Patent Abstract:
there is disclosed apparatus and method for a test of eye dominance of human subjects for which on each 10 - sec trial , one eye starts with a strong image that gets progressively weaker or does not get progressively stronger , while , at the same time , the other eye gets a weak image that gets progressively stronger . the initially strong image will always be seen at the beginning and eventually vision will flip to the other eye &# 39 ; s view once that image has achieved sufficient strength to overcome the dominance of the initially strong stimulus . the subject indicates recognition of the strengthening image and the time is recorded . results show that the test provides a reliable measure of eye dominance which is seen to vary considerably among people within a sample of normal adults .

Detailed Description:
as shown in fig1 and 2 , test stations 11 provided for access by a test subject 9 seated in chair 10 include a video monitor 13 connected to a personal computer 15 ( pc ) used as a control unit . also connected to pc 15 is a response pad 17 , serving as a subject response acceptor . receiving a control signal from pc 15 is a viewer 14 in the form of shutter glasses to be worn by subject 9 . interconnections between computer , glasses , and response pad may be wireless , or wired as shown . response pad 17 may have additional controls or may be replaced or augmented by a conventional computer keyboard . the fig2 embodiment is provided with an optional chin support 21 . in a preferred embodiment of the invention stimuli are presented in the center of a display on video monitor 13 ( 800 × 600 resolution ; 100 hz ) against a uniform background at mean luminance and viewed at a distance of about 80 - 90 cm ( optionally with a chin rest .) the masking display includes gray scale mondrian patterns used as a mask image that subtended 4 . 3 °× 4 . 3 ° and are preferably normalized to 60 percent contrast ( root mean square ). the target stimulus normally is an image of an arrow pointing either left or right (. preferably about 67 °× 1 . 33 °; 20 percent contrast , root mean square ). see fig5 . in an alternative embodiment , the target stimulus is a gray scale photograph of a female face ( 1 . 67 °× 1 . 17 °; 15 percent contrast , root mean square ) angled toward the left or the right . the location of the target stimulus may be jittered around the center coordinates of the masking display across trials to avoid fixation on one location . black and white circles ( 0 . 33 ° diameter ) frame the boundaries of the masking display in this embodiment . other embodiments may involve a mask or a blank display which does not reduce in contrast while the target is increasing in contrast . liquid crystal shutter glasses ( for example crystal eyes ; http :// reald - corporate . com ) are used to present the masking display and target stimulus dioptically . the presentation of the mask and the target may alternate with refreshes of the monitor . the opening and closing of the glass lenses allow the left and right eyes to view temporally alternate frames on the screen without flicker . thus , each eye may view one of the target or mask stimuli during a given trial . the eye viewing the dynamic mondrian mask or the target stimulus is randomized across trials . in another alternative embodiment , this masking display is replaced with a different display , preferably at mean luminance . all such procedures may be programmed in matlab version 7 . 6 , 2008a ( http :// www . mathworks . com /) and psychtoolbox version 3 ( http :// psychtoolbox . org or in other available protocols compatible with pc 15 . other methods and apparatus could be employed to present the two dissimilar images to left and right eyes within the scope of the invention . for example orthogonally polarized images could be presented to a subject wearing appropriately polarized goggles or glasses using projection or a half - silvered mirror to merge the images . although the parameters of the test procedure are flexible , one specific program provides that at the beginning of a trial , one eye views a full contrast mondrian mask pattern and the other eye views the target at 0 % contrast ( no stimulus ). during a trial , the target linearly increases in contrast at a rate of 1 % every 100 ms . at the same time the mondrian pattern of the masking display linearly decreases in contrast , preferably at the same rate as the target contrast increases . subjects are instructed to immediately indicate the direction in which the target stimulus was pointing ( left vs . right ) by pressing a corresponding one of two response keys . error feedback was not given . if subjects did not detect the target stimulus while the mondrian mask pattern was visible , the target remained on the screen at full contrast until a response was made . trials terminated once responses were made , and reaction time ( ri ) and accuracy were recorded . subjects performed 10 practice trials before moving on to an extended series of record trials ( either 100 trials or 50 trials , depending on time available ). record trials took on average six to seven minutes to complete . referring to fig5 , the left and middle columns represent the stimuli presented to each eye . during a trial , the contrast of the arrow increases and , at the same time , the contrast of the dynamic mondrian patterns decreases . the right column represents subjects &# 39 ; perception during the trial . subjects initially perceived the mondrian display and eventually the target stimulus ( in this case , the arrow ) breaks suppression . subjects respond as soon as they discriminate the direction of the target stimuli . to quantify the results of testing a subject , an eye dominance index may be derived by calculating the ratio of mean rts when the arrow was presented to the left eye ( lert ) relative to the mean right eye rts ( rert ). the stronger sensory eye would facilitate the breakage of suppression by the target stimulus and lead to shorter reaction times in the discrimination task . on the other hand , when the sensory dominant eye is presented with dynamic noise , it more strongly suppresses the target stimulus viewed by the other eye , which produces longer rts for identification of the direction in which the test stimulus was pointing . hence , this particular dominance index value greater than one indicates right eye sensory dominance and dominance index value less than one indicates left eye sensory dominance . alternative dominance indices could include a bert for when target and mask were presented to both eyes equally . such index value could be a numeral plus an indicator of r or l for the dominant eye . fig3 illustrates ( top line ) the time sequence for monitor target or mask display with the second and third lines indicating the two alternative viewer shutter openings of target or mask to left or right eye . the alternative controls produce lert and rert . in fig4 the top line is the same as fig3 , but lines 2 an 3 show two different sequences usable to obtain bert , i . e . response time in the same apparatus for subject viewing with both eyes for comparison with lert or rert . in addition to the variations and modifications to the apparatus and method described herein , numerous other variations will be apparent to those skilled in the art , and the scope of the invention extends to all such variations and modifications . we have devised and implemented a novel technique for quantifying the magnitude of interocular suppression as a means of measuring a given individual &# 39 ; s sensory dominant eye . it offers advantages over other ocular dominance tasks for several reasons . first , the task is objectively straightforward and easy for participants to understand and perform , as evidenced by near perfect accuracy evidenced in a sample subject set . with other suppression techniques , particularly those that employ binocular rivalry , states of perceptual uncertainty associated with transition states and mixed dominance create response uncertainty ; this uncertainty can be particularly problematic in that mixed dominance varies with stimulus features such as size and spatial frequency . with masking , mixed dominance rarely occurs , and the subject is not being asked to track rivalry but , instead , simply to indicate when the target emerging into dominance is sufficiently visible to report the direction in which it is pointing . second , our task can be completed in less than 10 min , unlike other tasks that require extended test trials to assess interocular suppression . third , the dominance measures derived here are reliable across time and with different stimulus targets . finally , this technique provides a variable distribution of scores and is sensitive enough to measure significant interocular differences within individuals . other studies have either failed to assess individual differences or have failed to find interocular differences . the present apparatus and method can reliably measure interocular suppression in cataract patients pre - and post - operatively , in order to better determine the relationship between suppression and monovision success as well satisfying other needs for reliable , reproducible measurement of interocular suppression . participants 88 observers ( 44 females ) were recruited from the vanderbilt university psychology department or through the vanderbilt university subject pool . 23 and 21 observers also participated in experiment 2 and 3 , respectively , in addition to experiment 1 . another 23 observers returned 1 day to 13 months later ( median = 8 months ) to repeat the experiment 1 in order to acquire test - retest reliability . participants ranged in age from 18 - 61 , with a mean age of 27 ( sd = 8 ). approximately 10 % were left handed . all participants provided written informed consent and , with the exception of 2 participants ( authors ), were naïve to the purpose of the study . far and near acuity values were measured using standardized tests provided by the bausch and lomb orthorator ( rochester , n . y .). both eyes were presented with a diamond square , which was delineated into quadrants representing the top , bottom , left and right of the diamond . a checkerboard pattern was presented to one or both eyes and observers were instructed to indicate the quadrant in which the pattern was located ( 4 - alternative - forced - choice ); for monocular testing , the untested eye viewed only the outline of the transparent quadrants . the size of the stimulus display was smaller for each subsequent trial , for a total of 9 stimulus displays . scores were based on the number of consecutive trials correctly answered ; they were collected dioptically and dichoptically , with and without participants &# 39 ; corrective lenses , and for far and near acuity , for a total 12 scores per observer . the preferred sighting eye was determined using the hole - in - the card test . a red cross ( 3 cm × 3 cm ) was presented approximately 5m in front of the observer . the observer held a card ( 13 cm × 20 cm ) with both hands , at arms length and moved the card until the cross was seen through hole in the center of the card ( 1 . 5 cm in diameter ), with both eyes open . then the observer was instructed to close one eye and report whether the cross remained in his / her line of view . the eye that allowed the observer to maintain the view of the cross while the other eye was closed was documented as the preferred sighting eye . stimuli were presented in the center of a video monitor ( 800 × 600 resolution ; 100 hz ) against a uniform background at mean luminance and viewed at a distance of 86 cm with a chin rest ( fig5 ). the cfs display ( 10 hz ) consisted of grayscale mondrian patterns that subtended 4 . 3 °× 4 . 3 ° and were normalized to 60 percent contrast ( root mean square ). in experiments 1 and 3 , the target stimulus was an image of an arrow pointing either left or right ( 0 . 67 °× 1 . 33 °; 20 percent contrast , root mean square ). in experiment 2 , the target stimulus was a grayscale photograph of a female face ( 1 . 67 °× 1 . 17 °; 15 percent contrast , root mean square ) angled toward the left or the right . the location of the target stimulus was jittered around the center coordinates of the cfs display across trials to avoid fixation on one location . black and white circles ( 0 . 33 ° diameter ) framed the boundaries of the cfs display at all times . liquid crystal shutter glasses ( crystaleyes ; http :// reald - corporate . com ) were used to present the cfs display and target stimulus dioptically . the presentation of the cfs and the target stimuli alternated with every refresh of the monitor . the asynchrony between the opening and closing of the glass lenses allowed the left and right eyes to view temporally alternate frames on the screen without any sensation of flicker . thus , each eye exclusively viewed one of the two stimuli during a given trial . the eyes viewing the dynamic mondrian and target stimulus were counterbalanced and randomized across trials . in the case of experiment 3 , the cfs display was replaced with a blank display at mean luminance . the experiment was programmed in matlab version 7 . 6 , 2008a ( http :// www . mathworks . com /) and psychtoolbox version 3 ( http :// psychtoolbox . org ). at the beginning of a trial , one eye viewed a full contrast mondrian pattern and the other eye viewed the target stimulus at 0 % contrast ( no stimulus ). during a trial , the target linearly increased in contrast at a rate of 1 % every 100 ms . at the same time the mondrian pattern comprising the cfs display linearly decreased in contrast at the same rate as the target contrast . observers were instructed to immediately indicate the direction in which the target stimulus was pointing ( left vs right ) by pressing one of two response keys . error feedback was not given . if observers did not detect the target stimulus while the mondrian pattern was visible , the target remained on the screen at full contrast until a response was made . trials terminated once responses were made , and reaction time ( ri ) and accuracy were recorded . observers performed 10 practice trials before moving on to an extended series of experimental trials ( either 100 trials or 50 trials , depending on experiment ). experiments 1 and 2 took on average , 6 - 7 minutes to complete . the design and task of experiment 3 were identical to that of experiment 1 with the exception that the cfs display was replaced with a blank screen fixed at mean luminance throughout the trial . the experiment took 2 minutes on average to complete . fig5 : experiment 1 paradigm . the left and middle columns represent the stimuli presented to each eye . during a trial , the contrast of the arrow increased and , at the same time , the contrast of the dynamic mondrian patterns decreased . the right column represents observers &# 39 ; perception during the trial . observers initially perceived the mondrian display and eventually the target stimulus ( in this case , the arrow ) broke suppression . observers responded as soon as they could discriminate the direction of the target stimulus . the principal results of the experiments are shown in fig6 , 7 , and 8 and are described below . participants in experiment 1 averaged at 98 percent correct accuracy . an eye dominance index was derived by calculating the ratio of mean rts when the arrow was presented to the left eye ( lert ) to the mean right eye rts ( rert ). the stronger sensory eye would facilitate the breakage of suppression by the target stimulus and lead to shorter reaction times in the discrimination task . in the same way , when the sensory dominant eye is presented with dynamic noise , it more strongly suppresses the target stimulus viewed by the other eye , which produces longer rts for identification of the direction in which the test stimulus was pointing . hence , dominance index values greater than one indicate right eye sensory dominance and dominance index values less than one indicate left eye sensory dominance . fig6 illustrates the group distribution of these eye dominance index values . the mean ratio between lert and rert was 1 . 02 , and the relatively small standard deviation associated with these index values , 0 . 18 , implies that sensory dominance was evenly distributed and relatively modest among our participants . still , a few individuals produced results indicative of extreme eye dominance , particularly for the left eye ( see inset to fig6 ). two were at least 3 standard deviations below the mean and their data were excluded in subsequent group analyses . values greater than 1 indicate right eye dominance and values below 1 indicate left eye dominance . the insert in the upper left corner plots separate histograms for lert ( red ) and rert ( blue ). the mean rt observed in experiment 1 was 6 . 85 s ( sd = 1 . 29 s ). across observers , there was a small but statistically significant difference in condition ( t ( 85 )= 2 . 21 , p = 0 . 03 ), such that participants were on average faster on trials where the arrow was presented to the right eye ( rert : m = 6 . 74 s , sd = 1 . 27 s ) than when it was presented to the left ( lert : m = 6 . 96 s , sd = i . 32 s ). indeed , the number of participants categorized as sensory right eye dominant ( 62 %) was significantly greater than the number of participants categorized as left eye dominant ( 38 %) based on the dominance index ( chi square = 4 . 65 , p = 0 . 03 ). a similar proportion of individuals ( 59 %) used their right eye as their preferred sighting eye , as measured with the hole - in - the - card test . however , differences in sighting dominance were not significant ( chi square = 3 . 05 , p & gt ; 0 . 05 ) and neither was the proportion of individuals with consistent sensory and sighting dominant eye significantly different from those who were inconsistent ( chi square = 0 . 429 , p & gt ; 0 . 05 ). apparently our measure of sensory eye dominance does not tap into the same processes as those involved in sighting dominance . we further examined whether individual differences in left eye and right eye suppression were associated with differences in acuity . however after correcting for multiple correlations , there was no significant relationship between any of the acuity scores and lert , rert or the dominance index . intra - individual interocular differences were also observed . 32 of 86 participants , i . e ., 37 % of those tested , showed significant differences between their lert and rert , based on sample t - tests . significant differences were also consistently found on the basis of non - overlapping 95 % confidence intervals ( fig3 ; suttle et al ., 2008 ). this suggests that our technique is sensitive enough to detect interocular differences within a large portion of our sample . fig7 : shows mean rts for left eye ( filled circles ) and right eye ( empty circles ) conditions for each participant . participants &# 39 ; data are ordered by their dominance index . error bars indicate 95 % confidence intervals . to determine the reliability of rt values across time , we conducted two separate control experiments . first , 12 observers performed 100 trials in which half of the time , the arrow was presented to one eye and the mondrian patterns to the other . this is twice the number of trials originally administered . we compared the mean lert and rert for the first and last 25 trials of each condition . although there was a main effect of block , which is the mean rt for the first 50 versus last 50 trials ( f ( 1 , 11 )= 7 . 45 ; mse = 0 . 269 ; p = 0 . 02 ), its interaction with condition was not significant ( f ( 1 , 11 )= 0 . 096 ; mse = 0 . 068 ; p & gt ; 0 . 05 ). similarly , the dominance index was not second , we examined test - retest reliability in 23 observers . there was a significant main effect of time ( f ( i , 22 )= 4 . 73 ; mse = 0 . 832 ; p = 0 . 04 ) but the interaction between time and mean rt for each condition was not significant ( f ( 1 , 22 )= 0 . 224 ; mse = 0 . 191 ; p & gt ; 0 . 05 ). furthermore , lert , rert , and dominance index was significantly correlated between and test and retest ( r = 0 . 69 , p & lt ; 0 . 001 ; r = 0 . 63 , p & lt ; 0 . 001 ; r = 0 . 61 ; p = 0 . 002 , respectively ). the large majority of observers maintained the same eye dominance on retest , as indicated ( these individuals correspond to data points in the upper left and lower right quadrants of fig8 , right ). only six individuals reversed their eye dominance index , and 5 of those 6 had very small index values to begin ( implying no significant eye dominance on this test ). among those observers with significant eye dominance , test - retest index values consistently implicated the same eye as the dominant eye . we also examined whether our results could be obtained using other , more naturalistic stimuli . in experiment 2 , the arrow was replaced with an image of a woman &# 39 ; s face angled towards the left or right . participants were significantly slower at responding to the angle of the face than the direction of the arrow ( f ( 1 , 22 )= 10 . 57 ; mse = 0 . 296 ; p = 0 . 004 ). however , there was no interaction between the type of stimulus and condition ( f ( 1 , 22 )= 1 . 3 ; mse =. i ; p & gt ; 0 . 05 ), which indicates the pattern of rts were similar across experiments . furthermore , a significant correlation existed between the dominance index values measured under the arrow and face conditions ( r = 0 . 74 , p & lt ; 0 . 001 ). hence , sensory eye dominance can be reliably measured with different stimuli using this interocular suppression technique . one may wonder whether we would obtain the same results without interocular suppression , that is , presenting the arrow monocularly without a competing stimulus . this would be analogous to the measurement of contrast sensitivity . in experiment 3 , the arrow ( increasing in contrast ) was viewed by one eye while a blank display was viewed by the other . participants performed the same task as in experiment 1 . we found no significant correlation between the dominance index obtained when participants performed the task with and without the cfs display . blake , r ., yang , y . & amp ; 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