If we look at the nature of the human mind, we can recognize that there is a designated range of perception, action, knowledge and experience within which it generally moves, and perceptions or mental functioning that falls outside this designated range are not cognised, and in most cases, not even granted any status of reality by most human beings.
The ability of science to penetrate into some of these ranges and bring back factual information that makes it clear that such sub- or super-conscient levels actually exist, makes it clear that the limitation is purely one of the mental being operative here in the field of life and matter, and not an ultimate unreality of those other gradations.
The principle can be clearly illustrated with a few well-known examples. We perceive a spectrum of colors ranging from red at one end to purple at the other. Science has now proven to us that there are however ranges of colors beyond each end of our limited spectrum, in the ranges of infrared and ultraviolet. Devices have been able to record these ranges and find ways to make them available to us. And research shows that various animals or insects, such as honeybees, have the capability of perceiving colors outside the range of the human color pallette. Similarly, the perception of sound is also limited in humans to a specific range. This range can be abbreviated through deterioration of the instruments of hearing, but even in the most perceptive humans, sound above a certain frequency or below that frequency cannot be heard, despite the fact that we know for a fact that certain animals have a keen sense of hearing in ranges outside the human octave; thus, the dog whistle.
Similar to these perception limits, there is the limit of the mental activity that makes certain actions of mind subconscient to the human awareness, and others superconscient to the human awareness. It is no more reasonable to deny the existence of these gradations above and below the human range than it is to nowadays try to deny the existence of colors or sounds in spectrum ranges outside those we can see or hear.
reference: Sri Aurobindo, The Life Divine, Chapter 28, Supermind, Mind and the Overmind Maya