Figure 3 shows eye position traces of the viewing eye (A) and nonviewing eye (B) in exotropic monkey S1. During the adaptation paradigm, the viewing eye (left eye) is on target, while the nonviewing eye (right eye) is exotropic with a strabismus angle of 17° to 22°. Even though eye position of the nonviewing eye showed much more variability (SD = 1.56°) than the viewing eye (SD = 0.24°), both eyes followed the same motion pattern. The nonviewing eye also overshot the target in early adaptation, while there were fewer overshoots in late adaptation trials. These adaptive changes are best illustrated using average eye velocity traces. Comparisons of pre- and post-adaptation eye velocity records are shown in
Figure 4. Both the viewing and nonviewing eyes moved conjugately during adaptation, even in the presence of a large-angle strabismus. There is a clear adaptive change in both the viewing and nonviewing eyes post adaptation (
Fig. 4, upper panels).
Figure 5 shows quantitative estimates of smooth pursuit adaptation in the viewing and nonviewing eyes. We calculated initial acceleration as the average eye acceleration in the first 100 ms of smooth pursuit. Individual initial eye accelerations during adaptation across 100 trials were plotted. The normal monkey N1 (
Fig. 5A) showed significant adaptive changes of initial eye acceleration in both the viewing eye (166.2°/s
2 ± 15.7°/s
2, pre-adaptation; 107.1°/s
2 ± 18.5°/s
2, post-adaptation;
P < 0.001, unpaired
t-test) and nonviewing eye (159.8°/s
2 ± 17.5°/s
2, pre-adaptation; 101.8°/s
2 ± 16.6°/s
2, post-adaptation;
P < 0.001, unpaired
t-test). The strabismic monkey S1 (
Fig. 5B) also showed conjugate adaptation in initial eye acceleration for the viewing eye (125.3°/s
2 ± 11.7°/s
2, pre-adaptation; 81.0°/s
2 ± 11.2°/s
2, post-adaptation;
P < 0.001, unpaired
t-test) and nonviewing eye (129.7°/s
2 ± 10.1 °/s
2, pre-adaptation; 83.2 ± 12.0 °/s
2, post-adaptation;
P < 0.001, unpaired
t-test). All the conditions tested (
Table 1) showed significant adaptive changes in initial eye acceleration for both the viewing and nonviewing eyes (
P < 0.001, paired
t-test).
Figure 6 shows comparisons of the percentage change in eye acceleration between pre- and post-adaptation for the viewing and nonviewing eyes. Percentage change in eye acceleration ranged from 32.4% to 47.9% (mean, 38.0% ± 5.8%) in the viewing eye and from 30.3% to 47.3% (mean, 37.6% ± 6.1%) in the nonviewing eye. Mean values of percentage change in the viewing and nonviewing eyes were not significantly different (
Table 1,
P = 0.54, paired
t-test for the whole group).