Meridional Attentional Asymmetries in Astigmatic Eyes

Abstract

Purpose: To investigate the impact of attention orientation in young myopic adults with astigmatism.

Methods: The effect of attention on foveal meridional performance and anisotropy was measured in corrected myopes with various levels of astigmatism (with-the-rule astigmatism ≤ -0.75D, Axis: 180 ± 20) using orientation-based attention. Attention was manipulated by instructing subjects to attend to either the horizontal or the vertical line of a central pre-stimulus (a pulsed cross) along separate blocks of trials. For each attention condition, meridional acuity and reaction times were measured via an annulus Gabor target situated remotely from the cross and presented at random horizontally and vertically in a two-alternative forced-choice employing two interleaved staircase procedures (one-up/one-down). Attention modulations were estimated by the difference in performance between horizontal and vertical attention.

Results: Foveal meridional performance and anisotropy were strongly affected by the orientation of attention, which appeared critical for the enhancement of reaction times and resolution. Under congruent orienting of attention, foveal meridional anisotropy was correlated with the amount of defocus for both reaction time and resolution, demonstrating greater vertical performance than horizontal performance as myopia increased. Compatible with an attentional compensation of blur through optimal orienting of attention, vertical attention enhanced reaction times compared to horizontal attention and was accompanied by an increase in overall acuity when myopia increased. Increased astigmatism was associated with smaller attention effects and asymmetry, suggesting potential deficits in the compensation of blur in astigmatic eyes.

Conclusion: Collectively, attention to orientation plays a significant role in horizontal-vertical foveal meridional anisotropy and can modulate the asymmetry of foveal perception imposed by the optics of the eye in episodes of uncorrected vision. Further work is necessary to understand how attention and refractive errors interact during visual development. These results may have practical implications for methods to enhance vision with attention training in myopic astigmats.

Keywords: astigmatism; attention; meridional anisotropy; myopia; visual performance.

Figure 1

The temporal structure of the study. The sequence of the stimulation started with the presentation of a high contrast pulsed cross adaptor, used to direct the attention of the subject along the vertical or the horizontal at the beginning of the test and just before the presentation of the visual target. The visual target, an annulus Gabor either vertical (V) or horizontal (H), is used to determine resolution acuity under the meridional attention manipulation.

Figure 2

Adaptor effect. Effect of the adaptor on horizontal (H) and vertical (V) resolution acuity for each subject. In all the figures, the error bar corresponds to the standard error.

Figure 3

Foveal meridional anisotropy (fVHA) of performance. (fVHA) when congruently attending to the orientation of targets as a function of the amount of sphere for (A) resolution acuity and (B) RTs. As the amount of defocus increased, a relative increase in vertical performance was observed as compared to the horizontal.

Figure 4

Effect of attention congruency on (fVHA). (A) Attention-related modulation of meridional asymmetry for RTs and acuity in subjects with sphere <−2.50D. (B) Attention-related modulation of meridional asymmetry in acuity as a function of sphere. *P < 0.05.

Figure 5

Congruency-related attentional modulation of RTs. Change in RTs was associated with switching attention from the congruent to the incongruent meridian for horizontal, vertical or both target orientations. The grey dots indicate the individual attention effect on RT values for each target meridian; the red bars indicate the mean value; the shaded areas represent one standard error. *P < 0.05, ns not significant.

Figure 6

Congruency-related attentional modulation of resolution acuity. (A) Change in resolution acuity associated with switching attention from the congruent to the incongruent meridian for horizontal to vertical. (B) Magnitude of the congruence-related attention modulation as a function of astigmatism.

Figure 7

Meridional asymmetry of congruence-related attention. (A) Attention-related modulation of meridional asymmetry for RTs and acuity in subjects with sphere <−2.50D. (B) Attention-related modulation of meridional asymmetry in acuity as a function of sphere. *P < 0.05, ns not significant.

Figure 8

Orientation-related attentional modulations. (A) Attention-related modulation of meridional asymmetry for RTs and acuity in subject with sphere <−2.50D. (B) Orientation-related attentional modulations in overall acuity as a function of defocus. *P < 0.05, ns not significant.

Figure 9

Meridional difference in orientation-related attentional modulations. (A) Orientation-related attentional modulations of vertical and horizontal acuity. (B) Magnitude of the difference in the orientation-related attentional modulations as a function of astigmatism. The arrows indicate the acuity changes in orientation-related attentional modulations between meridians.