\section{Experimental Procedure}\label{expProc}

The volunteers were briefed on the purpose of the study, i.e., to assess their wheelchair driving experience with manual mode and shared control assisting in Obstacle Avoidance and Wall Following. The keypad control (illustrated in Section 3.2) was explained to them and they were allowed to test the wheelchair for a few minutes in both manual and shared control modes to familiarise themselves with its control and the environment. They were also informed of the position of the sensors and the assistance provided by the shared control behavioural modes.  Clarifications were provided for use of the NASA-TLX scales if any questions were raised about the same. The secondary task was explained as well. Volunteers then carried out 4 tasks per assisting mode of Obstacle Avoidance and Wall Following as listed below, in addition to performing the secondary task separately. 

\begin{itemize}
\item Driving the wheelchair in manual mode 
\item Driving the wheelchair in shared control mode
\item Repeating each task above while simultaneously performing the secondary task
\end{itemize}

The volunteers were told their priorities while performing these tasks were to avoid collisions, to drive as fast as possible, to respond to the slides of the secondary task (where applicable) as quickly and correctly as possible, in that order, respectively. 

\textbf{\textit{Considerations:}} 

\begin{itemize}
\item {Although speed was not used as a parameter to measure their performance in this study, the volunteers were asked to drive as fast as possible to prevent them from being over cautious. It is to be noted that the maximum speed allowed in the manual mode was made equal to that in the shared control mode, in order to reduce the obvious frustration associated with not being fast enough in shared control mode compared to the manual mode.}

\item {Odd numbered volunteers started with Obstacle Avoidance tests and then went on to doing the Wall Following tests, and vice versa for even numbered volunteers. The order of performing the tasks using manual and shared control modes was also randomised. This was done to minimise any bias from learning effects (Carlson \& Demiris, 2010). Randomisation also helped to decrease context effects associated with the NASA-TLX scales (Hart, 2006). These occur when the perception of workload of a task is influenced by previous tasks and the ratings are affected drastically.}

\item {An exception to the randomisation was the order of the secondary task. It was expected that the workload in driving the wheelchair along with the secondary task would be higher than without it. Hence the feeling of workload would be greater if that particular task was being performed for the first time in a particular mode (manual or shared). It was hence reasoned that undue bias against the task would be avoided if the volunteer had already performed that task once in the respective mode before trying it with the secondary task.}

\end{itemize}

Details of the experiment specific to Obstacle Avoidance and Wall Following assisting behaviours are provided in the next two sections.

\input{chap5_5.3.1_oaTasks}

\input{chap5_5.3.2_wfTasks}


