Goro Maehara

A Game Platform for Treatment of Amblyopia

We have developed a prototype device for take-home use that can be used in the treatment of amblyopia. The therapeutic scenario we envision involves patients first visiting a clinic, where their vision parameters are assessed and suitable parameters are determined for therapy. Patients then proceed with the actual therapeutic treatment on their own, using our device, which consists of an Apple iPod Touch running a specially modified game application. Our rationale for choosing to develop the prototype around a game stems from multiple requirements that such an application satisfies. First, system operation must be sufficiently straight-forward that ease-of-use is not an obstacle. Second, the application itself should be compelling and motivate use more so than a traditional therapeutic task if it is to be used regularly outside of the clinic. This is particularly relevant for children, as compliance is a major issue for current treatments of childhood amblyopia. However, despite the traditional opinion that treatment of amblyopia is only effective in children, our initial results add to the growing body of evidence that improvements in visual function can be achieved in adults with amblyopia.

The Role of Suppression in Amblyopia

PURPOSE This study had three main goals: to assess the degree of suppression in patients with strabismic, anisometropic, and mixed amblyopia; to establish the relationship between suppression and the degree of amblyopia; and to compare the degree of suppression across the clinical subgroups within the sample. METHODS Using both standard measures of suppression (Bagolini lenses and neutral density [ND] filters, Worth 4-Dot test) and a new approach involving the measurement of dichoptic motion thresholds under conditions of variable interocular contrast, the degree of suppression in 43 amblyopic patients with strabismus, anisometropia, or a combination of both was quantified. RESULTS There was good agreement between the quantitative measures of suppression made with the new dichoptic motion threshold technique and measurements made with standard clinical techniques (Bagolini lenses and ND filters, Worth 4-Dot test). The degree of suppression was found to correlate directly with the degree of amblyopia within our clinical sample, whereby stronger suppression was associated with a greater difference in interocular acuity and poorer stereoacuity. Suppression was not related to the type or angle of strabismus when this was present or the previous treatment history. CONCLUSIONS These results suggest that suppression may have a primary role in the amblyopia syndrome and therefore have implications for the treatment of amblyopia.

A compact clinical instrument for quantifying suppression.

Purpose. We describe a compact and convenient clinical apparatus for the measurement of suppression based on a previously reported laboratory-based approach. In addition, we report and validate a novel, rapid psychophysical method for measuring suppression using this apparatus, which makes the technique more applicable to clinical practice. Methods. By using a Z800 dual pro head-mounted display driven by a MAC laptop, we provide dichoptic stimulation. Global motion stimuli composed of arrays of moving dots are presented to each eye. One set of dots move in a coherent direction (termed signal) whereas another set of dots move in a random direction (termed noise). To quantify performance, we measure the signal/noise ratio corresponding to a direction-discrimination threshold. Suppression is quantified by assessing the extent to which it matters which eye sees the signal and which eye sees the noise. Results. A space-saving, head-mounted display using current video technology offers an ideal solution for clinical practice. In addition, our optimized psychophysical method provided results that were in agreement with those produced using the original technique. We made measures of suppression on a group of nine adult amblyopic participants using this apparatus with both the original and new psychophysical paradigms. All participants had measurable suppression ranging from mild to severe. The two different psychophysical methods gave a strong correlation for the strength of suppression (rho = −0.83, p = 0.006). Conclusion. Combining the new apparatus and new psychophysical method creates a convenient and rapid technique for parametric measurement of interocular suppression. In addition, this apparatus constitutes the ideal platform for suppressors to combine information between their eyes in a similar way to binocularly normal people. This provides a convenient way for clinicians to implement the newly proposed binocular treatment of amblyopia that is based on antisuppression training.

Quantifying Sensory Eye Dominance in the Normal Visual System: A New Technique and Insights into Variation across Traditional Tests

PURPOSE Although eye dominance assessment is used to assist clinical decision-making, current understanding is limited by inconsistencies across the range of available tests. A new psychophysical test of sensory eye dominance has been developed that objectively measures the relative contribution of each eye to a fused suprathreshold binocular percept. METHODS Six standard tests and the newly developed test were used to measure motor and sensory dominance in a group of 44 binocularly normal individuals (mean age, 29.5 ± 9.10 years). The new test required observers to perform a motion coherence task under dichoptic viewing conditions, wherein a population of moving, luminance-defined signal (coherently moving) and noise (randomly moving) dots were presented separately to each eye. The observers judged the motion direction of the signal dots. Motion coherence thresholds were measured by varying the ratio of signal-to-noise dots, in a staircase procedure. RESULTS The new dichoptic motion coherence threshold test revealed a clear bimodal distribution of sensory eye dominance strength, wherein the majority of the participants (61%) showed weak dominance, but a significant minority (39%) showed strong dominance. Subsequent analysis revealed that the strong-dominance group showed greater consistency across the range of traditional eye dominance tests used. CONCLUSIONS This new quantitative dichoptic motion coherence threshold technique suggests that there are two separate sensory eye dominance strength distributions among observers with normal binocular vision: weak and strong eye dominance. This finding may provide a basis for clinical decision-making by indicating whether eye dominance is likely to be an important consideration in a particular patient.

The effects of flankers on contrast detection and discrimination in binocular, monocular, and dichoptic presentations

We investigated how two co-aligned adjacent stimuli (flankers) influence threshold versus pedestal contrast (TvC) functions in binocular, monocular, and dichoptic presentations. Targets were presented to the two eyes or to only one eye. Pedestals and flankers were presented to the same eye to which the target was presented (binocular or monocular presentations) or to the other eye (dichoptic presentation). In the binocular presentation of targets and pedestals, the binocular flankers lowered thresholds at low pedestal contrasts. The monocular flankers had a similar effect to the binocular flanker, although the threshold reduction was smaller. In the dichoptic presentation of a target and a pedestal, flankers lowered thresholds when flankers were presented to the eye where targets were presented. In contrast, dichoptic flankers elevated thresholds at intermediate pedestal contrasts when a pedestal was also dichoptically presented. We fitted binocular contrast gain control models to the data. It follows from the fitting results that flankers modulate outputs from spatial filters in the monocular processing stage of contrast gain control.

Importance of phase alignment for interocular suppression

We measured contrast thresholds for Gabor targets in the presence of maskers which had higher or lower spatial frequencies than the targets. A high-pass fractal masker elevated target contrast thresholds at low and intermediate pedestal contrasts in both monocular and dichoptic modes of presentation, suggesting that the masking occurs after a monocular processing stage. Moreover we found that a high-pass checkerboard masker elevated thresholds at the low and intermediate pedestal contrasts and that most of this threshold elevation disappeared when the phase of the maskers spatial components were scrambled. This masking was effective only in the dichoptic presentation, not in the monocular presentation. These results indicate that phase alignment of the high spatial frequency components plays a crucial role for interocular suppression. We speculate that phase alignments signal the existence of a luminance contour in the monocular image and that this signal suppresses processing of information in the other eye when there is no corresponding signal in that eye.

Pattern masking: The importance of remote spatial frequencies and their phase alignment

To assess the effects of spatial frequency and phase alignment of mask components in pattern masking, target threshold vs. mask contrast (TvC) functions for a sine-wave grating (S) target were measured for five types of mask: a sine-wave grating (S), a square-wave grating (Q), a missing fundamental square-wave grating (M), harmonic complexes consisting of phase-scrambled harmonics of a square wave (Qp), and harmonic complexes consisting of phase-scrambled harmonics of a missing fundamental square wave (Mp). Target and masks had the same fundamental frequency (0.46 cpd) and the target was added in phase with the fundamental frequency component of the mask. Under monocular viewing conditions, the strength of masking depends on phase relationships among mask spatial frequencies far removed from that of the target, at least 3 times the target frequency, only when there are common target and mask spatial frequencies. Under dichoptic viewing conditions, S and Q masks produced similar masking to each other and the phase-scrambled masks (Qp and Mp) produced less masking. The results suggest that pattern masking is spatial frequency broadband in nature and sensitive to the phase alignments of spatial components.

Perceptual learning in monocular pattern masking: experiments and explanations by the twin summation gain control model of contrast processing.

We investigated practice effects on contrast thresholds for target patterns. Results showed that practice decreased contrast thresholds when targets were presented on maskers. Thresholds tended to decrease more at the higher end of the masker contrast range. At least partially, learning transferred to stimuli of the untrained phase. We simulated changes in threshold versus contrast functions using a contrast-processing model and then fit the model to pre- and posttraining data. The simulation results and model fit suggest that learning in pattern masking can be accounted for by changes in nonlinear transducer functions for divisive inhibitory signals.

Does Cognitive Perception Have Access to Brief Temporal Events

To determine whether conscious perception has access to brief temporal event, we asked subjects in an odd-man out paradigm to determine which of the four Gaussian blobs was flickering asynchronously in time. We measure synchrony thresholds as a function of the base temporal frequency for spatially scaled stimuli in foveal and peripheral vision. The results are consistent with a time delay of around 67 milliseconds (ms) for foveal vision and 91 ms for peripheral vision. We conclude that conscious perception has access to only relatively long (∼ 67 ms) time events.

Spatial distortions produced by purely dichoptic-based visual motion

It is known that local, monocular motion (short-range motion) can produce local distortions of visual space. We wanted to know if local monocular motion was both sufficient and necessary for producing motion-based spatial distortions. We used a previously reported dichoptic motion stimulus in which the directional motion signal is not present in either eyes input but is only present after binocular combination. We show that such a stimulus can also induce perceived changes in spatial position. This suggests that local, monocular motion while being sufficient is not necessary for the production of motion-based illusions. It suggests that one source of motion signals responsible for this illusion is from binocular motion mechanisms.