The visual environment clearly starts with the lighting. In general, this should be kept at a level such that the talker feels comfortable and ``normal''. This should be mentioned because artificial recording environments are often illuminated at either very bright or rather dark levels.
Apart from this most basic property of the visual environment, additional devices are available to model the visual environment of the talker.
In most of today's practical implementations the visual displays of so-called Virtual Environment (VE) systems consist of two LCD monitors and some optics which are located close to each eye. The whole setup is assembled in a kind of ``helmet'' to be worn by the subject. The helmet also usually incorporates the head-tracker as well as the headphones.
From the acoustic room simulation point of view, wearing a helmet has a number of specific disadvantages and advantages, the first of which might be technically compensated for.
With regard to the paradigm described above, however, in which that a talker should not be aware of being subject to some kind of unconscious manipulation, it is obvious that a helmet of this type is cannot provide anybody with anything like a ``natural'' impression of the visual environment. Wearing a device as bulky and weighty as a helmet, no one can realistically be expected to behave in a natural way.
Finally, so far no system is known that would be technically capable of providing a realistic simulation of a natural environment, even if money is no object. In this respect, today's visual VE-systems are not considered to be superior to large scale frontal visualisation.
Frontal visualisation is a quite common technique in the speech recording area. Its application ranges from ordinary text prompting to more or less realistic face to face interaction between the talker and the recording operator.
When using frontal visualisations, especially those of rather large format, one should be aware of the fact that they cause acoustic reflections which in turn degrade the recording quality. Consequently, we would not recommend trying to project anybody into a ``virtual'' visual environment by seating him in front of a very large scale screen, if reflections might be a source of concern. The use of a screen should be restricted to pure prompting applications in which the monitor can be kept relatively small, and situated sufficiently far away from the microphone.