On-the-Move and in Your Car - Human-Computer Interaction and Innovation in Handheld, Mobile and Wearable Technologies - page 70

Figure 4. The occlusion method with participant wearing occlusion goggles, with shutters open (left)
and closed (right)

istics of torque feedback for steering on
curve negotiation (Toffin et al., 2003).

Following considerable research, the occlusion
method has recently been formalised as an inter-
national standard (ISO, 2005). In particular, guid-
ance is given on how many participants are re-
quired, how much training to give, how many
task variations to set, data analysis procedures,
and so on. Moreover, two key metrics are stipu-
lated: total shutter open time (the total time re-
quired to carry out tasks when vision is available);
and resumability (the ratio of total shutter open
time to task time when full vision is provided).
For resumability, there is considerable debate
regarding the merit of the measure. Advocates
believe the metric provides an indication of the
ease by which a task can be resumed following a
period without vision (Baumann et al., 2004).
Critics point out that the metric is also influenced
by the degree to which participants are able to
achieve tasks during occluded (non vision) peri-
ods (Pettit et al., 2006). Consequently, it can be
difficult for a design team to interpret the results
of an occlusion trial.

• Studies often do not report critical data re-

garding the simulator configuration (e.g.
steering sensitivity, max/min acceleration,
driver eye height) which, for given types of
study will be critical in results interpreta-
tion and cross-study comparison.

Occlusion

This is a laboratory-based method which focuses
on the visual demand of in-vehicle systems. Par-
ticipants carry out tasks with an in-vehicle system
(stationary within a vehicle or vehicle mock up)
whilst wearing computer-controlled goggles with
LCDs as lenses which can open and shut in a
precise manner (see Figure 4). Consequently, by
stipulating a cycle of vision for a short period of
time (e.g. 1.5 seconds), followed by an occlusion
interval (e.g. 1.5 seconds), glancing behaviour
is mimicked in a controlled fashion. Occlusion
offers a relatively simple method of predicting
visual demand, but is has been pointed out that
its emphasis on user trials and performance data
means that it requires a robust prototype and is
therefore of limited use early in the design process
(Pettit et al., 2006).

Peripheral Detection Task

This method requires drivers to carry out tasks
with an in-car system (either on road or in a
simulator) and to respond to the presence of lights
within their periphery. The speed and accuracy of