A contralateral preference in the lateral occipital area: sensory and attentional mechanisms.

Here we examined the level of the lateral occipital (LO) area within the processing stream of the ventral visual cortex. An important determinant of an area\u27s level of processing is whether it codes visual elements on both sides of the visual field, as do higher visual areas, or prefers those in the contralateral visual field, as do early visual areas. The former would suggest that LO, on one side, combines bilateral visual elements into a whole, while the latter suggests that it codes only the parts of forms. We showed that LO has a relative preference for visual objects in the contralateral visual field. LO responses were influenced by attention. However, relative changes in LO activity caused by changes in object location were preserved even when attention was shifted away from the objects to moving random dot patterns on the opposite side. Our data offer a new view on LO as an intermediate, but not a high-level, visual area in which neurons are driven by visual input and spatial attention in a multiplicative fashion

Human parietal reach region primarily encodes intrinsic visual direction, not extrinsic movement direction, in a visual motor dissociation task.

Posterior parietal cortex (PPC) participates in the planning of visuospatial behaviors, including reach movements, in gaze-centered coordinates. It is not known if these representations encode the visual goal in retinal coordinates, or the movement direction relative to gaze. Here, by dissociating the intrinsic retinal stimulus from the extrinsic direction of movement, we show that PPC employs a visual code. Using delayed pointing and event-related functional magnetic resonance imaging, we identified a cluster of PPC regions whose activity was topographically (contralaterally) related to the direction of the planned movement. We then switched the normal visual-motor spatial relationship by adapting subjects to optical left/right reversing prisms. With prisms, movement-related PPC topography reversed, remaining tied to the retinal image. Thus, remarkably, the PPC region in each hemisphere now responded more for planned ipsilateral pointing movements. Other non-PPC regions showed the opposite world- or motor-fixed pattern. These findings suggest that PPC primarily encodes not motor commands but movement goals in visual coordinates

Brief Communication Gaze-Centered Updating of Visual Space in Human Parietal Cortex

Single-unit recordings have identified a region in the posterior parietal cortex (PPC) of the monkey that represents and updates visual space in a gaze-centered frame. Here, using event-related functional magnetic resonance imaging, we identified an analogous bilateral region in the human PPC that shows contralateral topography for memory-guided eye movements and arm movements. Furthermore, when eye movements reversed the remembered horizontal target location relative to the gaze fixation point, this PPC region exchanged activity across the two cortical lobules. This shows that the human PPC dynamically updates the spatial goals for action in a gaze-centered frame

Full-field Chromatic Pupillometry for the Assessment of the Postillumination Pupil Response Driven by Melanopsin-Containing Retinal Ganglion Cells

Citation: Lei S, Goltz HC, Chandrakumar M, Wong AMF. Full-field chromatic pupillometry for the assessment of the postillumination pupil response driven by melanopsin-containing retinal ganglion cells. Invest Ophthalmol Vis Sci. 2014;55:4496-4503

Short-Term Saccadic Adaptation in Patients With Anisometropic Amblyopia

PURPOSE. Amblyopia is a developmental disorder characterized by impairment of spatiotemporal visual processing that also affects oculomotor and manual motor function. We investigated the effects of amblyopia on short-term visuomotor adaptation using a saccadic adaptation paradigm. METHODS. A total of 8 patients with anisometropic amblyopia and 11 visually-normal controls participated. Saccadic adaptation was induced using a double-step paradigm that displaced a saccadic visual target (at 6198) back toward central fixation by 4.28 during the ongoing saccade. Three test blocks, preadaptation, adaptation, and postadaptation, were performed sequentially while participants viewed binocularly and monocularly with the amblyopic and fellow eyes (nondominant and dominant eyes in controls) in three separate sessions. The spatial and temporal characteristics of saccadic adaptation were measured. RESULTS. Patients exhibited diminished saccadic gain adaptation. The percentage change in saccadic gain was lower in patients during amblyopic eye and binocular viewing compared to controls. Saccadic latencies were longer, and saccadic gains and latencies were more variable in patients during amblyopic eye viewing. The time constants of adaptation were comparable between controls and patients under all viewing conditions. CONCLUSIONS. The short-term adaptation of saccadic gain was weaker and more variable in patients during amblyopic eye and binocular viewing. Our findings suggest that visual error information necessary for adaptation is imprecise in amblyopia, leading to reduced modulation of saccadic gain, and support the proposal that the error signal driving saccadic adaptation is visual

The Effect of Sensory Uncertainty Due to Amblyopia (Lazy Eye) on the Planning and Execution of Visually-Guided 3D Reaching Movements

Background: Impairment of spatiotemporal visual processing in amblyopia has been studied extensively, but its effects on visuomotor tasks have rarely been examined. Here, we investigate how visual deficits in amblyopia affect motor planning and online control of visually-guided, unconstrained reaching movements. Methods: Thirteen patients with mild amblyopia, 13 with severe amblyopia and 13 visually-normal participants were recruited. Participants reached and touched a visual target during binocular and monocular viewing. Motor planning was assessed by examining spatial variability of the trajectory at 50–100 ms after movement onset. Online control was assessed by examining the endpoint variability and by calculating the coefficient of determination (R 2) which correlates the spatial position of the limb during the movement to endpoint position. Results: Patients with amblyopia had reduced precision of the motor plan in all viewing conditions as evidenced by increased variability of the reach early in the trajectory. Endpoint precision was comparable between patients with mild amblyopia and control participants. Patients with severe amblyopia had reduced endpoint precision along azimuth and elevation during amblyopic eye viewing only, and along the depth axis in all viewing conditions. In addition, they had significantly higher R 2 values at 70 % of movement time along the elevation and depth axes during amblyopic eye viewing. Conclusion: Sensory uncertainty due to amblyopia leads to reduced precision of the motor plan. The ability to implemen

Abnormal Integration of Audiovisual Spatial Information in Amblyopia (.pdf)

Perception of our environment involves combining information from multiple senses by a process termed multisensory integration. This process is evident in illusions like the McGurk effect, which juxtapose subtly incongruous auditory and visual stimuli to reveal the bias in the neurological networks underlying perception. Interestingly, studies using the McGurk effect show that patients with unilateral amblyopia integrate auditory and visual speech information in an abnormal way. It is unknown, however, whether this abnormality is specific to speech, or whether it reflects a more general failure of multisensory integration in amblyopia. To address this question, we used another illusion - the ventriloquism effect - to examine integration of non-speech audiovisual information. The ventriloquism effect is known to obey the maximum likelihood estimate (MLE) model of optimal combination in normal adults, and thus provides a predictive model to evaluate performance in amblyopia

Dataset of red light induced pupil constriction superimposed on post-illumination pupil response

We collected and analyzed pupil diameter data from of 7 visually normal participants to compare the maximum pupil constriction (MPC) induced by “Red Only” vs. “Blue+Red” visual stimulation conditions.The “Red Only” condition consisted of red light (640±10 nm) stimuli of variable intensity and duration presented to dark-adapted eyes with pupils at resting state. This condition stimulates the cone-driven activity of the intrinsically photosensitive retinal ganglion cells (ipRGC). The “Blue+Red” condition consisted of the same red light stimulus presented during ongoing blue (470±17 nm) light-induced post-illumination pupil response (PIPR), representing the cone-driven ipRGC activity superimposed on the melanopsin-driven intrinsic activity of the ipRGCs (“The Absence of Attenuating Effect of Red light Exposure on Pre-existing Melanopsin-Driven Post-illumination Pupil Response” Lei et al. (2016) [1]).MPC induced by the “Red Only” condition was compared with the MPC induced by the “Blue+Red” condition by multiple paired sample t-tests with Bonferroni correction. Keywords: Pupil light reflex, Chromatic pupillometry, Melanopsin, Post-illumination pupil respons

Test-Retest Reliability of Hemifield, Central-Field and Full-Field Chromatic Pupillometry for Assessing the Function of Melanopsin-Containing Retinal Ganglion Cells

"A sustained pupil constriction can be observed after the offset of a bright blue light stimulus. This post-illumination pupil response (PIPR) is produced by the intrinsically photosensitive melanopsin-containing retinal ganglion cells (ipRGCs), and can be measured by chromatic pupillometry. We previously described a clinically friendly chromatic pupillometry protocol that can induce PIPR with a brief blue light stimulus. The present study is to evaluate the test-retest reliability of current methods of inducing PIPR under hemifield, central-field and full-field stimulation conditions.