The Effect of Structure on Object-Location Memory

The Effect of Structure on Object-Location Memory Carsten Winkelholz (winkelholz@fgan.de) Christopher Schlick (schlick@fgan.de) Mark Brutting (bruetting@fgan.de) Research Establishment for Applied Science (FGAN) Research Institute for Communication, Information Processing and Ergonomics Neuenahrer Strasse 20 53343 Wachtberg, GERMANY The effect of layout structure on object-location encoding and retrieval could best be investigated if a computational model of human spatial cognition is considered. Recently some compelling works toward this goal has been published (Wang et al 2002; Johnson et al 2002). This paper shows one application area for computational models of human spatial memory, but also sheds some new light on the requirements of such a model. Abstract This paper aims to study the effect of structure in a graphical layout on object-location memory. In two experiments several structures have been examined in respect to the performance of object-location retrieval. The results show that beside simple object-to-object spatial relations also the spatial relation of three objects is encoded in human spatial memory as a noisy distance-angular pair. Further the results show that noise in spatial memory is not symmetric, but seems to be distorted towards a higher accuracy to the horizontal directions. Design of the Experiments Introduction One aspect of human spatial memory is the usage of allocentric frames of references to encode and retrieve the location of an object. This aspect of human spatial memory implicates that the structure of a graphical layout might affect the performance of object-location encoding and retrieval. Basically the study presented in this paper is motivated by some experiments performed recently in the community of information visualization. One experiment of Travanti & Lind (2001) investigated object location memory in hierarchical information structures across different instances of 2D and 3D displays. The results of their tests show, that the 3D display improves performance in the spatial memory task they designed. They were aware that their result does not prove their hypothesis that the natural appearance of the 3D display used in the test actually affected the improved performance. They speculated that possibly other visual properties of an item in the 3D display were used as a reminder for the memory task. Cockburn (2004) showed that neither the natural appearance nor the different sizes of the items in the 3D display affected the performance of object-location retrieval. In both studies the memory task was to associate alphanumerical letters to the items. Therefore Cockburn suspected that the vertical orientation of Travanti & Lind’s 2D display made the formation of effective letter mnemonics more difficult than the horizontal 3D layout, because words and word combinations normally run horizontally left to right. By analyzing these studies we came to the conclusion that one major factor had not been considered - the factor of the object-to-object spatial relations (the structure of the graphical layout respectively). The papers cited above inspired the design of the experiments in this study. There were two phases in the cited experiments. In the encoding phase the subjects had to learn associations of alphanumerical letters to one object in the structure. During the encoding phase a click on one of the objects in the display highlighted the object and revealed a letter at the top of the display, which had to be associated to the position of the object. In the retrieval phase the subjects had to find all of the letters, one at a time. A randomly selected letter had been shown at the top of the display area, and the subject had to click the object associated with it. This design of the experiment has two drawbacks. First the subjects are free to choose the objects in the encoding phase and second that alphanumerical letters are used as retrieval cues. The first point gives subjects the opportunity to develop strategies for learning the object-letter associations. In combination with the usage of alphanumerical letters this increases the probability that subjects create mnemonics through possible abbreviations of words that can be read from a row. In respect to a cognitive model these are task specific aspects. The study of this paper was interested in more general mechanisms of object-location encoding/retrieval. To meet this goal the design of the experiment had to prevent subjects from further processing object-locations in the encoding phase. This suggested the task of memorizing a randomly created sequence of highlighted objects from the structure. The number of correct repeated sequences is used as a measure of performance. Furthermore allows this kind of memory task an effective analysis of the errors subjects make. Two experiments were performed. The first experiment investigated the factor horizontal vs. vertical orientated