We investigated whether individuals with congenital nystagmus (CN) hav
e abnormalities in motion perception and whether any such abnormality
could be due to their nystagmus or to adaptive mechanisms to avoid osc
illopsia. CN and control subjects performed motion detection and discr
imination tasks. In the detection tasks, subjects reported the onset o
f motion and drift direction in either a vertical or horizontal direct
ion. In the discrimination task, the stimulus was a high-contrast grat
ing and moved vertically. Subjects judged whether successively present
ed reference and test velocities were the same or different, using a f
orced choice instruction. Vertical velocity detection was normal in th
e patient group. The vertical velocity discrimination task showed that
the patients were less accurate than the controls, especially when ve
locities were slow. Horizontal velocity detection thresholds were rais
ed in the patient group regardless of the direction of the slow phase
velocity (spv) of the nystagmus. Evaluation of eye movement recordings
performed during the task demonstrated that detection velocity was hi
ghest when stimulus motion and spy were in the same direction. When ny
stagmus was absent due to a prolonged neutral zone, thresholds did not
reduce to normal values. The findings show that the image motion caus
ed by the nystagmus cannot account for all the abnormalities found. De
ficits occurred in the absence of nystagmus and when motion was orthog
onal to the meridian of the nystagmus suggesting that the suppression
of motion perception is, in part, due to adaptive mechanisms used to a
void oscillopsia.