A new interocular suppression technique for measuring sensory eye dominance

Abstract

Purpose: Recently devised tests have implemented forms of interocular suppression (e.g., binocular rivalry) to assess eye dominance. In an effort to combine the strengths of these tests, the authors introduce a new technique for quantifying the magnitude of interocular suppression by using an easily administered psychophysical test.

Methods: Eighty-eight observers participated in the interocular suppression test, which involved dichoptic presentation of dynamic noise to one eye and a target stimulus to the other. Observers made a form-discrimination judgment once the target emerged from suppression. The authors reasoned that the dominant eye is less susceptible to interocular suppression and as a result, perception and thus, form discrimination would be faster when the target is presented to the dominant eye as opposed to the nondominant eye. Observers' sighting dominance, acuity, contrast sensitivity, and test-retest reliability were also assessed.

Results: There were significant interocular differences in mean reaction times within and across observers. Of the observers, 68% and 32% observers were categorized as right eye dominant and left eye dominant, respectively, according to the test. Moreover, 38% of observers showed strong eye dominance. Observers' discrimination accuracy (98%) and test-retest reliability (r = 0.52-0.67) were high. Consistent with results in previous studies, statistical correlations were weak between the sighting dominance test, acuity scores, contrast sensitivity measures, and the interocular suppression test.

Conclusions: This interocular suppression technique offers an efficient, reliable, quantitative method of evaluating eye dominance and may be useful in making decisions about differential refractive correction of the two eyes.

Figure 1.

Experiment 1 paradigm: Left and middle columns: 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. Right column: observers' 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.

Figure 2.

The eye dominance index (ratio between leRT and reRT) in experiment 1. Values greater than 1 indicate right eye dominance and values below 1 indicate left eye dominance.

Figure 3.

Mean RTs for left eye (●) and right eye (○) conditions for each participant. Participants' data are ordered by their dominance index; values greater than 1 indicate right eye dominance and values less than 1 suggest left eye dominance. Error bars, 95% confidence intervals.

Figure 4.

Sensory dominance index values obtained from our interocular suppression technique during test and retest for 42 observers. Left: individuals' values at test and retest. Solid line: best-fit line from linear regression and can be compared with the dotted line, which is a perfect linear fit (r = 1). Right: a Bland-Altman plot in which differences between individuals' test and retest values are plotted against the mean of their test and retest values. Lines indicate the mean difference (solid line) and 2 SD from the mean difference or the 95% limits of agreement (dotted lines). *The outlier individual mentioned in the text.