This interesting work investigates mutual gaze and its importance as well as influence in human-robot interaction. Thereby, the robot iCub was used which has mechanical eyes. Subjects had to follow iCub's gaze which was either neutral (looking towards the ground) or mutual (looking into subject's eyes). The experiment consisted of multiple blocks with consistent gaze which was assigned randomly at the beginning of the block. After each block subjects were asked to rate their engagement with iCub. Finally, a questionnaire was applied which consists of 5 questions including if participants perceived a difference across the different blocks. The final results show that mutual gaze impacts human-robot interaction positively with respect to engagement and perceiving the robot as more humanoid.

The paper picks up an interesting topic and presents the study settings well with a figure and the used questionnaire in a table. Also the used algorithms and frameworks are outlined sufficiently. Moreover, it is described when participants were excluded from further evaluation. This work gives interesting insight into the importance of gaze in HRI and might have an impact on the further design of humanoid robots and its gaze especially with respect to mechanical robot eyes versus digital robot eyes.

Comments on abstract, title, references

1. Unfortunately, the actual research question is not entirely clear to me just reading the abstract. A sentence such as written in the Conclusion section "We were interested in understanding whether people are sensitive to mutual gaze (while being involved in a different task), whether mutual gaze results in higher degree of engagement, and if it also impacts perceived human-likeness” would give the reader a better understanding of the actual research question from the very beginning.

2. The outlined methodology in the abstract could benefit from slightly more details such as which robot was used and that their focus lies on mechanical robot eyes (as I understood it) as described in the introduction section.

3. An additional subtitle involving mechanical eyes might help to make the paper more impactful.

Comments on introduction/background

1. The introduction section starts with outlining related studies in HRI, their insights in human interaction with robots as well as how important human-likeness and human perception of robots is in HRI. This is followed by related work with respect to infants and mutual gaze which suits perfectly to this work. Afterwards, studies regarding gaze in HRI is described. Thereinafter, the gap of current research which this work should fill is presented by the words “research in this line is not extensive”. Unfortunately, I do not grasp the exact current gap in research from the introduction. The paper would benefit from describing this gap in more detail.

2. Moreover, listing research questions or hypotheses in the introduction or aim of study section, would increase readability and would help to understand faster what actually is investigated.

3. Also, an additional sentence of the aim of the study in the introduction section would benefit the reader to grasp the actually research question as already discussed in the comments on the abstract.

Comments on methodology

1. It would be interesting to know why the handedness of the participants was covered. Is it related to vision?

2. Moreover, referring to Figure 1 while describing the experimental setting in the participants section would help the reader to get an idea of the study settings faster.

Comments on data and results

1. With respect to “Perceived Difference Between Experimental Conditions” only the occurrence of the difference by category are presented but not what the subjects actually perceived as difference in these categories. It would be interesting to know what they perceived as difference and thereby present it as qualitative data.

2. Figure 4 is a nice visualization of the mean ratings. It would also be interesting to know the distribution of the engagement rating (Likert scale) visualized through a Figure.

3. Regarding all performed tests, it is not specified which significance level was applied and whether the tests are one-tailed or two-tailed. By specifying this, other researchers can better understand how significant results are defined in this work.

Comments on discussion and conclusions

1. It would be good if the article would also contain a section “Threats to Validity” to give an understanding which factors might have influenced the participants' answers.

2. The conclusion is short and summarizes important insights of the work. An additional paragraph of describing further work would add further impact on this work.