Abstract
From studies using the comparative visual search paradigm it is known that there is a trade-off between inter-hemifield gaze shifts and visual short-term memory (VSTM) when searching for differences between two simultaneous presented displays. These gaze shifts were calculated from eye and head movements between two images. Hardiess, Gillner and Mallot (2008) formed their visual search task by two shelves filled with objects that differed in shape and color. They were presented with a distance between 30° and 120°. The results showed the trade-off based on a smaller number of shifts in greater distance conditions, suggesting higher working memory load. We extended their findings toward more complex materials, namely stills of pendulum clocks. The participants were asked to find differences between two images. The presentation distance varied between 30° and 120°. Furthermore, the factor expertise was varied to examine possible effects of prior knowledge on search effectiveness. As dependent variable we measured inter-hemifield gaze shifts. The experiment comprised two blocks: After the first block, half of the participants were given relevant information about the mechanical principles of a pendulum clock. The other half received irrelevant information. We hypothesized that expert knowledge increases search effectiveness, as participants are able to encode larger information chunks. We were able to replicate former findings with more complex material. An increased distance leads to a reduced number of gaze shifts suggesting both more effort for gaze shifts and more use of VSTM in large distance conditions. Additionally, there was no influence of expertise on search behavior. In both relevant and irrelevant information conditions participants showed higher performance in the second block, suggesting a general change of strategy that is independent of prior knowledge concerning the function of a pendulum clock. Consequently, we infer a powerful robustness of the trade-off effect in comparative visual search tasks.
Supported by LANDESSTIFTUNG Baden-Württemberg grant to MH.