High speed video may be required and was used here. ? To view whether the server is looking at the ball a side view along the base line works well. It would have been better to view from the face side
along the baseline. Front and back views do not work as well in my opinion. The front view is especially deceptive because the eyes are up but you cannot tell where they are looking. Since I could not always see the face I judged either by the head angle (mostly) or by the face profile(sometimes) whether the server was looking at the ball at impact or not. There is still some uncertainty because in the majority of videos the eyes could possibly have been at an extreme angle toward the ball.
The serves - no information on which kind of serve or whether the serve was in.
Results - 60 videos total -
The male servers in this sample were never
observed to be looking at the ball at impact on the serve.
While we have to confirm this observation elsewhere it certainly has changed one on my solid beliefs about watching the ball at impact on the serve................
Sample video with face in profile
Stop action on Vimeo - press play-pause button as fast as possible, not perfect. Better if you can download MP file and view on Quicktime, stop and use QT forward & backward arrows for single frame stop action.
Anyone have data on this issue?