Age- and stereovision-dependent eye-hand coordination deficits in children with amblyopia and abnormal binocularity.

Purpose: To examine factors contributing to eye-hand coordination deficits in children with amblyopia and impaired stereovision.

Methods: Participants were 55 anisometropic or strabismic children aged 5.0 to 9.

Getting a grip: different actions and visual guidance of the thumb and finger in precision grasping.

We manipulated the visual information available for grasping to examine what is visually guided when subjects get a precision grip on a common class of object (upright cylinders). In Experiment 1, objects (2 sizes) were placed at different eccentricities to vary the relative proximity to the participant's (n = 6) body of their thumb and finger contact positions in the final grip orientations, with vision available throughout or only for movement programming. Thumb trajectories were straighter and less variable than finger paths, and the thumb normally made initial contact with the objects at a relatively invariant landing site, but consistent thumb first-contacts were disrupted without visual guidance.

Eye-hand coordination skills in children with and without amblyopia.

Purpose: To investigate whether binocular information provides benefits for programming and guidance of reach-to-grasp movements in normal children and whether these eye-hand coordination skills are impaired in children with amblyopia and abnormal binocularity.

Methods: Reach-to-grasp performance of the preferred hand in binocular versus monocular (dominant or nondominant eye occluded) conditions to different objects (two sizes, three locations, and two to three repetitions) was quantified by using a 3D motion-capture system. The participants were 36 children (age, 5-11 years) and 11 adults who were normally sighted and 21 children (age, 4-8 years) who had strabismus and/or anisometropia.

The Poggendorff illusion affects manual pointing as well as perceptual judgements.

Pointing movements made to a target defined by the imaginary intersection of a pointer with a distant landing line were examined in healthy human observers in order to determine whether such motor responses are susceptible to the Poggendorff effect. In this well-known geometric illusion observers make systematic extrapolation errors when the pointer abuts a second line (the inducer). The kinematics of extrapolation movements, in which no explicit target was present, where similar to those made in response to a rapid-onset (explicit) dot target.

Grasping deficits and adaptations in adults with stereo vision losses.

Purpose: To examine the effects of permanent versus brief reductions in binocular stereo vision on reaching and grasping (prehension) skills.

Methods: The first experiment compared prehension proficiency in 20 normal and 20 adults with long-term stereo-deficiency (10 with coarse and 10 with undetectable disparity sensitivities) when using binocular vision or just the dominant or nondominant eye. The second experiment examined effects of temporarily mimicking similar stereoacuity losses in normal adults, by placing defocusing low- or high-plus lenses over one eye, compared with their control (neutral lens) binocular performance.

Common cortical loci are activated during visuospatial interpolation and orientation discrimination judgements.

There is a wealth of literature on the role of short-range interactions between low-level orientation-tuned filters in the perception of discontinuous contours. However, little is known about how spatial information is integrated across more distant regions of the visual field in the absence of explicit local orientation cues, a process referred to here as visuospatial interpolation (VSI). To examine the neural correlates of VSI high field functional magnetic resonance imaging was used to study brain activity while observers either judged the alignment of three Gabor patches by a process of interpolation or discriminated the local orientation of the individual patches.

Biases and sensitivities in the Poggendorff effect when driven by subjective contours.

Purpose: A consensus in the existing literature suggests that the Poggendorff effect (a perceptual misalignment of two collinear transversal segments when separated by a pair of parallel contours) persists when the parallels are defined by Kanizsa-like subjective contours. However, previous studies have often been complicated by a lack of quantitative measures of effect size, statistical tests of significance, appropriate measures of baseline and control biases, or stringent definition of subjective contours. The aim of this study was thus to determine whether subjective contours are capable of driving the Poggendorff effect once other factors are accounted for.

Dissociation between vergence and binocular disparity cues in the control of prehension.

Binocular vision provides important advantages for controlling reach-to-grasp movements. We examined the possible source(s) of these advantages by comparing prehension proficiency under four different binocular viewing conditions, created by randomly placing a neutral lens (control), an eight dioptre prism (Base In or Base Out) or a low-power (2.00-3.

Prehension deficits in amblyopia.

Purpose: Visual defects associated with amblyopia have been extensively studied, but their impact on the performance of everyday visuomotor tasks is unclear. This study evaluates eye-hand coordination (prehension) skills in adult amblyopes compared with normal subjects.

Methods: Twenty amblyopes (10 strabismic, 10 nonstrabismic) with different degrees of visual acuity loss (mild, moderate, or severe) and stereodeficiency (reduced or undetectable) participated, along with 20 matched control subjects.

Advantages of binocular vision for the control of reaching and grasping.

Theoretical considerations suggest that binocular information should provide advantages, compared to monocular viewing, for the planning and execution of natural reaching and grasping actions, but empirical support for this is quite equivocal. We have examined these predictions on a simple prehension task in which normal subjects reached, grasped and lifted isolated cylindrical household objects (two sizes, four locations) in a well-lit environment, using binocular vision or with one eye occluded. Various kinematic measures reflecting the programming and on-line control of the movements were quantified, in combination with analyses of different types of error occurring in the velocity, spatial path and grip aperture profiles of each trial.

Scaling of letter size and contrast equalises perception across eccentricities and set sizes.

Double E(2)N(2) scaling, i.e. magnifying size and contrast, allows modelling of the deterioration of face recognition performance with increasing eccentricity (E) and the size (N) of the set from which a target face has to be identified.