Practices grouped under meditation include two families whose instructions point in opposite directions. One narrows attention onto a single object, the other widens it to include whatever appears, and the difference is not a matter of style.
The two instructions do opposite things with attention
Concentration practice selects one object and returns to it each time attention departs, progressively excluding everything else from the field.
Open monitoring gives no preferred object at all, asking instead that whatever arises — sound, sensation, thought — be noticed as it appears and released without being pursued.
One trains the ability to hold a selection against competition; the other trains the ability to register what is present without the selecting step happening at all.
They produce different subjective states
Sustained concentration tends to produce a narrowing and steadying, often accompanied by a sense of absorption in which the surrounding world recedes.
Open monitoring tends towards a wider and more spacious quality, where events are noticed arriving and passing without any of them occupying the centre.
People often prefer one strongly, and that preference usually reflects temperament and current state rather than either practice being more advanced.
Traditional sequencing puts one before the other
Many traditions teach concentration first, on the reasoning that noticing subtle events requires attention stable enough not to be carried off by the first thing it meets.
Open monitoring attempted without that stability tends to become ordinary distracted thinking with a meditative label attached to it.
The sequencing is pedagogical rather than hierarchical, and many practitioners move between the two depending on what a given session seems to need.
Research treats them as distinct interventions
Studies that lump all meditation together produce muddier results than those that separate practice types, because the two families do not affect the same measures.
Concentration practice shows more consistent effects on sustained attention tasks, while open monitoring appears more relevant to how a person relates to their own thoughts.
Programmes taught in clinical settings usually contain both, which is worth knowing when interpreting findings attributed to the programme as a whole.
Which one suits a given situation
A mind that is scattered and agitated often settles more readily with a concentration instruction, because a single clear object gives it somewhere definite to be.
A mind that is dull, or tightly gripped by a single preoccupation, often does better with an open instruction, since narrowing further can reinforce the grip.
Matching the practice to the state rather than adhering to one method regardless is the adjustment experienced practitioners tend to make without being told.