As discussed in Section 7.3, foreground occlusions may be useful additions to HMD's both to increase presence at a constant FOV and to reduce binocular rivalry effects. This is an option which HMD manufacturers might want to consider more seriously. There are ergonomic and safety issues associated with using a foreground occlusion which would have to be evaluated for each HMD design.
The research of Appendix C failed to find a performance effect for foreground occlusions in terms of a simple spatial orientation task. However, a foreground occlusion effect might be measurable with a nulling measure. The relative effect on presence of a foreground occlusion and wider FOV would be an interesting topic of study. The results of Experiment AIE1 suggest that for about a third of participants, the foreground occlusion effect had as strong or stonger an effect on presence as wider FOV, at least using a reported presence measure over a range of fairly narrow FOV's.