If a player makes a psychic bid and his partner takes a subsequent action that illegally takes into account that the first player has psyched, he is ‘fielding’ the psyche.
To allow for a psyche is not in itself illegal, either if the subsequent auction has exposed partner’s psyche, or if the call that allows for the psyche is the normal action anyway. To ‘field’ a psyche before it has been exposed by an abnormal action is illegal.
In auction 1, if West has four spades and East does not, West has fielded the psyche by failing to support spades. In auction 2, West’s pass of the forcing response exposes the psyche. East can legally proceed on the assumption that West has psyched.