  This paper describes an experimental study that aims at assessing the actual
contribution of voice system messages to visual search efficiency and comfort.
Messages which include spatial information on the target location are meant to
support search for familiar targets in collections of photographs (30 per
display). 24 participants carried out 240 visual search tasks in two conditions
differing from each other in initial target presentation only. The isolated
target was presented either simultaneously with an oral message (multimodal
presentation, MP), or without any message (visual presentation, VP). Averaged
target selection times were thrice longer and errors almost twice more frequent
in the VP condition than in the MP condition. In addition, the contribution of
spatial messages to visual search rapidity and accuracy was influenced by
display layout and task difficulty. Most results are statistically significant.
Besides, subjective judgments indicate that oral messages were well accepted.
