Game Development Reference
In-Depth Information
of no use to have metrological characteristics that are better than the psychophysical
characteristics. If they are inferior, which sadly is often the case, we can determine the
quantity of the relative “sensorimotor'' deficit for each stimulated sense and motor
response. For example, for any visual interface, the display should be such that the
two adjacent pixels are less than 1 minute of angle away with respect to the user's
viewpoint, as his visual acuity is minimum 1 minute of angle. But currently we often
use higher values, especially in the head-mounted displays. In the case of sensorimotor
deficit, we must examine whether it is compatible with the desired cognitive I 2 . Accu-
racy, sensitivity, scope of use, measurement frequency and response time are the most
important metrological characteristics for an interface.
Assessment tests should be carried out at the level of sensorimotor I 2 . The designer
should not content himself with verifying that the characteristics of the interface are
sufficient with respect to the application. The sensorimotor I 2 and the cognitive I 2
should not be assessed at the same time . We cannot explain all types of tests in this
general chapter, but we will discuss them for each type of interface in the correspond-
ing chapters. However, we will give one example just to draw our reader's attention
towards it. While examining a top-of-the-range head-mounted display, we assessed the
fields of view - horizontal and vertical - of both eyes. We measured effective values
by moving the references (lines, cross marks, etc.) in the field of vision of a number of
observers. The values were lower than the values mentioned in the product leaflet. In
addition, it was not possible to reach the maximum horizontal field of vision and the
maximum overlap of the field of vision of both the eyes (the stereoscopic field) at the
same time, which was never mentioned in the leaflet. In other words, all characteristics
must be verified because even if the characteristics mentioned in the leaflets are correct,
there is no guarantee that the interface will be operated in the best conditions after the
installation. It can depend on the computer, software, data and the user.
In case of cognitive I 2 , it is difficult to quantify the assessment. When an IBS is
chosen offhand, the validation tests should confirm the choice made. The schema is
more effective when the time required to learn using the BI is less. To assess the perfor-
mance of a natural behavioural interface in practical terms, we suggest carrying out
the standard tests of ergonomics. The time required to learn is a good indicator. If the
interface uses an Imported Behavioural Schema that is less altered in the virtual envi-
ronment, the users will interact more comfortably after a very short self-learning time.
The learning time to be considered as short will vary from application to application.
As will be explained in the paragraphs below, if a consumer takes 20 minutes to finish
shopping in a virtual shop, the total time for learning the I 2 should not be more than
2 to 3 minutes. If the SNCF driving crew has to be trained in a single day to perform
some tasks on a railway infrastructure, they should not take more than 15 minutes to
learn the I 2 . During this learning time, the subject will understand his own use of the
system and will organise his virtual world. From the psychological point of view, we
are in the phase of design by use . The assessment is more difficult at the cognitive level
because it is necessary to consider the fusion of sensory stimuli giving coherence to the
virtual environment and the action taken by the subject. It is not possible to analyse
sense by sense as we do at the sensorimotor level. Assessing the interfacing becomes
tricky when it is necessary to consider the multimodality.
For functional I 2 , we can give only one general rule for assessment. The function
of the VR device must be compared to a similar function in a real world if it is possible
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