Attention Deficit Hyperactivity Disorder is estimated to affect 1 in 20 adults. While researchers agree on the main symptoms of ADHD, inattention, hyperactivity, and impulsivity, there is still considerable debate about the underlying deficit that causes these symptoms. Based on the work of Sagvolden et al.*, we are exploring the idea that the behavioral symptoms of ADHD can be explained by a timing disorder rather than an attention disorder.
Many studies in our lab and others have suggested that most humans have a similar sense of the duration of a "present moment" - a sense of how long "now" is. For most normal people, "now" is about 2-3 seconds long. If two events occur within this period, they are experienced as connected parts of the same whole. If the two events are separated by more than 2-3 seconds, however, they are experienced as distinct and unrelated.
If, as we predict, ADHD people have a shorter present moment, or sense of "now," then chained events that normal people perceive to be connected will be seen by ADHD people as separate and unrelated, which could give rise to an apparent lack of attention and overactivity. What a non-ADHD person sees as a short pause, the ADHD person sees as the end to one activity and an appropriate time to start another.
To explore this possibility of ADHD as time disorder, we‘ve been using studies designed to measure the present moment in both normal people and in people with ADHD. One experiment we‘ve had success with so far is a rhythm experiment, where participants synchronize their drum-tapping with a metronome, and then continue tapping at this pace without the metronome for 3 minutes.
We varied the target rate over 3 speeds: 60 bpm, 40 bpm, and 30 bpm. In previous studies, we‘ve found that normal participants can perform this task proficiently up until 40 bpm, or 1 tap every 1.5 seconds. At 30 bpm (1 tap every 2 seconds) or slower, participants lose their ability to feel the rhythm and drift around the beat. This supports the idea of a 2-second present moment. Each successive beat has to fall within less than 2 seconds of the last to allow rhythmic feel. The time disorder hypothesis predicts that ADHD people need the beats to arrive at even smaller intervals to feel rhythm, and this is what we find. While normal people lose their sense of the beat at 30 bpm, people with ADHD lose their sense of the beat at 40 bpm (see figure). This seems to suggest that people with ADHD experience the world on a faster time scale than other people do.
*Sagvolden, T., Johansen, E. B., Aase, H., & Russell, V. A. (2005). A dynamic developmental theory of attention-deficit/hyperactivity disorder (ADHD) predominantly hyperactive/impulsive and combined subtypes. Behavioral and Brain Sciences, 28, 397-419