\section{Results}\label{results}

The overall workload scores for all the five subjects were calculated and averaged to get mean overall workload scores for each task on a scale of 0 to 100.


\begin{figure}[t]
\centering
\includegraphics[width=0.80\textwidth]{oaWork}
\caption[Obstacle Avoidance Workload]{Overall workload scores for Obstacle Avoidance behaviour testing. \textquoteleft{Manual}' and \textquoteleft{Shared}' correspond to manual and shared mode, respectively. \textquoteleft{Secondary}' refers to presence of secondary task. Mean workload values are indicated in red. Boxes represent the inter-quartile range, line within each box - the median, and whiskers - the range of data}
\label{fig:oaWork}
\end{figure}

The overall workload ratings for tests conducted to assess Obstacle Avoidance behaviour is shown in \hyperref[fig:oaWork]{Figure 5.4}. The variation in workload ratings between the volunteers is clearly visible. It is particularly high in the case of shared control (without secondary task), with workload scores ranging between 23 and 87.67 (standard deviation - 25.8). The reasoning for this observation could be that the volunteers did not show the same response or have the same level of acceptance for the shared control assistive behaviours offered by the wheelchair.

\begin{figure}[t]
\centering
\includegraphics[width=0.66\textwidth]{oaM}\\
\includegraphics[width=0.66\textwidth]{oaS}
\caption[Obstacle Avoidance Sources of Workload]{Sources of load for manual and shared control without secondary tasks. Each subscale is rated from 0 to 100 and given a weight from 0 to 5. Hence the maximum adjusted rating (rating x weight) for a subscale is 500. MD refers to Mental Demand, PD - Physical Demand, TD - Temporal Demand, P - Performance, E- Effort, F- Frustration}
\label{fig:oaRes}
\end{figure}


It can be observed that the workload scores for shared control are higher than that for manual mode, with and without the secondary task. This can be attributed to the restrictions imposed by the collision avoidance behaviour, particularly in narrow spaces. Volunteers had to spend more time to re-position themselves in order to proceed in the required direction. This increased their frustration and sense of 
performance. These findings are represented in the graphs in \hyperref[fig:oaRes]{Figure 5.5} showing the sources of workload for manual and shared control modes. Another observation is the perception of workload in the presence of the secondary task.  While the workload of the secondary task alone is low, when combined with the manual mode driving task, the resultant workload is high. The change in workload in the case of shared control is not as much as in manual mode.

The results for testing the Wall Following behaviour is provided in \hyperref[fig:wfWork]{Figure 5.6}. Variations between different volunteers are observed in this case as well. Workload scores for manual mode with secondary task shows highest variability (standard deviation - 26.1). But the mean workload is highest for this task. This can be explained by the increased user intervention required to correct for wheelchair drift, in addition to performing the secondary task. User intervention was however required in shared control mode near the corners since the wheelchair did not always negotiate corners properly.

\begin{figure}[t]
\centering
\includegraphics[width=0.80\textwidth]{wfWork}
\caption[Wall Following Workload]{Overall workload scores for Wall Following behaviour testing. \textquoteleft{Manual}' and \textquoteleft{Shared}' correspond to manual and shared mode, respectively. \textquoteleft{Secondary}' refers to presence of secondary task. Mean workload values are indicated in red. Boxes represent the inter-quartile range, line within each box - the median, and whiskers - the range of data}
\label{fig:wfWork}
\end{figure}

The effectiveness of the shared control approach is shown by the lower overall workload scores, both with and without secondary task. This can be attributed to the predictability of the shared control behaviour in this mode as opposed to the obstacle avoidance mode. Three of the volunteers found shared control beneficial in this task, one perceived no difference and one found manual control easier. The latter volunteer seemed unable to gauge the path followed by the wheelchair and frequently tried correcting its position.

