Breathing and Mental Activity
Experience has shown that there is an intimate relationship between the activity of the mind, the feelings and the breathing rhythm . So, the quality of attention, concentration, meditation and contemplation depends on the way we breathe.
 

The rhythms giving best results are many. Amongst these are the 1:4:2 rhythm, which means: inhale air for 1 second, hold the breath for 4 seconds, exhale the air for 2 seconds; and the 4:4:4:4 rhythm, which is called the ‘square’.
 
The latter is free from psycho-physiological disturbances because it is homogeneous. Mental concentration is more powerful when the lungs are motionless. In the 4:4:4:4 rhythm, the stop, or pause, occurs on the second and last 4.

excerpt from "BREATHING AND MENTAL ACTIVITY"
of the 14th Booklet