1. 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
yrs
M = yrs
yrs
M = yrs
yrs
M = yrs
Diagnosis of Cataract
Dense and central on first eye exam and by 6 months of age
N/A
Duration of Deprivation mo
M = 4.5 mo mo
M = 4.4 mo
Patching
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,
Mathews, N., Luber, B., Qian, N., Lisanby, S.H. (2001). Thranscranial magnetic stimulation differentially affects speed and direction judgements. Experimental Brain Research, 140,
Mathews, N., & Qian, N. (1999). Axis-of-motion affects direction discrimination, not speed discrimination. Vision Research, 39,
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)