I will start off by saying i am a scientist, but we also don't understand human psychology all that well. Its all manifestations of this.

I wouldn't think the shuffling is the subconscious manifestation -- humans are bad at this -- however, i would say that the images do prompt the imagination. That is why one needs a proper deck, like Waite Smith, in that the artist is guiding your reading.

A tarot reader once told me its about what symbols or imagery in a card that first jumps to mind. That itself does seem to be a manifestation of the subconscious.