Digital display apparatus with dual refresh frequencies

A digital display apparatus comprising:

• a controller;
• and
• a digital pixel panel,
• wherein:
• a plurality of pixels of the digital pixel panel are divided into a first group of pixels and a second group of pixels,
• the controller is configured to display a graphic content via the digital pixel panel,
• the controller is configured to operate the first group of pixels at a first flicker-free refresh frequency (F1)≥60 Hz,
• the controller is configured to operate the second group of pixels at a second flicker-free refresh frequency (F2)>F1, and
• when the graphic content displayed on the digital pixel panel is viewed by a subject, an invisible visual stimulation at a harmonic frequency (HF) equal to |2F1−F2| is induced endogenously in a brain of the subject, wherein, HF is either:
• between 20 Hz and 45 Hz, or
• between 3 Hz and 10 Hz;
• and
• wherein the digital display apparatus operates at one of a plurality of combinations of F1 and F2 other than a combination of F1 and F2 in which F1=80 Hz and F2=120 Hz.