As indicated earlier, detecting aircraft on converging paths can be difficult. The most difficult case is when both pilots are converging at an angle of 60 degrees. Under these conditions both will be relying on their peripheral vision in the area where only motion detection is effective, and this will be hampered by the problems with edge detection as outlined before. Aircraft under these conditions appear motionless and if examined closely can be seen to increase in size. However size again is more of a ‘calculated’ perception and may not be an accurate indicator of the danger present.
Another example of this effect in the soaring environment is seen when two gliders perhaps leave the same thermal in the same general direction but then encounter lift and turn towards each other. Again they can appear relatively motionless flying this pattern, as except for brief moments they remain in each other’s peripheral vision. We see this pattern repeated with a slight variation again with gliders converging on the same thermal following a 60 degree path. In this case it is again difficult to notice that the other aircraft is actually turning and a what rate until it is too late.