\section{Secondary Task}\label{secondaryTask}

Secondary tasks, as previously mentioned in Section 2.5, provide a means of assessing the effectiveness of shared control. The wheelchair driver is deliberately distracted by an activity that requires him or her to divert his focus elsewhere while driving the wheelchair. This method of testing is particularly useful when the subjects are able-bodied volunteers, since they are capable of efficiently manoeuvring the wheelchair without shared control. Hence the benefits of shared control, if any, would be masked by their skills. 


\begin{figure}[t]
\centering
\subfloat[Red slide]{\label{fig:red}\includegraphics[width=0.3\textwidth]{red}}
\vspace{2mm}
\subfloat[White slide]{\label{fig:white}\includegraphics[width=0.3\textwidth]{white}}
\vspace{2mm}
\subfloat[Math slide]{\label{fig:math}\includegraphics[width=0.3\textwidth]{math}}
\caption[Secondary task slides]{Screenshots of three consecutive slides of the slideshow used as the secondary task}
\label{fig:secTask}
\end{figure}

In this experiment, a secondary task was designed that required the volunteer to respond to  visual stimuli displayed on a 14 inch laptop monitor positioned in front of or beside them, as per their convenience, without obstructing the view of the simulator screen. A slideshow was displayed on the monitor that consisted of three types of slides occurring in random order every two seconds. Snapshots of three successive slides from the slideshow are shown in \hyperref[fig:secTask]{Figure 5.1}. The red slide required the volunteer to turn his or her head to the right so as to look away from the screen and then turn back again quickly. The white slide did not require any response from the volunteer. The third type of slide had mental arithmetic questions involving single digit addition or multiplication problems. Volunteers were asked to orally provide the solution for the problems without looking away from the simulator screen. In order to reduce any frustration caused by being unable to answer the questions correctly within the stipulated time, they were allowed to simply read out the question if they could not provide the answer immediately.
