Time Series Analysis of PRL Movement during Fixation

Previous studies of eccentric PRLs (preferred retinal loci) due to central scotoma have documented that the PRLs for fixation are significantly larger than foveal PRLs for fixation (e.g., (Schuchard and Raasch, 1992; Fletcher and Schuchard, 1995)). The fixation target can be found within a 9 degree or smaller retinal area for eccentric PRLs while foveal PRLs (i.e., normally functioning foveas) usually keep the fixation target within a 2 degree or smaller retinal area. These previous investigations of PRLs for fixation have studied the two dimensional spatial characteristics of monocular PRLs but not the dynamic temporal/spatial characteristics of the PRL during fixation. Therefore, it is not known whether the increased PRL size is due to larger drifts and/or microsaccades during fixation (although from this point on we will refer to the microsaccades as jerks since these small jumps can be quite large for some subjects).