# Human-Robot Collaboration: An Augmented Reality Toolkit for Bi-Directional Interaction
## 6 Experiments
### Analysis of the Results
#### 6.3.1 NASA TLX Results  
In Figure 15 the main results of the NASA TLX survey are reported. Statistically significant differences have been found in the mental and physical demands between the two interfaces. The kinesthetic system appears to require less mental effort (\(Mean=28.56\%\)_Standard Deviation_\(=17.44\%\)) than the use of the AR system (\(M=36.22\%\), \(SD=22.19\%\)), \(t(44)=2.8350\), \(p=0.0069\), \(d=0.3690\), as depicted in Figure 15b.  
The mental workload required by the AR platform is strictly dependent on the interaction skills with holograms, as well as related to the ability to remember the specific sequence of buttons; on the other hand, the kinesthetic teaching interface provided by the cobot is extremely intuitive and user-friendly. It is not hard to imagine that an XR novice would tackle challenges when interacting with the virtual reality features. An appropriate evaluation should consider the different background of the participants in relation to XR devices. To this aim, Figure 16 shows the comparison between upper-intermediate users' assessments on mental workload (14 among 45 participants, depicted in grey) compared to those of participants with lower levels of AR expertise (31 among 45, in blue). The difference between the two samples in the case of the kinesthetic interface is almost negligible, while, in the case of the AR platform, a great discrepancy is experienced: the mental workload points out a sensible increment for the non-expert users, whilst for the expert users it is comparable with the other interface. Thus, one could argue that the mental load requested by the AR platform can be easily reduced with a more intensive training phase on the HoloLens device, as it is rather due to the participants' inexperience than to the complexity of the proposed application.  
On the other hand, as reported in Figure 15c, the kinesthetic interface necessitates more physical demands (\(M=23.78\%\), \(SD=20.84\%\)) than the AR interface (\(M=13.89\%\), \(SD=13.94\%\)), \(t(44)=3.7025\), \(p=0.0006\), \(d=0.5358\), as evidenced by a larger effect size.  
It is an expected result since the kinesthetic teaching method requires users to physically move the robot to each way-point of the desired path, whereas the AR-robotic interface does not need physical interaction.  
There are no other noteworthy variances in the other dimensions. Nonetheless, the adoption of the AR platform results in decreased temporal demand and effort while yielding better performance levels (85.89% without the HoloLens platform, 88.44% with the HoloLens). Although it does not represent a statistically significant difference, the overall NASA TLX, depicted in Figure 15a is slightly decreased with the AR interface (\(-6.13\%\)).  
Figure 16: Mental demand for kinesthetic and AR interfaces, with comparison between different levels of AR expertise; error bars represent 95% CIs.  
Figure 15: NASA TLX, mental demand and physical demand for kinesthetic and AR interfaces; error bars represent 95% confidence intervals (CIs).