You can find our recent paper below, presented at​ CogSci 2020, on the processing of multimorphemic Turkish words. 
erginmorganodonnell_2020.pdf
File Size: 249 kb
File Type: pdf
Download File
erginmorganodonnellcogsci2020_poster.pdf
File Size: 654 kb
File Type: pdf
Download File
 
​Some background:
​
Whether morphologically complex words are stored as a whole or decomposed into constituents has been well-investigated experimentally in Indo-European languages like English, Italian, Dutch and French. There is substantial evidence in these languages in favor of a dual-route architecture, allowing words to be decomposed and stored as wholes (e.g., Burani & Caramazza, 1987; Taft, 1994; Cole, Beauvillain & Segui, 1987; Baayen, Dijkstra & Schreuder, 1997; Caramazza, Miceli, Silveri, & Laudanna, 1985, etc.) .  
To date, however, the vast majority of the research on this topic has come from Indo-European languages that contain relatively simple morphological systems. Although these ‘analytic’ languages permit various morphological processes such as prefixation, suffixation, and compounding (in some cases with linking morphemes), the absolute complexity that words exhibit is rather limited. For example, although English words may contain multiple prefixes and suffixes (e.g., non-de-compos-ition-al), consultation of the English Lexicon Project (‘ELP’; Balota, et al., 2007) reveals that English multimorphemic words contain only 2.5 morphemes on average. Furthermore, these languages contain relatively few multimorphemic words (the ELP lists a little over 50,000 for English) and many irregular and opaque forms, facts that may bias readers to rely on whole-word storage, even for regular/transparent forms. It thus could be the case that the consistency of the findings in favor of dual-route/dual-representation systems may be an artifact of the morphologically-impoverished languages that have been studied to date.
Turkish, on the other hand, is an Altaic agglutinative language that allows words to be made from long strings of morphemes that would typically be expressed in Indo-European languages with sequences of words (see the table below). The complexity of Turkish morphology compared to most Indo-European languages is staggering. For example, Hankamer (1989) estimates that an average multimorphemic word contains 4.8 morphemes in Turkish and that each verb can have over 2,000 inflectional forms—given a lexicon of 10,000 verb roots and 20,000 noun roots, Turkish could potentially contain over 200 billion lexical forms. 
In theory, the sheer size of the Turkish multimorphemic vocabulary may limit the number of forms that can be stored as wholes. In addition, the fact that Turkish is morphologically regular may bias the use of decomposition. However, there are only a few experimental studies conducted in Turkish so far (e.g., Gurel, 1999). 


References:
1. Baayen, R. H., Dijkstra, T., & Schreuder, R. (1997). Singulars and plurals in Dutch: evidence for a parallel  dual-route model. Journal of Memory and Language, 37, 94–117.
2. Balota, D. A., Yap, M. J., Cortese, M. J., Hutchison, K. I., Kessler, B., Loftis, B., Neely, J. H., Nelson, D. L., Simpson, G. B., & Treiman, R.(2007). The English Lexicon Project. Behavior Research Methods, 39, 445-459
3. Burani, C., & Caramazza, A. (1987). Representation and processing of derived words. Language and Cognitive Processes, 2, 217–227.
4. Caramazza, A., Miceli, G., & Silveri, M.C. (1985). Reading mechanisms and the organisation of the lexicon: Evidence from acquired dyslexia. Cognitive Neuropsychology, 2, 81-114.
5. Colé, P., Beauvillain, C., & Segui, J. (1989). On the representation and processing of prefixed and sufixed derived words: A differential frequency effect. Journal of Memory and Language, 28, 1–13.
6. Gürel, A. (1999). Decomposition: To what extent? The case of Turkish. Brain and Language, 68 (1–2), 218–224.
7. Hankamer, J. (1989). Morphological parsing and the lexicon. In W. D. Marslen-Wilson (ed.), Lexical representation and process, pp. 392–408. Cambridge, MA: MIT Press.
8. Taft, M.  (1994). Interactive-activation as a framework for understanding morphological processing. Language and Cognitive Processes, 9, 271-294.
​