One of the common secrets of an emotionally good melody is that it reflects the inhale-exhale cycle in the human emotional sensitivity. To give relaxation the exhaleing is longer than the inhaling
On the other hand a common harmic cycle in simple improvisation is the 1M 4M 5M cycle (e.g. in Blues)
When we combine these two cycles at the context of melody, we may divide the 7 notes diatonic scale to the ionian 5-chord 1-2-3-4-5 and the mixolydian tetrachord 5-6-7-1'. As the Ionian is longer it may correspond to the exhaling while the mixolydian to the inhaling. My improvising melodies with this duality and over the chord triad 1M 4M 5M we get the emotional effect of inmhaling exhaling.
