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Neuropsychology examines the relationship between cognitive activity and corresponding cerebral conditions. At one end, psychophysics meticulously describes the details of behavior. At the other, physiology records brain cell activity during cognitive tasks. Bridging the two, neuropsychology establishes the neural correlate of behaviour when correlation methods are used, and extends to the critical neural substrate when a causal relationship can be established. Here we revisit the Hering-versus-Helmholtz controversy on binocular coordination from the psychophysician's description of combined saccade-vergence eye movements to the neurophysiological recording of motor and premotor neurons of the oculomotor neural circuitry. Whilst neo-Heringian psychophysicians and physiologists have accumulated arguments for separate saccade and vergence systems, at both the behavioral and the neural premotor levels, neo-Helmholtzians have also provided evidence for monocular programmed eye movements and commands at the premotor level. Bridging the two, we conclude that Hering and Helmholtz were both right. Importantly, the latter's viewpoint brings to the fore the importance of adaptive processes throughout life, in view of the neurobiological constraints emphasized by the former. [ABSTRACT FROM AUTHOR]

Citation information: Blythe HI, Holliman NS, Jainta S, Tbaily LW & Liversedge SP. Binocular coordination in response to two-dimensional, three-dimensional and stereoscopic visual stimuli. Ophthalmic Physiol Opt 2012, 32, 397-411. doi:10.1111/j.1475-1313.2012.00926.x Abstract Purpose: We were particularly interested in whether binocular coordination when viewing stereoscopic images would be more comparable to when viewing a 2D representation, or when viewing a real stimulus array in depth. Methods: Data are reported from an experiment examining binocular coordination in response to stereoscopically presented stimuli. Movements of both eyes were recorded as participants viewed LED stimuli in a real scene with depth, a 2D image of the scene, and a stereoscopic image of the scene. Results: When viewing real LEDs, vergence during saccades re-aligned the eyes in depth where necessary, with smaller adjustments during the following fixation. In contrast, when viewing the stereoscopic representation, vergence during saccades did not re-align the eyes in depth. The only effect of target depth on vergence occurred during the following fixation. Conclusions: We conclude that disparity in parafoveal objects, in isolation from other depth cues (and, minimally, conflicting with blur), was insufficient for the visual system to target saccades appropriately in depth. [ABSTRACT FROM AUTHOR]

Binocular yoking of saccades is essential for single vision of words during reading. This study examines the quality of binocular coordination in individuals with dyslexia, independent of the process of reading. Fifteen dyslexia children (11.2±1.4 years) and 15 non-dyslexia individuals (8 children, aged 11.1±1.3 years, and 7 adults, 24±3 years) were studied. Eye movements were recorded in two conditions. In the control condition, participants made saccades to a single target where the saccade direction and magnitude were controlled. In the experimental condition saccades were allowed to move freely while viewing paintings. The results indicated that, compared with the non-dyslexia group, the dyslexia group showed a larger saccade amplitude difference between the two eyes, as well as a larger conjugate post-saccadic drift, during painting exploration than that for saccades to a single target. While both groups showed a larger disconjugate post-saccadic drift during painting exploration relative to the control condition, this showed a negative correlation with saccade disconjugacy (i.e. disconjugate drift reduced the disparity) only for the non-dyslexia group. These results indicate that individuals with dyslexia have problems of binocular coordination, both during the saccade and fixations, which are independent of the reading process. It is suggested that this reflects an immaturity of the normal oculomotor learning mechanisms. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Stabilization of images on the fovea during either fore/aft translation of a subject or fore/aft movement of a visual target in front of a stationary observer imposes complex geometrical requirements that depend upon the eccentricity of the object of interest with respect to the eyes. Each eye needs to be rotated independently with varying proportions of conjugate (version) and disconjugate (vergence) eye movements to maintain fixation of the target. Here, we describe binocular coordination in the early response to translational movements of normal subjects along their naso-occipital axis. We recorded the responses evoked by small (about 4 cm), abrupt (about 0.7 g), fore/aft translations in four normal subjects while they viewed a near target. In the forward and backward starting positions the target was 15 or 10.5 cm away, respectively. Each subject was tested with the target centered between the eyes, aligned on the right eye, and placed to the right of the right eye by ∼3 cm. The three conditions differed only in the lateral eccentricity of the target, yet the geometrical requirements for image stabilization are very different: pure vergence, one eye still, or mostly version. We found that the eye-movement responses closely matched what was needed for visual stabilization of the target, though responses to stimuli calling for divergence were less accurate than those for convergence. The latency of these responses ranged from 40 to 65 ms and achieved about 80% of the ideal response by 90 to 100 ms after the onset of the stimulus. Next, we asked whether these eye movements were generated by the vestibular system or by high-level strategies for image stabilization, such as pursuit. Thus, in a second set of experiments we used the mean profile of fore\aft body motion computed for each subject to drive a small visual target across the same distances and in the same eccentricities used during body translations. We found that visually driven responses had longer latencies (by at least 80 ms, ranging from 144 to 155 ms) and slower dynamics (with significantly lower peak eye velocities), highlighting the different subsystems producing the two types of responses. Saccades were also an important component of the response to both visual and vestibular stimuli, less frequent during the centered- target configuration and more frequent during viewing of eccentric targets. Visual stimuli evoked saccadic corrections more often and at shorter latencies than did vestibular stimuli. Both smooth and saccadic eye movements were appropriately disconjugate and their pattern depended on whether the eyes were converging or diverging. [ABSTRACT FROM AUTHOR]