Abstract
Abstract: :
Purpose: Stimulus motion smears an image on the retina. But a neural deblurring mechanism perceptually sharpens borders when they are in continuous motion while jittered borders are seen as blurred. In a different context, Thorn et al (1998) noted that optical blur has significantly less effect on the perceptual performance of myopes than of emmetropes. Therefore, we hypothesized that myopes may also be better able than emmetropes to perceptually overcome the smearing effect of continuous motion. Methods: 42 normal young adults participated; 27 were myopic and 15 were emmetropic. Three sets of parameters that show the greatest intersubject variation in a standard motion deblurring paradigm were used. Two horizontal bars consisting of a light gray and a dark gray side divided by a border in the center were presented sequentially on each trial. Each border was sharp or slightly blurred; one of the two borders always moved continuously or jittered while the other remained stable. Subjects reported which border appeared clearer or if both were equally clear. Each stimulus was presented briefly (133 ms) to avoid eye tracking and randomly left or right to avoid predictive eye movements. Results: The jittered border was seen as blurred relative to the stable border on more than 90% of the trials even if the stable border was slightly blurred. On average, the border in continuous motion was seen as equally clear to the stable border. Intersubject differences were very large. The difference between blur scores for continuous motion versus jitter ranged from 4% (no deblurring effect) to 83% (almost complete deblurring). Despite these large intersubject differences in motion deblurring, there was no significant difference between myopes and emmetropes. Myopes showed slightly less blur with jitter and slightly more blur with continuous motion but this interaction efffect was not significant (P = 0.127). Conclusions: The high amount of intersubject variability shown here suggests that deblurring may be the result of a higher order mechanism (beyond the striate cortex) as suggested by Burr and Morgan (1997). Motion deblurring was not significantly related to refractive error. Myopes are less affected by dioptric blur than emmetropes in other studies (i.e., Thorn et al, 1998) and were effected slightly less (not significantly) by jitter in this study. Contrary to our hypothesis, myopes showed a statistically insignificant weakness in their motion deblurring effect relative to emmetropes.
Keywords: myopia • adaptation: blur • motion–2D