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Makoto Miyakoshi, Scott Makeig, Andrew J Tatham, Felipe A Medeiros; A Novel Paradigm for Vision Functionometry in Glaucoma. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5646.
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© ARVO (1962-2015); The Authors (2016-present)
Although standard automated perimetry is traditionally used to assess visual function loss in conditions such as glaucoma, it may have a poor relationship to alterations in ability to perform activities of daily living. Here we describe a novel approach to vision functionometry -- investigating the active use of visual information in more complex visual environments. For this purpose, we developed an active visual search task in which subjects saccade freely across the screen to detect matching object pairs in an evolving display.
In the experiment, 4 sizes of Gabor patches with 4 possible different angles of stripes were presented to the screen (20 inch LCD monitor, 60 cm distance from the eyes) (Figure 1A). Five Gabor patches, positioned at random across the screen, were always visible on a gray background. Every 1.5 seconds, a new Gabor patch appeared while the oldest one disappeared. The subject’s task was to actively search for the infrequent (15% probability) occurrence of a pair of patches matching in size and orientation. The subject pressed a button whenever they identified a matching pair. There were 285 trials contained paired targets. Infrared eye-tracking data was obtained from left eye; 205-channel EEG data were recorded.
Overall response accuracy was 87% and mean reaction time was 959 ms (SD 321 ms). Smaller Gabor patches, and longer distances between the paired targets were associated with lower response accuracy and longer reaction times. Figure 1 shows an example of gaze trajectory when subject missed the target. EEG analysis using multivector autoregression on successful Hit trials revealed that information flow from primary visual cortex to right superior temporal gyrus decreases at 230ms, but it reverses direction and polarity at around 512ms (Figure 2). After mean reaction time, information flow increased from left parietal cortex to right prefrontal cortex.
We confirmed that target size and target pair distance controls subject’s performance, and the interaction between primary visual cortex and superior temporal cortex may correlate with active visual search behavior. Glaucoma patients compensating for either frank or incipient visual field loss may be expected to produce more saccades, shorter fixations, and/or altered fixation distribution , together with alterations in EEG activity associated with stimulus onsets and eye fixations.
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