Investigating the interference pattern of dual tasks using serial decomposition.

Background: Specific investigation of dual task-interference (DTI) may help researchers to develop the optimal training exercise for enhancing the performance of daily activities.

Objectives: To reveal the DTI by comparing the performances between personalized single tasks (cognitive or motor task) and dual task with serial decomposition in normal healthy adults.

Methods: After a preliminary period, healthy participants randomly (n = 46) performed three computerized experiments of cognitive (CT), motor (MT) and dual tasks (DT). In CT, participants were required to release button 1 (BT1) as rapidly as possible when the font color of a word and its meaning were congruent (Go), and in MT, they had to release BT1 and then tap button 2 (BT2) 10 times as rapidly as possible if the symbol "○" was presented (Go). The DT consisted of a combination of CT and MT elements. The reaction time (RT) of correct releases (RTCR) of BT1 in all tasks was measured, as well as the button shifting time between releasing BT1 and pressing BT2, and the finger tapping rate in MT and DT. To obtain the DTI values, we calculated the RTCR ratio in CT and MT and divided the outcome by the RTCR of DT.

Results: The ratio of RTCR in CT (% CT/DT, 78.6±13.0%) and MT (% MT/DT, 74.2±10.1%) were significantly lower than the ratio of RTCR in DT (% DT/DT, 100%). The button shifting time of MT was at 92.0±23.7% of baseline, and the finger tapping rate of MT was 106.1±19.1%, which was significantly higher than baseline.

Conclusions: The % DT/DT is significantly higher than both % CT/DT and % MT/DT, which suggests that the cognitive load depends on the type of cognitive task that is being performed. Additionally, the significant increase of % DT/DT compared to % CT/DT indicated that there is a cognitive load prior to a motor task. The increased button shifting time and decreased tapping rate in DT may indicate that a residual cognitive load and a concurrent motor load were present.