Talking numbers – Language influences on number processing in different stages of life – TALKNUM

TALKNUM uses behavioral and neurofunctional (fMRI) measurements in French and German-speaking participants, and neurostructural measurements (lesion-behavior mapping and disconnectome mapping analyses) in German-speaking stroke patients.

In a first study, we systematically targeted linguistic influences on multi-digit Arabic number processing in French and German-speaking participants by comparing behavioral performance in two-digit number magnitude comparison (Milon et al, under review). The unit-decade compatibility effect (UDCE) - an interference effect from the irrelevant unit digit indicating decomposed processing of Arabic digits – did neither differ between German- and French-speaking participants nor within French-speaking participants for numbers smaller or larger than 60. However, overall response latencies significantly differed in French participants for number magnitude comparisons below and above 60. As this difference was not observed in German-speaking participants, it can only be explained by influences due to the vigesimal number word system in French.
In a next study, we replicated not only that the UDCE was unaffected by number word system, but also identifed a vigesimal equivalent, the unit-vigintade compatibility effect (UVCE) for numbers larger than sixty (Janssen et al., in revision). The UVCE indicates that the number word was processed and that the number’s constituting unit and decade words were compared independently from the digits’ magnitudes of the number. We also observed an additional effect pointing to number word processing: participants responded faster to within-vigintade items (86 vs. 95) than to between-vigintade items (76 vs. 85). This effect can only be explained by participants’ access to the number word so that the decades were identical.
Together with our German collaboration partners (Hans-Otto Karnath, Tübingen; Stefanie Jung, Trier) we used lesion-disconnectome mapping in stroke patients to target the neural correlates of verbally-mediated number processing such as the learning and the retrieval of arithmetic facts (Smaczny et al., 2025). We found that hippocampal disconnection from the left-hemispheric language network selectively disrupted new multiplication fact acquisition. Since some of the older control participant data for our patient study were acquired web-based, we also investigated possible test mode effects in older participants together with our German collaboration partner Stefanie Jung (Trier). In this study we could show that the standard neuropsychological tests used were not affected by the web-based testing environment (Janssen, Jung & Klein, in press).

Using fMRI will allow us to triangulate the neural correlates for the UDCE and the UVCE and to examine whether language (sub)processes are involved.

Published peer-reviewed articles
1. Janssen, R.J., Klein*, E. & Jung*, S. (in press). Biases in online vs. paper-pencil number line tasks in older adults. Acta Psychologica.
2. Smaczny, S., Jung, S, Willmes, K., Karnath, H.-O. & Klein, E. (2025). Arithmetic fact retrieval deficits in chronic stroke – a deficit of relearning? Cortex (192), 78-89.
Under review/in revision peer-reviewed articles
1. Janssen, R., Knops, R., Viarouge, A. & Klein, E. (re-submitted after major revisions). When numbers whisper their names – number word processing in multi-digit number magnitude comparison in French speakers. Open Mind.
2. *Milon, L., *Janssen, R., Sasso-Sant, M., Jung, S. & Klein, E. (submitted) Language influences in two-digit number processing across German and French.
*contributed equally
Conference presentations
1. Milon, L., Janssen, R., Sasso-Sant, M., Jung, S., Klein, E. (2026, March). A ghost in the machine: number words influence two-digit magnitude comparison performance in French. Annual meeting of the General Psychology section of the German Psychological Society (TeaP), Trier, Germany. [Poster]
2. Klein, E., Smaczny, S., Jung, S., Willmes, K. & Karnath, H.-O. (2024, July). Neural correlates necessary for (re)learning arithmetic facts – causal evidence from chronic stroke patients. Meeting of The International Mind, Brain and Education Society Conference (IMBES). Leuven, Belgium. [Talk]
3. Janssen, R.J., Knops, A., Viarouge, A. & Klein, E. (2026, March). Linguistic influences on two-digit number processing in French speakers. Annual meeting of the General Psychology section of the German Psychological Society (TeaP), Trier, Germany. [Talk].
4. Klein, E., Knops, A., Viarouge, A., Wortha, S., & Janssen. R.J. (2025, September), Linguistic Processing in Multi-Digit Number Magnitude Comparison – The Base-20 Effect in French-Speakers. 24th Conference of the European Society for Cognitive Psychology. Sheffield, United Kingdom. [Poster]
5. Janssen, R., Viarouge, A., Knops, A., Klein, E. The unit-decade compatibility effect in an analogue magnitude comparison task. Mathematical Cognition and Learning Society Conference (MCLS), Jun 2025, Hongkong, China. [Talk]
6. Janssen, R.J., Knops, A., Viarouge, A. & Klein, E. (2025, June). Influences of number word syntax on the processing of two-digit numbers in French speakers. Mathematical Cognition and Learning Society Conference (MCLS) 2025. Hongkong, China. [Poster]
7. Janssen, R.J., Knops, A., Viarouge, A. & Klein, E. (2024, July). Symbolic and Physical representations of numbers in a double-digit Number Comparison Task. Meeting of The International Mind, Brain and Education Society Conference (IMBES). Leuven, Belgium. [Poster]
8. Janssen, R.J., Knops, A., Viarouge, A. & Klein, E. (2024, April). Linguisitic influences on number processing in a two-digit number comparison task. Workshop Relations between space, language, and numbers. Tuebingen, Germany. [Poster]

Acquiring number words is crucial for developing good numerical competencies. Linguistic irregularities of number naming systems, such as inverted number words (e.g., the German number word for 32 translates to “two-and-thirty”), affect numerical skills and their development, and language impairments can be associated with impaired numerical processing. The relationship between language and number processing, however, is still discussed. Crucially, the scientific discourse and the transfer of study results across nations are aggravated by the varying number word syntax and their transparency.
Talking Numbers (TALKNUM) takes a cross-linguistic approach to specify the association of language and number processes in French and German. Both languages are particularly suited because they cover different levels of number word syntax complexity (i.e., transparent, intransparent with low complexity, intransparent with high complexity). We capitalize on these complexity differences to conclude (cross-)linguistic influences on the different levels of place-value processing (i.e., place-value identification, activation, and manipulation) and relate these levels to individual language skills at the three linguistic layers (i.e., phonology, morphology, and syntax). Our research in TALKNUM will investigate these relationships on a behavioral, neurofunctional (fMRI), and neurostructural level (MRI using univariate and multivariate lesion-behavior mapping as well as disconnectome mapping analyses) in French and German-speaking participants for a direct comparison of both number word systems. Three age groups (i.e., children, adults, and older adults) will be recruited to gain knowledge on age-related changes. In addition, the effect of typical and impaired language processing (children with and without developmental language disorders and stroke patients) will be evaluated. Knowledge gained from this project is vital to conclude the effect of language in general and language impairment on number processing in particular. By systematically evaluating neurofunctional and neurostructural correlates underlying common subprocesses of linguistic and number word processing, this research will contribute to theoretical knowledge of how and at what level of place value processing linguistic levels are intertwined. This knowledge will aid in developing specific cross-domain therapeutic approaches for number and/or language disorders in diverse populations.