be diagnosed when the problems are excessive, long-term, and pervasive.

Children and later adults with ADHD often are at risk for long-term difficulties in academic and occupational achievement, and sometimes even for more serious problems, so a major question is how to treat the disorder. As you may well know, the most recommended treatment for children is a combined strategy of medication and behavior treatment. In adulthood, hyperactivity problems often decrease, but attentional problems remain, and thus the problem will not always be obvious to others and neither to the person concerned. From a behavior therapy point of view, Lee and Zentall review theory on what variables mediate the effect of ADHD on general performance in adults, variables that may be influenced in order to decrease the detrimental effects of the disorder. A motivational explanation is that ADHD makes people more sensitive towards rewards: they need to be rewarded more often and are more easily frustrated when there is no reward for a specific task.

In Lee and Zentall’s experimental study, 15 students with attentional deficits and 21 students in the control group had to press a button as fast as possible whenever they heard the letter “A” in a series of 12 letters altogether, a task of sustained attention. In a continuous reward condition they were verbally “rewarded” (“right”) each time they responded correctly, in a partial reward condition with rewards delivered on 30% of correct trials; this makes 2×2=4 groups, A(ttentional deficits)-C(ontinuous), A-P(artial), C(ontrol)-C, and C-P. Each participant went through 50 “trials”, where each trial was a series of 11-20 letters with two targets (“A”). For the results, Lee and Zentall further summarized 10 consecutive “trials” into five blocks; during the last two blocks (i.e. 20 “trials”), no rewards were given for any of the groups in order to measure extinction/performance decreases. The dependent variable was reaction time, and additionally it was recorded how much force participants exerted when pressing the button as a measure of their frustration.

As expected, participants with attentional deficits (the A-C and A-P groups) performed (almost) as good as normal participants during the reward phases in terms of reaction time, but in the extinction phase they performed significantly worse (see figure 1).

Reaction times for the Lee and Zentall (2006) experiment for adults with attentional deficits

But there is an interesting side effect: even if the performance of participants with attentional deficits was almost as good as that of the control group on average (mean reaction time for a block with 10 trials), within a block their performance was much more variable (figure 2), and even more so during the extinction blocks.

Standard deviation of reaction times for five blocks in the Lee and Zentall (2006) experiment for adults with attentional deficits

Unexpectedly (for the authors) there weren’t any real differences concerning the pressure exerted.

Taken together, I think this is in some respects a nice little study: It shows that attentional deficits really do manifest even in adult subjects which can be regarded as nicely adapted socio-psychologically — after all, participants all were college student. And what is more important, it shows that there exist simple measures to cope with attentional problems: One needs to be rewarded continuously and on a shorter time scale.

On the other hand, I have to do some methodological nit-picking: What the researchers really had were absolutely nice time series data (i.e. reaction times for each target), so why did they have to dump them together first into “trials” and then, even worse, into blocks? Both of the main results, e.g. similar performance on average and greater variability could have been demonstrated even better had they not dumped the single reaction times together. But of course, time series analyis is generally neglected in psychology.

Lee, D.L., Zentall, S.S. (2006). The effects of continuous and partial reward on the vigilance task performance of adults with attentional deficits: A pilot investigation. Journal of Behavior Therapy and Experimental Psychiatry, 37(2), 94-112. DOI: 10.1016/j.jbtep.2004.12.001


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