Purchase this article with an account.
G. T. Timberlake, E. Omoscharka, S. A. Grose, J. H. Maino; The Role of PRL Visual Feedback in Maze Tracing. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3622.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
In manual tasks individuals with bilateral macular scotomas must use retinally eccentric Preferred Retinal Loci (PRL) for visual information to guide the hand. The PRL may scan an object, creating a visual spatial memory, and may provide continuous visual feedback of the object and hand. The extent of memory and feedback use is not known. Different PRL’s are sometimes used for different visual tasks, but it is unknown if this is true for manual tasks. We investigated these questions with the task of tracing a line pattern ("maze") with the index fingertip.
Seven subjects with bilateral macular scotomas from AMD traced mazes while viewing the maze and fingertip in an SLO (see image). Retinal positions of the PRL used to fixate (fPRL), fingertip, and maze, were measured from SLO images. There were three maze conditions: (1) continuously visible (Memory+Feedback) (2) presented for 10 sec of inspection, then removed before tracing (Memory), (3) presented in successive segments (Feedback). Tracing accuracy was calculated as the length the fingertip advanced on the maze divided by maze length. The retinal area for scanning the maze was determined from 3D dwell-time histograms of the maze on the retina showing the time a retinal area was occupied by the maze.
Mean tracing accuracies for Memory+Feedback (54.7%), Memory (15.7%), and Feedback (71.6%) were significantly different (p’s < 0.01). For Memory+Feedback mazes 3D dwell-time histograms showed that 80% of the retinal areas with highest percentage maze occupancy were on the fPRL; the remaining 20% were adjacent to the fPRL. For Feedback mazes the area of highest maze occupancy of each line segment as it was presented and traced was on the fPRL. For Memory mazes areas of highest maze occupancy were not on the fPRL and appeared random.
The finding that maze tracing accuracy is minimal with memory alone suggests that it is not spatial memory but visual feedback that provides information to guide the fingertip. With the finding that the retinal area of highest maze occupancy is the fPRL, we conclude that for maze tracing the fPRL provides visual feedback to guide the fingertip.
This PDF is available to Subscribers Only