I found a good comparison online between the interpretation of socionics Si and Ni. I challenge both socionics and MBTI si and Ni doms to take a look and see if it relates to themselves.
"The introverted data gathering functions revolve around self. For the Si, cause and effect are important while the Ni concentrates on interaction and association. The functioning of the body and mind centres in the Si psyche, and the state of the body and mind is a focus for the Ni.
Si is defined in terms of the impact that self makes upon the world and how self can defend against the world, whereas Ni is in terms of the effect the world has on them and the influence they have upon the world - their place within the 'celestial' whole.
For the Ni, the placing of one's self within a context of a whole is divine. Si builds self through practice - starting with basics and progressing to the more refined. Ni builds self through perspective on the order of things, that understanding is more important than skill. The Si considers experiences (including relationships) as validation of their impact on or defence against the world.
The more the Si wins or defends the more self-worth the Si acquires; thus, Si strives constantly for validation and hence, an accumulation of positive experiences. Ni seeks self-awareness and thinks that experiences are fleeting, only a means to an end and they pay little attention to their own physical functioning.
Ni seeks a path to inner space where the mind is isolated from the world, a place of clarity. Security for Ni is having inner peace from where the complexities and confusions of life have little impact. Ni must withdraw in order to cope or discover.
Every experience for Si affirms that they are alive. Si notices every detail about self, but views most of the world cursorily and with scepticism - they focus only on what immediately confronts them. For them, knowledge is less important but skill is paramount so Si will often not attempt to absorb meaning from any of their experiences - they only need to know how to cope.
Si addresses problems by knowing how to tackle them head-on with practiced skill. Ni will step back to address a problem because they need perspective, which would likely be fresh having forgotten a lot of what was done in the past; however, they would remember where they stood on such issues.
Ni seeks to understand their context and they would rather not confront the world so much as bend it toward their perspective. Si is the experience seeker, while Ni is the peace seeker. Ni will have faith while Si will always remain sceptical, never fully trusting the whole. Si fears missing something; while, Ni fears not having meaning. Si may look upon most Ni as lacking useful skill or ability while Ni may look upon Si as being shallow or crass."