Abstract
Purpose: :
To measure the effect of the correction of the natural ocular aberrations on the subject’s performance on three different visual tasks (subjective quality preference, familiar face recognition and facial expression recognition).
Methods: :
We used a custom-developed Adaptive-Optics (AO) system provided with an electromagnetic deformable mirror and a Hartmann-Shack wavefront sensor (Imagine Eyes, France) to measure and correct ocular high order aberrations. A psychophysics channel was inserted to present gray-scale images on a Mitsubishi Monitor. The system was controlled using custom routines written in Visual C++ and Matlab from two different computers, one controlling the AO system, the other a ViSaGe psychophysical platform (Cambridge Research System, UK). Computers were synchronized for a rapid presentation of visual stimuli under controlled aberrations (with the AO mirror) and best spherical refractive error correction (with a Badal system). Measurements were performed on 5 young subjects. After Visual Acuity (VA) had been measured with/without AO correction, experiments involving 3 visual tasks were performed: (1) Subjective quality preference: 34 natural images viewed alternatively and randomly through natural aberrations/AO correction. The subject’s task was to choose the "sharpest" one. (2) Familiar face recognition: 66 faces (30 familiar) were presented randomly with/without AO correction. The subject provided a graded response from 1-6. (3) Facial expression recognition with 61 different faces (happy and angry). Images subtended: 2.8º (1) and 1.4º (2,3). Results of quality preference were analyzed as percentage of images preferred with AO; Results of face (familiar and expression) recognition were analyzed as the area under Response Operating Curves ROC (Au_ROC).
Results: :
1) On average, subjects preferred 81±13 % of the images viewed under AO correction. There was a correlation between VA (which increased by x1.16±0.15 with AO correction) and % AO preference. 2) For familiar face recognition, Au_ROC increased on average by x1.07±0.05 with correction. 3) For facial expression recognition, Au_ROC increased by x1.02±0.03.
Conclusions: :
Correcting ocular aberrations produced an improvement in visual performance. While the subjective impression of sharpness increased significantly with AO correction, the improvement of familiar/ facial expression recognition was minor.
Keywords: aberrations • face perception • perception