There were no statistical differences in gender (female/male: 17/28, 25/17, and 10/12 in patients, relatives, and controls, respectively; χ2 =4.2, p=0.12), ethnicity (Caucacian:African American:others: 24:20:1, 18:21:3, and 15:5:2, respectively; χ2 =6.0, p=0.20), and years of education (mean ± SD: 11.5 ± 2.0, 15.3 ± 13.6, and 14.5 ± 1.9, respectively, F(2, 108) = 2.23, p = 0.11). Differences in age were marginally nonsignificant (38.7 ±12.6, 43.0 ± 11.0, and 35.8 ± 13.3, respectively; F(2, 108) = 2.83, p=0.06).
There was no significant effect of target direction on dependent measures; therefore data were collapsed across directions. Stabilized pursuit was not triggered in 2.4% of the trials, while in 88.2% of the trials stabilization was triggered in the first, 8.4% in the second, and 0.9% in the third “zero velocity window”. The percentages were nearly identical in the 3 groups (p > 0.05).
For predictive acceleration, there was a significant main effect of group (F(2, 129) = 5.43, p=0.006) and velocity (F(1, 135) = 74.92, p<0.0001), but no significant group by velocity interaction (p=0.25) or effect of age (p=0.84). Note that the effective degree of freedom was estimated by Kenward-Roger approximation in the mixed model to account for within family correlation. Post hoc tests showed that schizophrenia patients (p= 0.004) and non-schizophrenia relatives (p= 0.04) had reduced acceleration compared to the healthy controls (). Patients and relatives were not significantly different (p=0.65). The differences were more prominent at (expected) target velocity of 18.7°/s (patients vs. controls, p=0.01; relatives vs. controls, p= 0.03) as compared to 10°/s (patients vs. controls, p=0.16; relatives vs. controls, p= 0.56). Removing age as a covariate did not change the significance levels (patients vs. controls, p=0.02; relatives vs. controls, p= 0.02 for 18.7°/s and patients vs. controls, p=0.61; relatives vs. controls, p= 0.93 for 10°/s).
Comparisons of smooth pursuit measures (mean ± S.E.) in schizophrenia patients, non-schizophrenia 1st degree relatives, and healthy controls.
Reduced eye velocity in patients and relatives emerged early in the acceleration phase (). This was confirmed using the 50 ms epoch data. For 18.7°/s, group differences emerged at the 50–100ms epoch after stabilization began, with mean eye velocities at 3.3°/s, 2.8°/s, and 4.7°/s for patients, relatives, and controls, respectively. Both the patients (p=0.01) and relatives (p=0.001) were significantly different from the controls. For 10°/s, group differences again emerged at 50 –100 ms, however only the patients (p=0.02), but not the relatives (p=0.08) were significantly different from the controls.
For the predictive pursuit gain, there was a significant main effect of group (F(2, 131) = 4.31, p=0.01) and velocity (F(1, 136) = 14.58, p=0.0002), but no significant velocity by group interaction (p=0.17) or effect of age (p=0.62). Schizophrenia patients (p= 0.01) and relatives (p= 0.05) had reduced gain compared to healthy controls (). The patients and relatives were not significant different (p=0.75). Again, the differences were more prominent at 18.7°/s (patients vs. controls, p=0.01; relatives vs. controls, p= 0.007) as compared to 10°/s (patients vs. controls, p=0.06; relatives vs. controls, p= 0.46). Removing age as a covariate did not change the significance levels.
Frequencies of saccades during the 1-second stabilized pursuit window were not statistically different (mean ± SD: 1.92±0.76, 2.04±0.71, 1.84±0.79 for patients, relatives, and controls, respectively, p>0.05).
Eye velocities during the twenty 50 ms-epochs were evaluated by means of PCA. It yielded two clearly separated principal components: an initial component consisting of the first 6 (equivalent to the first 300ms at 10.0°/s) or 2 (first 100ms at 18.7°/s) epochs and a second component consisting the subsequent epochs. These two latent components approximately correspond to the acceleration and steady state phases of the stabilized pursuit. Patients and relatives had significantly reduced eye velocity in both principal components at 18.7°/s, but not at 10.0°/s ().
Group comparisons of mean eye velocity (mean ± SD) during foveally stabilized pursuit among components derived from principle component analysis.
For maintenance pursuit gain, there was a significant main effect of group (F(2, 135) = 6.18, p=0.003) and velocity (p=0.04), but no significant effect of age (p=0.27) or group by velocity interaction (p=0.58). The patients had significant reduction in maintenance pursuit gain compared to the controls in 18.7°/s (p=0.04) but not 10.0°/s (p=0.06). The relatives did not differ from the controls in 10.0°/s (p=0.41) or 18.7°/s (p=0.20) (). Removing age as a covariate did not change the significance levels.
Test-retest a month apart in 10 schizophrenia patients suggested high reliabilities for predictive acceleration [ICC(95% CI): 0.82 (0.19–0.96), p=0.01, at 10.0 °/s and 0.81(0.14–0.96), p=0.02, at 18.7 °/s] and predictive pursuit gain [0.84 (0.34–0.96), p=0.006, at 10.0 °/s and 0.87(0.46–0.97), p=0.003, at 18.7 °/s]. The patients’ mean (+ SD) BPRS total scores were 33.6 ± 9.0, which were not correlated with pursuit measures in any target velocities (n=52, all p>0.1).