Figure 2.

Behavioral OKR measurements at 5 dpf. Smooth pursuit eye velocity at 11 different spatial frequencies of the stimulation between 0.04 and 0.2 cpd was measured at a constant angular velocity of 7.5 degrees per second. The value obtained at 0.2 cpd was set as the zero value. For statistical analysis, the significance between each data point and the velocity at 0.2 cpd was calculated. Statistical analysis reveals highly significant differences between the data points of 0.04 and 0.15 cpd compared to 0.2 cpd (p < 0.001). At 0.16 cpd (p = 0.0055) the optokinetic response is still elicited, whereas at 0.17 cpd (p = 0.1557) the values do not differ significantly anymore. 0.16 cpd represents the finest grating the eye still can resolve, which is equal to the cut-off frequency or the visual acuity of the fish.