and to Discriminate its Velocity The Effects of Early Pattern Deprivation on the Development of the Ability to Detect Local Motion and to Discriminate its Velocity Terri L. Lewis1,2,3, Dave Ellemberg1, Daphne Maurer1,2, Bryan Lee1, Henry P. Brent3, & Alex L. Levin2,3 1McMaster University, 2The Hospital for Sick Children, 3University of Toronto, CANADA PURPOSE MOTION DETECTION SPEED DISCRIMINATION CONCLUSIONS Early pattern deprivation adversely affects the mechanisms underlying motion detection but, at least under some conditions, not those involved in speed discrimination. In agreement with previous findings (Mathews & Qian, 1999; Mathews, Luber, Qian & Lisanby, 2001), our results suggest that, for local motion at 6 deg/sec, speed and direction discrimination are mediated by separate mechanisms which are differentially affected by early visual deprivation. Patients treated for congenital cataract have : normal speed discrimination at 6 deg/sec (this study) abnormal direction discrimination at 6 deg/sec (Ellemberg et al., 2002). To measure the effect of early pattern deprivation on the development of: motion detection speed discrimination To compare the effects of deprivation versus uneven competition between the eyes by testing patients treated for: bilateral cataracts (deprivation) unilateral cataract (deprivation and uneven competition between the eyes) STIMULI 10 deg Gabor carrier spatial frequency = 1 c deg-1 contrast = 100% horizontal (x) and vertical (y) space constant = 5 deg STIMULI Sinusoidal grating (10 x 10 deg) spatial frequency = 1 c deg-1 contrast = 80% velocity = 6 deg/sec PROCEDURE method of limits: is it moving? threshold = minimum speed required to detect vertical motion (mean of 2 ascending and 2 descending thresholds) PROCEDURE 2 alternative temporal forced-choice: which is faster? difference in speed between the two intervals was varied using the Maximum Likelihood staircase procedure (Harvey, 1986) SUBJECTS RESULTS RESULTS Unilateral Bilateral Control n 9 Age 5.1 - 23 yrs M = 11.51 yrs 7.7 - 21 yrs M = 14.34 yrs 4.9 - 23 yrs M = 12.52 yrs Diagnosis of Cataract Dense and central on first eye exam and by 6 months of age N/A Duration of Deprivation 2.0 - 8.2 mo M = 4.5 mo 3.3 - 6.2 mo M = 4.4 mo Patching 2 - 10 hrs/day until age 5 REFERENCES Ellemberg, D., Lewis, T.L., Defina, N., Maurer, D., Brent, H.P., Guillemont, J-P., & Lepore, F. (2002). Greater losses in the sensitivity to second-order local motion than to first-order local motion after early visual deprivation in humans. Manuscript in preparation. Harvey, L.O. (1986). Efficient estimation of sensory thresholds. Behavior Research Methods, Instruments, & Computers, 18, 623-632. Mathews, N., Luber, B., Qian, N., Lisanby, S.H. (2001). Thranscranial magnetic stimulation differentially affects speed and direction judgements. Experimental Brain Research, 140, 397-406. Mathews, N., & Qian, N. (1999). Axis-of-motion affects direction discrimination, not speed discrimination. Vision Research, 39, 2205-2211. Proportion Increase (+ 1 s.e.) Speed (deg/sec) Monocular veiwing with optical correction appropriate for the testing distance. significant deficit (2-fold threshold increase) in both unilaterally (p < 0.01) and bilaterally (p = 0.05) deprived patients no significant difference between patient groups (p > 0.20) patients had normal discrimination thresholds (nonsignificant effect of group, p > 0.40)