The effect of weightlessness on the flight behavior of pigeons with canal lesions.

The flight behavior of birds in parabolic flight was studied. Pigeons with labyrinthine lesions were released in weightlessness. Birds with one obstructed labyrinth showed a barbecue spin rotation, with movement directed toward the obstructed labyrinth. The birds with vertical canal blocks showed rotatory movements in the plane of the blocked canals. In weightlessness, the head was in retroflexion and bent over the shoulder, on the side of the obstructed anterior canal. They made tumbling movements backwards around the Y-axis through the skull, and this resulted in a spiral flight pattern. In birds with both the labyrinths obstructed three different phases can be distinguished. The first phase, in which a barbecue spin rotation directed towards the most recently obstructed labyrinth was clear, lasted 1 week. In the second phase this spin behavior is superimposed on a forward tumbling movement: an "outside loop." In the third phase this tumbling phenomenon is the only pattern that remains. The experiments offer not only a model to use in the explanation of the causes of particular vertiginous complaints in human patients, but, furthermore, give an answer to the question of what specific illusions belong to specific vestibular end-organ lesions.