Posts Tagged visual perception
[WEB SITE] High-power prismatic devices may further expand visual fields for patients with hemianopia – ScienceDaily
Series of novel optical designs may address some limitations of existing prism technology, which can expand visual fields by up to 30 degrees
Summary: Three new eyeglasses have now been designedusing high-power prisms to optimally expand the visual fields of patients with hemianopia, a condition in which the visual fields of both eyes are cut by half. The new designs address some limitations of existing prism correction available to this population.
Researchers from the Schepens Eye Research Institute of Massachusetts Eye and Ear and Harvard Medical School have designed three new eyeglasses using high-power prisms to optimally expand the visual fields of patients with hemianopia, a condition in which the visual fields of both eyes are cut by half. The new designs, described in Optometry and Vision Science, address some limitations of existing prism correction available to this population.
Impairing either the left or right halves of the visual fields in both eyes, hemianopia affects more than one million Americans and is most commonly caused by stroke, brain tumors and head trauma. Hemianopia reduces the natural visual field of about 180 degrees to a mere 90 degrees. People with hemianopia have difficulty detecting hazards on their blind sides, leading to collisions, falls and other accidents. Patients with hemianopia cannot legally drive in Massachusetts, where a visual field of 120 degrees is required.
One method of treatment for hemianopia is to expand the visual field with prisms mounted on or embedded in eyeglasses. A research team led by Eli Peli, M.Sc., O.D., FAAO, Professor of Ophthalmology at Harvard Medical School and the Moakley Scholar in Aging Eye Research at the Schepens Eye Research Institute of Mass. Eye and Ear, has been developing prism devices to expand the visual field for these patients for more than 15 years. Their most recent commercially available device introduced in 2013, the peripheral prism glasses, has been shown to expand the visual fields of patients with hemianopia by as much as 30 degrees, optically shifting objects from the blind side of the visual field to the seeing side.
With the goal of expanding the visual field on the blind side even farther, the researchers explored new optical techniques to create higher power image shifting devices designed to bend the light farther than the 30-degree limit of conventional prisms. In conventional prisms, increasing the angle eventually results in the light bending back into the prism, trapped by what is called “total internal reflection.”
“It’s not just that we need a device with a higher angle of light shifting to let them see farther,” said Dr. Peli (pictured right). “We also want the new devices to provide the additional range of vision when the patient scans their eyes in both directions. The current prism devices support such flexibility only when scanning into the seeing side.”
The authors introduced three new high-power prism concept devices in the Optometry and Vision Science paper:
Yoked Prisms in the Carrier Lens
By embedding the current prism in a spectacle lens that has prismatic power in the opposite direction, the image shifting effect is increased by the summation of the power of both prism types. This design allows for up to 36 degrees of expansion to the visual field on the patient’s blind side. This design permits 5 degrees of scanning range to the blind side with full effect.
Bi-Part Double Fresnel Prism
To increase the power of the peripheral prism, the bi-part double Fresnel prism combines two prism segments angled to each other. This design allows for up to 43 degrees of expansion to the visual field on the patient’s blind side and an increase to 14 degrees scanning range into the blind side.
Mirror-Based Periscopic Prism
The third approach — not yet fully manufactured — uses a pair of angled mirrors to deflect the image from the blind side to the seeing side — not unlike prism correction. Due to the mirror-based design, this device is distortion-free and does not suffer from the color splitting effect of prisms, which reduces image clarity. It may allow for up to 40 degrees of expansion to the visual field on the patient’s blind side with much wider scanning range permitted.
The researchers intend to fully design and implement the mirror-based periscopic prism and also begin testing all three designs in patients with hemianopia.
“The new optical devices can improve the functionality of the current prism devices used for visual field expansion and may find use in various other field expansion applications such as a mobility aid for patients with tunnel vision,” Dr. Peli said.
Materials provided by Massachusetts Eye and Ear Infirmary. Note: Content may be edited for style and length.
Eli Peli, Alex R. Bowers, Karen Keeney, Jae-Hyun Jung. High-Power Prismatic Devices for Oblique Peripheral Prisms. Optometry and Vision Science, 2016; 93 (5): 521 DOI: 10.1097/OPX.0000000000000820
via High-power prismatic devices may further expand visual fields for patients with hemianopia: Series of novel optical designs may address some limitations of existing prism technology, which can expand visual fields by up to 30 degrees — ScienceDaily
[ARTICLE] Using Virtual Reality to Transfer Motor Skill Knowledge from One Hand to Another – Full Text
As far as acquiring motor skills is concerned, training by voluntary physical movement is superior to all other forms of training (e.g. training by observation or passive movement of trainee’s hands by a robotic device). This obviously presents a major challenge in the rehabilitation of a paretic limb since voluntary control of physical movement is limited. Here, we describe a novel training scheme we have developed that has the potential to circumvent this major challenge. We exploited the voluntary control of one hand and provided real-time movement-based manipulated sensory feedback as if the other hand is moving. Visual manipulation through virtual reality (VR) was combined with a device that yokes left-hand fingers to passively follow right-hand voluntary finger movements. In healthy subjects, we demonstrate enhanced within-session performance gains of a limb in the absence of voluntary physical training. Results in healthy subjects suggest that training with the unique VR setup might also be beneficial for patients with upper limb hemiparesis by exploiting the voluntary control of their healthy hand to improve rehabilitation of their affected hand.
Physical practice is the most efficient form of training. Although this approach is well established1, it is very challenging in cases where the basic motor capability of the training hand is limited2. To bypass this problem, a large and growing body of literature examined various indirect approaches of motor training.
One such indirect training approach uses physical practice with one hand to introduce performance gains in the other (non-practiced) hand. This phenomenon, known as cross-education (CE) or intermanual transfer, has been studied extensively 3,4,5,6,7,8,9 and used to enhance performance in various motor tasks 10,11,12. For instance, in sport skill settings, studies have demonstrated that training basketball dribbling in one hand transfers to increased dribbling capabilities in the other, untrained hand 13,14,15.
In another indirect approach, motor learning is facilitated through the use of visual or sensory feedback. In learning by observation, it has been demonstrated that significant performance gains can be obtained simply by passively observing someone else perform the task16,17,18,19,20. Similarly, proprioceptive training, in which the limb is passively moved, was also shown to improve performance on motor tasks 12,21,22,23,24,25,26.
Together, these lines of research suggest that sensory input plays an important role in learning. Here, we demonstrate that manipulating online sensory feedback (visual and proprioceptive) during physical training of one limb results in augmented performance gain in the opposite limb. We describe a training regime that yields optimal performance outcome in a hand, in the absence of its voluntary physical training. The conceptual novelty of the proposed method resides in the fact that it combines the three different forms of learning – namely, learning by observation, CE, and passive movement. Here we examined whether the phenomenon of CE, together with mirrored visual feedback and passive movement, can be exploited to facilitate learning in healthy subjects in the absence of voluntary physical movement of the training limb.
The concept in this setup differs from direct attempts to physically train the hand. At the methodological level – we introduce a novel setup including advanced technologies such as 3D virtual reality, and custom built devices that allow manipulating visual and proprioceptive input in a natural environmental setting. Demonstrating improved outcome using the proposed training has key consequences for real-world learning. For example, children use sensory feedback in a manner that is different from that of adults27,28,29 and in order to optimize motor learning, children may require longer periods of practice. The use of CE together with manipulated sensory feedback might reduce training duration. Furthermore, acquisition of sport skills might be facilitated using this kind of sophisticated training. Finally, this can prove beneficial for the development of a new approach for rehabilitation of patients with unilateral motor deficits such as stroke.[…]
[Abstract] Avoiding unseen obstacles: Subcortical vision is not sufficient to maintain normal obstacle avoidance behaviour during reaching
Previous research found that a patient with cortical blindness (homonymous hemianopia) was able to successfully avoid an obstacle placed in his blind field, despite reporting no conscious awareness of it (Striemer, C. L., Chapman, C. S., & Goodale, M. A., 2009, PNAS, 106(37), 15996-16001). This finding led to the suggestion that dorsal stream areas, that are assumed to mediate obstacle avoidance behaviour, may obtain their visual input primarily from subcortical pathways. Hence, it was suggested that normal obstacle avoidance behaviour can proceed without input from the primary visual cortex. Here we tried to replicate this finding in a group of patients (N=6) that suffered from highly circumscribed lesions in the occipital lobe (including V1) that spared the subcortical structures that have been associated with action-blindsight. We also tested if obstacle avoidance behaviour differs depending on whether obstacles are placed only in the blind field or in both the blind and intact visual field of the patients simultaneously. As expected, all patients successfully avoided obstacles placed in their intact visual field. However, none of them showed reliable avoidance behaviour – as indicated by adjustments in the hand trajectory in response to obstacle position – for obstacles placed in their blind visual field. The effects were not dependent on whether one or two obstacles were present. These findings suggest that behaviour in complex visuomotor tasks relies on visual input from occipital areas.
Cognitive impairment, including deficits in memory, attention, visual perception, executive functioning, and self-awareness, is a common consequence of acquired brain injury (ABI). Subsequently, these cognitive impairments result in functional impairments in daily life activities for clients with ABI.
Rehabilitation efforts are categorized under two broad approaches: remediation and adaptation. Computer-assisted cognitive retraining (CACR) is a remediation approach using a computer platform to deliver cognitive exercises. CACR therapy can lead to improvements in memory and attention for adults with chronic ABI. However, memory and attention improvements from CACR may not carry over to functional improvements in occupational performance. Research suggested that therapy using an adaptive approach can yield functional improvements.
The purpose of this project was to design a systematic cognitive retraining curriculum, Bridge/Adapt, to bridge the gap between memory and attention-skill gains from CACR to functional improvements in occupational performance using adaptive strategies. The Bridge/Adapt curriculum incorporates the cognitive orientation of occupational performance (CO-OP) intervention approach, multicontext approach, and goal oriented attentional self-regulation training.
The curriculum includes eight modules that provide grading options so that occupational therapists can choose which difficulty level best suits the client. Clients practice adaptive strategies during simulations of instrumental activities of daily living (IADL), including financial management, appointment scheduling, and grocery shopping, utilizing the three themes in Bridge/Adapt: salience, context, and hierarchy. Clients use salience to choose meaningful goals to work on at home. Context refers to clients working on goals in varying environments. Lastly, clients work on tasks that increase in complexity with the hierarchical theme.