their extinction rate. bilateral stimuli were least extinguished when both stimuli were oriented horizontally, although both stimuli being oriented vertically also showed a reduction in extinguishing rate when compared to one stimulus vertical and one horizontal – in what could be assumed by the brain to represent two different surfaces. combining the brain bias towards facial processing and surface discovery, a follow-up study by dr. vuilleumier exposed subjects to paired visual stimuli in three phases. in the initial phase, stimuli were simply bilateral pairs, and extinction frequency was measured. in the next stage, the stimuli were surrounded with an oval, so that they appeared to represent eyes in a face. the extinction rate for this appearance was greatly reduced. finally, the patients were shown the stimuli minus the contextual oval – however, the reduced extinction rate persisted, as though the patients had learned to group these stimuli. the effect did not occur when the stimuli were surrounded by a nonoval shape, pointing towards facial processing as being the key to this phenomenon. visual feedback has also been studied in relation to visual extinction. patients were asked to touch a known target in a darkened room. a light attached to the patient's hand was sometimes briefly illuminated, to provide information about where the hand was in relation to the target. in some of these trials, a distracting light was also lit, which induced an extinction event in the patient. although the patient reported in such cases that he had not seen the indicator light on his hand, their performance was correspondingly better, similar to the results when visual feedback had been available. although the patient was not cognizant of having received the information, they were able to correctly act upon it, in a manner similar to blindsight. visual extinction has also been researched with regard to the effect of repetition on visual detection rate. patients were shown a colored (red or green) letter (o or e), one to each visual field, and then asked variably to report the color or shape of one letter or the other. extinction was found to be increased in the contralesional field when the patient was asked to report on a repeated characteristic – if both stimuli had been the same shape, or same color – regardless of whether the other characteristic had also been changed. this is another example of repetition blindness. future & research researchers conduct studies involving first-episode stroke patients. these patients typically have unilateral cerebral damage and/or contralateral extinction. current research is focusing on the more detailed role of the parietal lobe in visual extinction. the ability to understand which factors in visual processing determine whether a contralesional event, occurring on the half of the patient's brain or body opposing the site of a lesion, is observed or eliminated can provide crucial insights connecting to the mechanisms of attention and operation. routine eye examinations have begun to incorporate the knowledge of visual extinction. such examinations screen for simple, unsuspected visual field defects or abnormalities, while screening for the more severe extinction, by testing all quadrants of the visual field.