A spatial gradient is an attribute of a wormhole.
In 2375, Seven of Nine performed a gravimetric scan of an illusory wormhole created by the telepathic pitcher plant, looking for irregularities in its spatial gradient. However, the sensors returned readings consistent with a class-1 wormhole. (VOY: "Bliss")
Since the bioplasmic organism is unable to affect technology, it presumably manipulated Seven's mind to perceive false sensor data, as it later did to deceive her into believing that USS Voyager had escaped the creature.