If visual attention is managed by interacting reflexive and voluntary systems, we can make two conclusions:
1. A driver can never completely ignore visual onsets in his/her periferal vision, so long as the onset causes a sufficient change in light energy.
This suggests that placing auxiliary displays so that the road is within periferal vision has mixed consequences. It would be good for the React switch, since reflexive eye movements would tend to facilitate rapid response to road conditions. However, it would also mean that visual onsets within the display would reflexively draw attention (and possibly eye motion) regardless of the driver's explicit attentional goals. This would increase the danger of inappropriate Notify events. If this is true, interaction designers must take care to avoid visual onsets except when the driver is already viewing the display. At other times, onsets must be performed in a way which minimizes reflexive attention shifts -- perhaps by using a technique that causes minimal change in light energy.
2. Voluntary processing can affect reaction times for visual onsents even when the onset provokes a reflexive response.
This mitigates the effects of the first conclusion. Although an onset may disrupt the driving task, it is unlikely to completely disengage the driver's attention unless he/she consciously participates. Unfortunately, the converse is also true. If the driver is engaged in an information task, he/she may not fully switch attention to an onset that is critical to driving. Even if the React switch occurs, performance could be significantly hampered if the driver is reluctant to shift attention.
This article is also referenced from McFarlane and Latorella (2002) in the following paragraph:
Any design solution that implements the negotiated interruption method for coordinating user interruptions must have a mechanism for getting users' attention while they attend some other activity. Users must be notified of incoming interruptions, so they can control when or whether to handle them. People's attentional focus is vulnerable to certain kinds of stimuli (Müller & Rabbitt, 1989). ...