Unreferenced spatial localization under monocular and dichoptic viewing conditions

Knowledge of eye position in the brain is critical for localization of objects in space. To investigate the accuracy and precision of eye position feedback in an unreferenced environment, subjects with normal ocular alignment attempted to localize briefly presented targets during monocular and dichoptic viewing. In the task, subjects’ used a computer mouse to position a response disk at the remembered location of the target. Under dichoptic viewing (with red (right eye)–green (left eye) glasses), target and response disks were presented to the same or alternate eyes, leading to four conditions [green target–green response cue (LL), green–red (LR), red–green (RL), and red–red (RR)]. Time interval between target and response disks was varied and localization errors were the difference between the estimated and real positions of the target disk. Overall, the precision of spatial localization (variance across trials) became progressively worse with time. Under dichoptic viewing, localization errors were significantly greater for alternate-eye trials as compared to same-eye trials and were correlated to the average phoria of each subject. Our data suggests that during binocular dissociation, spatial localization may be achieved by combining a reliable versional efference copy signal with a proprioceptive signal that is unreliable perhaps because it is from the wrong eye or is too noisy.

Unreferenced Spatial Localization Under Monocular and Dichoptic Viewing Conditions

Knowledge of eye position in the brain is critical for localization of objects in space. To investigate the accuracy and precision of eye position feedback in an unreferenced environment, subjects with normal ocular alignment attempted to localize briefly presented targets during monocular and dichoptic viewing. In the task, subjects’ used a computer mouse to position a response disk at the remembered location of the target. Under dichoptic viewing (with red (right eye) - green (left eye) glasses), target and response disks were presented to the same or alternate eyes, leading to four conditions [green target – green response cue (LL), green-red (LR), red-green (RL), and red-red (RR)]. Time interval between target and response disks was varied and localization errors were the difference between the estimated and real positions of the target disk. Overall, the precision of spatial localization (variance across trials) became progressively worse with time. Under dichoptic viewing, localization errors were significantly greater for alternate-eye trials as compared to same-eye trials and were correlated to the average phoria of each subject. We suggest that during these tasks, subjects are unable to compensate for their phoria, implying that oculomotor proprioception may not provide the required feedback of eye position.

Color scrambles reveal Red and Green half-axis mechanisms plus a Gray-tuned mechanism

In this paper we set up to enumerate and characterize mechanisms sensitive to color scrambles. A color scramble is a texture made of a finite number of elements drawn from a set Ω, in this case small colored squares, distributed according to a histogram. We use a novel method to derive a eight equiluminant lights along the Red-Green cardinal axis. We then generate a background annulus and a target disk to be detected in one of eight pre-defined locations. We modeled the mechanisms available to the subjects to do the task using the seed-expansion weighting procedure. This theory-free, data- driven approach, constrained only by the size of the set Ω, makes no assumptions about the number of mechanism used to perform the task, or about what they are sensitive to. We found that a model of three mechanisms explains well the data: one half-wave rectified mechanism sensitive to green, one half-wave rectified mechanism sensitive to red, and a mechanism sensitive to gray. We discuss the implications of this result.

Multiple states in visual working memory: Evidence from oculomotor capture by memory-matching distractors

Visual working memory (VWM) representations interact with attentional guidance, but there is controversy over whether multiple VWM items simultaneously influence attentional guidance. Extant studies relied on continuous variables like response times, which can obscure capture – especially if VWM representations cycle through interactive and non-interactive states. We employed an oculomotor paradigm to characterize discrete attentional capture events under both high and low VWM load. Participants held one or two colors in memory, then executed a saccade to a target disk. On some trials, a distractor (sometimes VWM-matching) appeared simultaneous with the target. Eye movements were more frequently directed to a VWM-matching than a non-matching distractor for both load conditions. However, oculomotor capture by a VWM-matching distractor occurred less frequently (by approximately half) under high compared with low load. These results suggest that, without task demands to maintain both, one VWM item is held in an active state at a time.

Feasibility of Navigable Percutaneous Disk Decompressor (L'DISQ-C) for Cervical Disk Herniation

Objective To assess the procedural efficacy and safety of a Navigable Percutaneous Disk Decompressor (L'DISQ-C) for cervical disk herniation. Methods We performed intradiskal decompression on cervical spine specimens from five human cadavers using the L'DISQ-C under C-arm fluoroscopic guidance. We evaluated our success for positioning the navigable wand tip into the target region and recorded temperature variation at various distances from the wand tip in the cervical nucleus pulposus. The histologic effect of plasma decompression was examined microscopically using harvested tissues adjacent to the procedure site. Results We successfully navigated the tip of the L'DISQ-C into the target region of the posterior cervical disks on the first insertion attempt in all C3–C4 to C6–C7 disks and in 50% of the C2–C3 and C7–T1 disks. The average temperature elevations within the nucleus pulposus ranged from 4.14 ± 0.08°C to 12.17 ± 0.76°C at various distances from the wand tip with or without saline infusion. A histologic examination showed only minor denaturation at the marginal border of the procedure tract. Conclusion We effectively navigated the L'DISQ-C wand tip into the posterior target region of six cadaveric cervical disks and performed percutaneous resection of the target disk tissues without significant thermal or structural damage to adjacent tissues.

The Development of End-State Comfort Planning in Preschool Children

We investigated the development of the end-state comfort effect in young children. Fifty-one children from three age-groups (3, 4, and 5 years old) participated in the study. They performed the dowel placing task, which required them to reach for a horizontal dowel and to insert one of its ends into a target disk. Depending on which end was instructed, end-state comfort could be reached by picking up the dowel either with an overhand or with an underhand grip. All children reached for the dowel with an overhand grasp when this resulted in a comfortable end-state (i.e., thumb-up posture). A different pattern emerged when an underhand grip had to be selected. Here, 18% of the 3-year-olds, 45% of the 4-year-olds, and 67% of the 5-year-olds used an underhand grip and finished the action comfortably. For the first time, these results show a distinct pattern of gradual improvement in children’s sensitivity to reach end-state comfort across three age-groups.

Time-locked Perceptual Fading Induced by Visual Transients

After prolonged fixation, a stationary object placed in the peripheral visual field fades and disappears from our visual awareness, especially at low luminance contrast (the Troxler effect). Here, we report that similar fading can be triggered by visual transients, such as additional visual stimuli flashed near the object, apparent motion, or a brief removal of the object itself (blinking). The fading occurs even without prolonged adaptation and is time-locked to the presentation of the visual transients. Experiments show that the effect of a flashed object decreased monotonically as a function of the distance from the target object. Consistent with this result, when apparent motion, consisting of a sequence of flashes was presented between stationary disks, these target disks perceptually disappeared as if erased by the moving object. Blinking the target disk, instead of flashing an additional visual object, turned out to be sufficient to induce the fading. The effect of blinking peaked around a blink duration of 80 msec. Our findings reveal a unique mechanism that controls the visibility of visual objects in a spatially selective and time-locked manner in response to transient visual inputs. Possible mechanisms underlying this phenomenon will be discussed.