Quantifying eye dominance strength – New insights into the neurophysiological bases of saccadic asymmetries

Distractor-induced saccade trajectory curvature reveals visual contralateral bias with respect to the dominant eye

The functional consequences of the visual system lateralization referred to as "eye dominance" remain poorly understood. We previously reported shorter hand reaction times for targets appearing in the contralateral visual hemifield with respect to the dominant eye (DE). Here, we further explore this contralateral bias by studying the influence of laterally placed visual distractors on vertical saccade trajectories, a sensitive method to assess visual processing. In binocular conditions, saccade trajectory curvature was larger toward a distractor placed in the contralateral hemifield with respect to the DE (e.g., in the left visual hemifield for a participant with a right dominant eye) than toward one presented in the ipsilateral hemifield (in the right visual hemifield in our example). When two distractors were present at the same time, the vertical saccade showed curvature toward the contralateral side. In monocular conditions, when one distractor was presented, a similar larger influence of the contralateral distractor was observed only when the viewing eye was the DE. When the non dominant eye (NDE) was viewing, curvature was symmetric for both distractor sides. Interestingly, this curvature was as large as the one obtained for the contralateral distractor when the DE was viewing, suggesting that eye dominance consequences rely on inhibition mechanisms present when the DE is viewing. Overall, these results demonstrate that DE influences visual integration occurring around saccade production and support a DE-based contralateral visual bias.

Dynamics of attentional and oculomotor orienting in visual foraging tasks

A vast amount of research has been carried out to understand how humans visually search for targets in their environment. However, this research has typically involved search for one unique target among several distractors. Although this line of research has yielded important insights into the basic characteristics of how humans explore their visual environment, this may not be a very realistic model for everyday visual orientation. Recently, researchers have used multi-target displays to assess orienting in the visual field. Eye movements in such tasks are, however, less well understood. Here, we investigated oculomotor dynamics during four visual foraging tasks differing in target crypticity (feature-based foraging vs. conjunction-based foraging) and the effector type being used for target selection (mouse foraging vs. gaze foraging). Our results show that both target crypticity and effector type affect foraging strategies. These changes are reflected in oculomotor dynamics, feature foraging being associated with focal exploration (long fixations and short-amplitude saccades), and conjunction foraging with ambient exploration (short fixations and high-amplitude saccades). These results provide important new information for existing accounts of visual attention and oculomotor control and emphasise the usefulness of foraging tasks for a better understanding of how humans orient in the visual environment.

Contrasting attentional biases in a saccadic choice task

To gain insight into how human observers select items in the visual field we pitted two attentional biases against one another in a single free choice design. The first bias is the nasal-temporal asymmetry during free choice tasks, where observers tend to choose targets that appear in their temporal hemifield over targets appearing in their nasal hemifield. The second is the choice bias found in studies of attentional priming. When observers have to select between a stimulus that shares features with a preceding target and a stimulus sharing features with previous distractors, they have a strong tendency to choose the preceding search target and this bias increases the more often the same search is repeated. Our results show that both biases affect saccadic choice, but they also show that the nasal-temporal bias can modulate the strength of the priming effects, but not vice versa. The priming effect was stronger for stimuli appearing in the temporal than in the nasal hemifield, but the nasal-temporal bias was similar for primed and unprimed targets. Additionally, our findings are the first to show how search repetition leads to faster saccades. The observed difference between the effects of the NTA and priming biases may reflect the difference in neural mechanisms thought to be behind these biases and that biases at lower levels may outrank higher-level biases, at least in their effect on visual attention.

Crossed versus conventional pseudophakic monovision for high myopic eyes: a prospective, randomized pilot study

Background

Aiming at spectacle independence, conventional pseudophakic monovision has been widely used in myopia patients with bilateral monofocal intraocular lens implantation. However, the crossed monovision, which is to correct the dominant eye for near vision and the non-dominant eye for distant vision, has been mentioned preferable for high myopic cataract patients by some studies.

We have conducted this study to compare clinical results to assess the feasibility of conventional and crossed monovision for high myopic pseudophakic patients by comparing patient satisfaction, visual function and spectacle independence.

Method

Forty-sixth high myopia patients were divided into two groups: 22 in crossed monovision group with patients whose refraction targeted to − 2.00 diopters (D) in the dominant eye and − 0.50D in the non-dominant eye; 24 in conventional monovision group with patients whose refraction targeted to − 0.50D in the dominant eye and − 2.00D in the non-dominant eye. Binocular uncorrected distance visual acuity (BUDVA), binocular uncorrected near visual acuity (BUNVA), binocular corrected distant visual acuity (BCDVA), binocular corrected near visual acuity (BCNVA), contrast visual acuity and stereoacuity were examined at postoperative 2 weeks, 1 month and 3 months. Questionnaires were completed by patients 3 months after binocular surgery to evaluate patients’ satisfaction and spectacle independence.

Results

The conventional monovision and the crossed monovision group showed no significant differences of mean BUDVA, BUNVA, BCDVA, BCNVA 2 weeks, 1 month or 3 months postoperatively (P > 0.05). There was no difference in the bilateral contrast sensitivity or stereoscopic function between the convention conventional and crossed monovision groups (P > 0.05). Patient satisfaction with near and distant vision, as well as spectacle dependence did not differ significantly between the two groups (P > 0.05).

Conclusion

Crossed pseudophakic monovision exhibited similar visual function when compared with conventional monovision technique, which indicates that it is an effective option to improve the visual functionality and quality of life for high myopic patients who considering bilateral cataract surgery.

Trial registration

The Institutional Review Board and Ethics committee of the First Affiliated Hospital of Chongqing Medical University, Chongqing, China. The trial registration was submitted in September 2018 and passed on March 18, 2020, and the registration number is: ChiCTR2000030935.

Saccade accuracy as an indicator of the competition between functional asymmetries in vision

Hemispheric specialization refers to the fact that cerebral hemispheres are not equivalent and that cognitive processes are lateralized in the brain. Although the potential links between handedness and the left hemisphere specialization for language have been widely studied, little attention has been paid to other motor preferences, such as eye dominance, that also are lateralized in the brain. For example, saccadic accuracy is higher in the hemifield contralateral to the dominant eye compared to the ipsilateral hemifield. Saccade accuracy is, however, also known to be sensitive to other functional asymmetries, such as the lateralization of visuo-spatial attention in the right hemisphere of the brain. Using a global effect paradigm in three different saccade latency ranges, we here propose to use saccade accuracy as an indicator of visual functional asymmetries. We show that for the shortest latencies, saccade accuracy is higher in the left than in the right visual hemifield, which could be due to the lateralization of visuo-spatial attention in the right hemisphere. For the longest latencies, however, saccade accuracy is higher toward the right than the left hemifield, probably due to the lateralization of local and global processing in the left and right hemispheres, respectively. These results could have a major impact on studies designed to measure the degree of lateralization of individuals. We here discuss both the theoretical and clinical contributions of these results.

Asymmetries of the visual system and their influence on visual performance and oculomotor dynamics

Our representation of the visual field is not homogenous. There are differences in resolution not only between the fovea and regions eccentric to it, but also between the nasal and temporal hemiretinae, that can be traced to asymmetric distributions of photoreceptors and ganglion cells. We review evidence for differences in visual and attentional processing and oculomotor behaviour that can be traced to asymmetries of the visual system, mainly emphasising nasal-temporal asymmetries. Asymmetries in the visual system manifest in various measures, in basic psychophysical tests of visual performance, attentional processing, choice behaviour, saccadic peak velocity, and latencies. Nasal-temporal asymmetries on saccadic latency seem primarily to occur for express saccades. Neural asymmetries between the upper and lower hemifields are strong and cause corresponding differences in performance between the hemifields. There are interesting individual differences in asymmetric processing which seem to be related to the strength of eye dominance. These neurophysiological asymmetries and the corresponding asymmetries in visual performance and oculomotor behaviour can strongly influence experimental results in vision and must be considered during experimental design and the interpretation of results.