Changes in Phoria and Convergence Peak Velocity Figure 7. Summary of average peak velocities (6/s) with one standard deviation of all 46 convergence step responses after near 16u sustained fixation (top) and after far 16 sustained fixation (bottom). Far step data after sustained fixation of 16u (black), near step data after sustained fixation of 16u (light gray), far step data after sustained fixation of 1u (dark gray) and near step data after sustained fixation of 1u (white) are plotted. The number of samples is reported below the plotted data. When the phoria is maintained at one position, convergence responses with a 1u initial vergence position are faster than responses with a 12u initial vergence position. doi:10.1371/journal.pone.0020883.g007 but was moderately correlated for near steps. The near steps were collected at the beginning of the experiment so it is unlikely that fatigue was a confounding variable that led to a reduction in correlation for the near steps compared to the far steps analysis. However, the results support that the change in phoria was moderately correlated for near steps. Figure 8. Linear regression plot of the change in convergence peak velocity (6/s) of the near steps (solid triangle) and of the far steps (open circles) as a function of the change in phoria level (D). The change in phoria level is defined as phoria after near [far] steps during the near sustained fixation task minus phoria after near [far] steps during the far sustained fixation task. Positive phoria changes refer to an esophoric shift in phoria. Similarly, the change in peak velocity is defined as the peak velocity of steps after the near sustained fixation task minus the peak velocity of steps after the far sustained task. Positive peak velocity changes refer to faster convergence peak velocity values during 16u (near) sustained fixation task compared to the 1u (far) sustained fixation task. doi:10.1371/journal.pone.0020883.g008 PLoS ONE | www.plosone.org 9 June 2011 | Volume 6 | Issue 6 | e20883