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. Author manuscript; available in PMC: 2014 Sep 1.
Published in final edited form as: Exp Eye Res. 2013 Apr 15;114:6–15. doi: 10.1016/j.exer.2013.04.001

Figure 2.

Figure 2

Schematic of the Sensory Prediction Error (SPE, magenta) concept. Whether considering the “normal” saccades (green) used in many studies of saccade adaptation induced by intrasaccadic target steps (ISSs, dark red), or the “part-way” saccades (blue) used by Bahcall & Kowler (2000), the resulting SPE is unchanged, despite a large difference in the retinal error (orange), thanks to offsetting by the sensory prediction (purple). Note that the SPE and the ISS are shown as identical in this example because: (1) the illustrated sensory prediction does not account for noise in the pre-saccade estimate of target eccentricity, and (2) the internal estimate of saccade amplitude (on which the sensory prediction must also rely) is illustrated as accounting for the saccadic execution noise, which it cannot. In actuality, the SPE would vary in magnitude relative to the ISS as a result of both noise sources.