2020-05-15 at 14:00
Identification of the functional PRL for fine visual tasks
During fine visual tasks, eyes undergo complex fixational eye movements (FEM) comprised of drift and microsaccades. The peak of the distribution formed by the aggregate FEM is generally considered to be the preferred retinal locus (PRL). But, owing to the fact that vision is widely believed to be suppressed during microsaccades, the functional PRL (fPRL) may represent a smaller retinal region. Accurate identification of the fPRL is an important step in better understanding human foveal vision. We used high-speed, sub-arcmin, retinal-image-based eye tracking to measure the fPRL’s exact location and distribution. The system is an Adaptive Optics Scanning Laser Ophthalmoscope with stimulus projection capabilities combined with custom software for offline tracking and image analysis. We devised a Vernier hyperacuity task that engaged natural FEM while allowing acuity to be measured during brief stimulus exposures and over few cones of the retina. Three subjects reported offsets between two 2x1 arcmin horizontal black bars separated by 1 arcmin along 7 steps of 12 arcsec. Duration was 34ms. Each stimulus was presented monocularly within a small square in the center of four black fixation guides. Stimuli were presented in a predictable cadence every 2 seconds, which ensured constant fixation strategy during the experiment. Over 2000 trials with different offsets were presented in pseudorandom order for each subject. The conventional PRL was compared to the fPRL (determined from only those epochs of FEM when the stimulus was present). Preliminary results reveal a systematic tendency to recenter gaze within +/-3arcmin (+/-5 cones). The fPRL location is more confined and slightly deviated from the conventional PRL. Consistent with previous observations during a tumbling-E letter acuity task, microsaccade initiation and landing positions tended to form two distinct clusters, with the fPRL located somewhere in-between. More analysis will be presented to uncover the functional significance of the PRL. The presentation will also include more recent attempts to map visual acuity over the retina, in 2D. Finally, I will introduce a related study attempting to evaluate eye movement, its behavior and stability over various kind of targets and tasks. These works were conducted during my previous postdoc at UC Berkeley with Prof. Roorda and Banks.