ON THE FIGURE-TO-GROUND PHENOMENON: A TEST AND ITS ANALYSIS

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1 ON THE FIGURE-TO-GROUND PHENOMENON: A TEST AND ITS ANALYSIS Olga Waelder and Manfred F. Buchroithner Institute for Cartography Technical University of Dresden ABSTRACT The figure-to-ground phenomenon is one of the fundamental organising concepts in visual perception. In Waelder and Buchroithner (2003) a first idea for a quantitative approach for the decision function figure-or-ground is presented. In the present paper a test with eight different land/water grey scale representations will be described. These presentations differ as well in the contrast and in the relative positions of a lighter object in comparison with a darker one as in the kind of maps: six presentations out of eight belong to an unknown, imaginary land/water map and two other show a map of Italy in its usual and in a transformed position. Are there defined contrast and position combinations, which result in a land/water, land/land or water/water decision? Does a lighter object influence the decision to be land, if it is placed on the top of maps? These and some other test results will be analyzed and commented. In addition the authors assume, that the indicator a map is recognized as wellknown influences the decision land/water without any effects of other indicators like contrast or position. INTRODUCTION The figure-to-ground phenomenon is one of the fundamental organising concepts in visual perception. This topic is popular and has often been investigated from different point of views. If a figure cannot be separated from the ground, we are not able to recognize it. Clear separation of figure and ground allows to achieve multiple levels of information accessibility, and to direct attention to limited aspects of information while providing the geographic context necessary for a sensible, meaningful interpretation. The results of the study by MacEarchren (1992) do not support the main hypothesis that darker areas are seen as figure (c.f. Robinson et al. 1984), nor do they support Arnheim s contention that lighter is figure (see Arnheim 1959, 1964). In addition to the lack of a relationship between absolute brightness and figure perception, the knowledge about which area represents land and which water seems to have little effect on figure identification. In Waelder and Buchroithner (2003) a first idea for a quantitative approach for the decision function figure-or-ground was presented. In accordance to Lakoff s conceptual metaphor, it results in the fact that knowing is seeing (c.f. Lakoff 1993). So, we are able to recognize and define something only, if we see it or, in other words, if we can distinguish a figure from its background. We also think, that a-priori information about what should be perceived plays important role. A priori information about what should be seen is considered and calculated by using significant points. Hence, we modified Lakoff s statement via knowing is more than seeing to knowing is seeing plus understanding. In this paper a test is presented and its results are analyzed and commented: Are there defined contrast and position combinations which result in a land/water, land/land or water/water decision? Does a lighter object influence the decision to represent land, if it is placed on the top of maps? What are the results for a well-known land/water combination? And further, are there any knowledge-specific differences in the answers of the two student groups: economists and geoscientists? TEST DESCRIPTION For the test eight different land/water greyscale representations have been produced (see Fig. 1). These presentations differ in contrast and in the relative positions of the lighter and the darker objects: six presentations belong to an imaginary land/water map and two others show Italy in its usual and in a transformed position.

2 Our objective was to test two groups of the students (144 economists and 144 geoscientists with their majors in geodesy, cartography, geography and hydrology) regarding their land/water perception and their reaction on wellknown forms of land/water combinations. The four questions were the following: a) I think, I know this landform (Yes/Now) b) This is the map of two bordering lands (Yes/Now) c) This is the map of two bordering water areas (Yes/Now) d) This is the map of a land/water area (Yes/Now) It was allowed to give the answers for b) - c) totally independent of each other. Hence, it was possible to get three Yes. In order to get rid of the short-time memory impression of the previously considered maps, we used non-transparent office notes (stickers) to cover all maps. The students were then requested to work totally by themselves autonomously with a single unveiled map and to keep the other maps hidden. Figure 1. Example of test maps with answer boxes. In order to visualize their land/water decision, the students then had to mark their maps with the letters L and W, provided they answered the fourth question with yes. Although some students did not follow the instructions (for example, they did not keep the maps covered, they worked in small groups or spoke with their neighbours), the obtained results are interesting and seem to be relevant. In the following section, we present some of them. RESULT After the first selection of all correctly completed questionnaires only the 121 tests in the economists group and 117 tests in the geoscientists group remained. Those were considered suitable for further statistical analysis. First, the authors assumed, that the indicator a map is recognized as well-known (in our case the map of Italy) biases the land/water decision regardless the influence of other indicators like contrast or position. Indeed, there are 19 tests in the economists and 13 tests in the geoscientists group, where the outline of Italy in either north-oriented or specially transformed form was marked as unknown. Amongst them, there are 5 tests of the economists group and one test of the geoscientists group (a student joke?) with this statement even concerning the north-oriented form of Italy. This results

3 in approx. 96 % of the economists and in over 99 % of the geoscientists, which recognized the usual, north-oriented map of Italy. Thus, the importance of basic geo-knowledge could be confirmed. The other fake maps have a certain similarity to the Korean peninsula. Its outline was transformed into an absolutely symmetric map. It is clear that the map of Korea cannot be classified as well-known but is specially known to geoscientists. It is interesting that there were two geoscientists who wrote under these imaginary maps Korean Peninsula. In this case the indicator I certainly know this land was stronger than the indicator This land map shows an unusual symmetry! Second, the authors wanted to proof, whether the defined contrast and position combinations result in a land/water, land/land or water/water decision. Table 1 presents some results for both groups corresponding to six fake maps. Map / Questions (a) (b) (c) (d) % % % % % 5.13 % % % % 4.96 % % % 9.40 % 0.85 % % % % 9.92 % % % % 5.98 % % % % 3.31 % % % 5.98 % 0.85 % % % % % % 6.84 % 2.56 % % % 8.26 % % % % 1.71 % % 6

4 Table 1. Comparison of test results (upper line economists, lower line geoscientists, Yes answers in percents). Further, a preference for the indicator The land is the darker area can be seen, which reached up to % (map 3) for the economists and up to % (map 1) for the geoscientists. In addition, the white area in map 6 is seen as land by % of the economists and by % of the geoscientists. Most interesting is the fact, that the strong difference in the results of both groups is subject to the indicator The land is reaching down from the top of the map under the condition, that the land is known (a-priori knowledge), c.f. Table 2. It has to be noted, that for the complementary indicator The land is reaching down from the top under the condition, that the land is unknown there exist no significant differences. Probably, in this case the basic or apriori knowledge of geoscientists plays an important role. Map no Land is reaching down from the top under the condition, that the land is known % % % % % % % % % % % % Table 2. Results for an apriori knowledge indicator. Upper line: economist group; lower line: geoscientist group. OUTLOOK AND DISCUSSION It seems to be justified to state that our initial hypothesis about the influence of apriori or background knowledge ( Knowing is seeing plus understanding ) is confirmed. It is highly probable, that the indicator Land form is known is stronger than both the indicator Land form is symmetric and the contrast of maps. It is planned to continue this research. In particular, future tests have to be improved, also in terms of possible error sources. ACKNOWLEDGEMENTS The authors thank Prof. Naether, Institute for Stochastics, Freiberg University of Mining and Technology (Germany) for his helpful co-operation. REFERENCES Arnheim, R., Visual Thinking, Berkeley, CA: University of California Press, (1969) Arnheim, R., Art and Visual Perception. CA: University of California Press, (1974) Lakoff, G., The Contemporary Theory of Metaphor., (ed. A. Ortony) Thought and Metaphor. Cambridge, Cambridge UP (second edition), pp , (1993) MacEachren, A.M., T.A. Mistrick, The role of brightness differences in figure-ground: Is darker figure? 29, The Cartographic Journal, pp , (1992) Waelder, O., M.F. Buchroithner (2003), Figure-to-Ground Phenomenon and Fuzzy-Theory. Proceedings of 21th ICC, Durban, July 2003.

5 BIOGRAPHY OF THE PRESENTING AUTHOR PROF. MANFRED F. BUCHROITHNER Dr. Manfred F. Buchroithner is Full Professor of Cartography at the Institute for Cartography (IfC) of the Dresden University of Technology (TUD). He holds degrees in both Geology & Paleontology (Graz, Austria) and Cartography and Remote Sensing (ITC, NL) and obtained his PhD in Out of his more than 250 articles more 60 have been published in reviewed journals. Moreover, he has written three books and edited three volumes on remote sensing. For 4 years ( ) Prof. Buchroithner served as Vice Chairman of EARSeL, the European Association of Remote Sensing Laboratories. In spring 1999 he was appointed Secretary General of EURO-STRIM, the European Association mandated to operationalise the European Doctorate in Space Technologies for Risk Management. For 7 years he was permanent lecturer at the U.N. Course "Remote Sensing for Educators" at the University of Stockholm. At the IfC he introduced short courses in Presentation Techniques and Project Management. In 1994 Prof. Buchroithner was awarded the honorary title of a "Euro-Ingenieur" for his postgraduate teaching activities and he was elected Full Member of the German Geodetic Commission at the Bavarian Academy of Sciences. In 2002 he was elected Member of the Academy Institution "Arbeitsgemeinschaft fuer vergleichende Hochgebirgsforschung" in Munich. He has been permanent reviewer of the German Research Council (DFG) since 2000 and received several academic awards and honours, amongst them 3 "Best Map Awards" of the Internat. Cartograph. Association.