29-31. The sight must be turned away from other objects and fixed on a particular object in order to see it. Otherwise that object will not be perceived in entirety. The fact that the sight is not fixed on it is the same as not seeing it. Similarly is it with hearing, touch, etc.
32. The same applies to the mind in its sensations of pain and pleasure, which are not felt if the mind is otherwise engaged.
33. The other perceptions require the two conditions, namely, elimination of other objects and concentration on the one. But Self-realisation differs from them in that it requires only one condition: elimination of all perceptions.

~ Tripura Rahasya; chapter XVI, verses 29-33