**5. Conclusions**

The current study assessed early attentional and audiovisual processing abilities in typically developing and in Down syndrome infants at 5–7 months of age. The study showed, for the first time, that at such an early age DS infants' attention and audiovisual speech processing is following a different developmental path than typically developing infants. We also observed that audiovisual attention supports concurrent communicative abilities in TD infants, but not in DS infants. In short, the current study demonstrated that early visual attention and audiovisual speech processing might be impaired in DS infants with consequences for their communication development, opening new avenues for early interventions in this clinical population. Furthermore, results from this study suggest that in face-to-face communication, DS infants might need more time to detect/attend to communicative cues, and caregivers might emphasize from early age face-to-face communication as a form of training attention to communicative cues.

**Author Contributions:** S.F. conceived and designed the study. J.P. and C.S. collected the data. J.P. and M.C. analyzed the data. J.P. and S.F. wrote the manuscript. All authors contributed to the article and approved the submitted version. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Fundação para a Ciência e Tecnologia, Portugal (Grant PTDC/MHC-LIN/3901/2014, PI SF) in conjunction with the European Regional Development Fund from the EU, Portugal 2020 and Lisboa 2020 (Grant PTDC/LLT-LIN/29338/2017, PI SF). The APC was funded by Grant PTDC/LLT-LIN/29338/2017.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethical Committee for Research (CEI) of the School of Arts and Humanities of the University of Lisbon (1\_CEI2018).

**Informed Consent Statement:** Written informed consent to participate in this study was provided by the participants' legal guardian/next of kin.

**Data Availability Statement:** The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation, on request to the corresponding author.

**Acknowledgments:** We would like to thank the research assistant Ricardo Sousa for help with data collection, and the audience of the NeuroDWELL workshop, Lisbon, 2019, for comments on a preliminary version of this study. We gratefully acknowledge the collaboration of the Center for Child Development Diferenças in recruitment of participants with Down syndrome, and of all the infants and their families.

**Conflicts of Interest:** The authors declare no conflict of interest.
