Dear Aenne, some papers:

Article Junior plastic surgeon's confidence in aesthetic surgery pra...

Article Why Do Females Use Botulinum Toxin Injections?

Article The Impact of Facial Lipofilling on Patient-Perceived Improv...

According to Christopher Alexander, beauty is what exists in space and matter, not just what is in human cognition. I subsequently developed a mathematical model of beauty that can help address (1) why a design is beauty, and (2) how much beauty the design has, so the model can act as a beautimeter:

https://www.researchgate.net/publication/272159333_Wholeness_as_a_Hierarchical_Graph_to_Capture_the_Nature_of_Space

https://www.researchgate.net/publication/299337109_A_Mathematical_Model_of_Beauty_for_Sustainable_Urban_Design

More recently, I brought a complex network perspective to the notion of beauty, wholeness, or life, which can be used interchangeably:

https://www.researchgate.net/publication/296396310_A_Complex-Network_Perspective_on_Alexander%27s_Wholeness

Currently, we have been developing more analytical insights and evidence to support the wholeness oriented design.

Article Wholeness as a Hierarchical Graph to Capture the Nature of Space

Presentation A Mathematical Model of Beauty for Sustainable Urban Design

Article A Complex-Network Perspective on Alexander's Wholeness

Rolf Reber (University of Oslo) is doing research on art appreciation, he did a presentation about neuroscience and art as well. Might help?

Confidence is not a very big topic in aesthetic research, but there are some apers from the very applied part of aesthtics, e.g. surgery:

Sterodimas, A., Radwanski, H. N., & Pitanguy, I. (2009). Aesthetic Plastic Surgery: Junior Plastic Surgeons' Confidence in a Training Program. Aesthetic Plastic Surgery, 33(1), 131-132. doi: 10.1007/s00266-008-9299-3

best,

CCC

 Thanks a lot for all your answers,

it's another case where I am astonished to see no direct investigations yet, but it seems the field is so young that opportunities are endless (taking the positive perspective here).

I was wondering whether one might not at least take response time as an approximate measure? Yet, RTs are not a standard measure to be taken in aesthetics.