How effective are high audio frequencies in commercials in getting audience attention?
I am not aware of any use in using "high audio frequencies" in commercials, but there is a history of making commercials louder (presumably to attract attention). There are laws prohibiting increasing the loudness of commercials  (e.g., CALM Act). Increasing the loudness, without remotely adjusting the volume on the TV is not a trivial thing and potentially involves careful mixing of the audio signals as well as allowing acceptable levels of distortion.