Keine Zahl ohne Zeichen : der Einfluss der medialen Eigenschaften der DGS-Zahlzeichen auf deren mentale Verarbeitung

This dissertation addresses the question whether media-specific features of sign systems have an influence on the mental processing of these signs or not. This research question is investigated with the mental number processing of German deaf signers. The number system in the German Sign Language (Deutsche Gebärdensprache, DGS) differs from German spoken numbers in regard to the visual-spatial language modality. Besides that, the structure of the DGS number system is different from that of Arabic and spoken numbers. This paper shows that the DGS number system is a base-10 one with a sub-base-5. However, this system is language-specific and does not apply for all sign languages. The American Sign Language (ASL) is one example of a visual-spatial language with a pure base-10 number system. German signers are familiar with the processing of base-10 Arabic numbers as well as the processing of written German numbers. Thus, German signers are not only using three different number symbol systems but also two different number systems. In this dissertation, the processing of those different symbol systems in German deaf signers is examined systematically by means of seven empirical studies regarding several important number-processing effects (SNARC effect, MARC effect and distance effect). A comparison of the results of the German deaf group with those of US-American deaf as well as those of hearing German participants should give some answers to the question which aspects of number processing are linked to language modality and which are associated with a language-specific number system. The results indicated format-specific differences in the processing of base-10 number systems on the one hand and the DGS number system on the sub-base-5 on the other hand. In a parity decisions task with DGS numbers the parity status of the dominant handshape seemed to be more relevant for reaction time patterns than the parity status of the whole number sign. This was observed in the DGS and written German number judgments by German signers. It was also partly true for some participants judging Arabic numbers, but not for the judgment of dot patterns. Moreover a DGS-specific distance effect was observed. In magnitude comparisons with a fixed standard of five the reaction times for the numbers four and six (5 +- 1) were very slow, but the mean reaction times for all other number comparisons did not differ significantly from each other. This DGS-specific distance effect was exclusively observed when German signers judged DGS or written numbers, but not in the results patterns of Arabic numbers or dot patterns. Since the result patterns for the DGS numbers and the written numbers were very similar, it was assumed that written numbers are encoded by German deaf signers via an inner signing. Both effects were observed for German signers only, not for US-American signers or hearing German participants; this substantiated the assumption that those effects were related to the sub-base-5 structure of the DGS number system. These DGS-specific effects raised the question whether DGS and Arabic numbers are processed via the same cognitive structures as is assumed for the hearing population (e.g. Dehaene, 1997; Nacchache & Dehaene, 2001; Nuerk, Wood & Willmes, 2005). The results of a cross-notational priming study with German signers supported this assumption. However, the same study showed that there was no reaction facilitation when a DGS number was primed with exactly the same DGS number. This lack of a priming effect was explained with interferences between the motor programs involved in language perception and those motor programs controlling the bimanual key presses necessary for supplying an answer to the experiment. Further indications for this kind of interferences were observed in the results patterns of the number magnitude comparisons of both deaf groups. Since there were no visible SNARC effects, it was assumed that the SNARC effect can be overlaid by those interferences. On the whole, there were clear links to an influence of the media-specific features of the DGS number system on mental number processing. Probably similar format-specific effects have not yet been observed for the hearing population because there are no differences in the main structure of the Arabic number system and the number systems of the investigated languages