Monocular and binocular mechanisms mediating flicker adaptation
33.3011, Sunday, 17-May, 8:30 am - 12:30 pm, Banyan Breezeway
Xiaohua Zhuang1, Steven Shevell1,2,3; 1Institute for Mind and Biology, University of at Chicago, Chicago, USA, 2Department of Psychology, University of Chicago, Chicago, USA, 3Department of Ophthalmology & Visual Sciences, University of Chicago, Chicago, USA
Purpose: Is the loss of contrast sensitivity following exposure to flicker (flicker adaptation) mediated by a mechanism at a monocular level, binocular level or both? New experiments address this by exploiting the observation that flicker adaptation is stronger at higher than lower temporal frequencies. Methods and Results: Experiment I used 3Hz square-wave 50%-contrast flicker with an incremental pulse at 1/4 duty cycle (83-msec pulse in each 333-msec cycle). Binocular contrast sensitivity was measured following adaptation to in-phase flicker in both eyes or 180-degree out-of-phase flicker. At the binocular level, the flicker rate is 6Hz in the out-of-phase condition if the two eyes’ pulse trains sum up. This would cause stronger adaptation than binocular 3Hz flicker in the in-phase condition. However, similar sensitivity reduction was found in both phase conditions, as expected for independent monocular adapting mechanisms. Experiment II tested for interocular transfer of adaptation between eyes. Monocular left-eye contrast sensitivity was measured following adaption to (i) 10%-contrast flicker in only the left eye or (ii) 50%-contrast flicker in only the right eye. In addition, (iii) adaptation in both eyes simultaneously was tested with 10%-contrast flicker in the left eye and 50% in the right. Various phase differences between eyes were tested. Left-eye flicker (10%) alone caused the largest left-eye contrast-sensitivity reduction, though right-eye flicker (50%) alone caused some left-eye sensitivity loss. When presented in-phase, left-eye (10%) and right-eye (50%) flicker together resulted in similar left-eye sensitivity reduction as for right-eye flicker (50%) alone. Conclusion: Flicker adaptation was strongest when adapting and testing in only the same eye. Adaptation can be partially transferred interocularly with adaptation in only the opposite eye. Moreover, monocular adaptation was weakened when both eyes were adapted simultaneously at different contrasts. Thus flicker adaptation results from mechanisms at both the monocular and binocular levels.