Shifting attention

Thu, Jan 29 2015

The Effects of Prism Adaptation

Contributed by Cara Chong, Public Relations student

When Tristan Hynes began his undergraduate degree at the University of Alberta, he did not expect to end up in a psychology lab at MacEwan University. Yet, through a mixture of his interest in psychophysiology, the neurological aspects of psychology, and his background in stroke research, Tristan found himself applying for a research grant at MacEwan. The clinical applicability of the research also drew him in.

Tristan, with psychology faculty mentor, Dr. Chris Striemer, is exploring the effect of prism adaptation on leftward and rightward movements in healthy individuals. Patients who have damage to the right hemisphere of the brain—commonly, the parietal lobe—may suffer from neglect, a disorder in which their left side is unattended to spatially, physically and perceptually. As a result, patients also exhibit directional hypokinesia, initiating leftward movements much slower than rightward movements. Dr. Striemer is hoping to use prisms to reduce the time it takes for these patients to initiate leftward movements. Prism adaptation has also been used clinically to help patients attend to their neglected left side.

What is a prism?

Firstly, what is a prism? It is not a trick question. A prism is a transparent optical object that refracts light. Their ability to refract light is what makes prisms so useful when dealing with neglect. When two carefully angled prisms are used as lenses in goggles, they can be used to shift a patient’s attention. Two rightward shifting prisms used as lenses in a pair of goggles will make objects appear further to the right then they actually are. When the patient reaches for the object they initially miss far to the right; however, after a few more trials the patient will learn to adjust their movements leftward to compensate for the rightward visual shift. The leftward adjustment in response to the rightward prism shift has become a useful tool in retraining a patient’s attention to the left side.

What is prism adaptation?

“A stroke patient is neglecting their left side of space, so they don’t see what’s there,” explains Tristan. “What we’ll do is put the prisms on them, and shift their vision so they eventually learn to compensate.” Essentially, the prisms help improve the effects of the right hemisphere damage.

“When you take the prisms off, they’re still adapted,” says Tristan. A compensatory mechanism has been engaged where, because of the prisms, they’re better able to attend to their left-hand side. However, the longevity of the treatment is, as Tristan puts it, “not that great” with effects lasting from one hour to a few days, depending on the number of treatments.

Tristan will also examine if there is a magnitude effect. The prism lenses can vary in degree, so he will try to determine whether larger magnitudes of prism shift lead to larger effects than smaller magnitudes of prism shift. Previous research by Carley Borza, another student working in Dr. Striemer’s lab, demonstrated that prism adaptation speeded the initiation of movements in the direction opposite the prism shift. For example, leftward movements were faster after rightward shifting prisms and vice-versa. Based on Carley’s earlier work Tristan hypothesises that prisms that shift vision rightward will enhance the speed of leftward movements—and a larger degree in magnitude should further increase the speed of leftward movements.

Why use healthy individuals?

The data for the study will be collected from the MacEwan University student body, which will allow Tristan to compare the effect of prism adaptation on healthy individuals to those of stroke patients. The ultimate goal of the project is to understand how prisms influence attention and motor control so they can be used to treat patients with brain damage more effectively. “In the study of neglect, they’re pretty much indispensable because you can model a phenomenon like that in a normal person,” says Tristan.

“Prism adaptation is a volatile thing,” he elaborates. “Once you [a healthy individual] start feeling around and interacting with the world, your body readapts [to how it was].” With his research, Tristan hopes to isolate the motor mechanism to better understand prism adaptation and how prisms work. “If we know how they work, they can be better used in therapeutic applications.”

As it stands now, Tristan has gathered pilot data before launching the study. Moving forward, Tristan will begin collecting the data before launching into an analysis. Beyond that, he will be submitting applications for graduate studies and medical school—both are challenges he is ready to tackle.

Tristan is presenting his project as part of Student Research Week, and are also hoping to present their findings next year.

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