Article
Four sensory processing tests that may help us better understand CVI
CVIer Grace details her trip to Dr. Merabet's lab at Harvard, including sensory processing tests that may help us better understand CVI.
I recently traveled to Boston to participate in a research study at the Laboratory for Visual Neuroplasticity at the Department of Ophthalmology at Massachusetts Eye & Ear and Harvard Medical School. Dr. Lotfi Merabet is the principal investigator, optometrist, and scientist who has dedicated a lot of his career to understanding cerebral/cortical visual impairment (CVI).
My parents have seen him present at many CVI conferences and mentioned that I could go to the lab and participate in activities that would add to the data Dr. Merabet and his team are gathering and studying.
Leading up to the trip, I felt excited but also unsure about what I would do and how tired it would make me. But no matter what, I wanted to contribute to the research. It’s important so that more people with CVI can be found and understood.
When my dad and I arrived at the lab, Dr. Merabet gave us a quick overview of the day and then asked me if I had any questions. One thing I wanted to understand was why he started his lab and what he is trying to learn.
Dr. Merabet explained, “We know that many people with CVI have difficulties finding things in their environment. We want to know if these search difficulties are vision-specific, or are they also generalized to other senses?”
We completed four tests that day. I also tried on the virtual reality headset and looked around the landscapes, which are typically part of the study, but my field of vision wouldn’t allow me to complete the activities. I also couldn’t participate in the eye-tracking activities due to my acuity.
How well do I use language?
1. The Wechsler test
The Wechsler test assesses language use. “The first activity is for what’s called verbal and nonverbal IQ, meaning, how well do you use language?” said Dr. Merabet. “It tells me a little bit about your ability to use language day-to-day.”
When given a word, I had to describe what it meant. I was asked to define a bunch of words. Some came easily and some did not. For example, there was one word I couldn’t remember but knew for sure I had heard in a favorite book, The War That Saved My Life by Kimberly Brubaker Bradley. So I listened to the book when I got home to try to figure out what it meant!
Then, I was given a pattern and choices to complete it. I had to figure out the best option. That one was fun because it was satisfying to complete the patterns.
Dr. Merabet told me that this test is informative because an eye test, like the one you’d do at the doctor’s, doesn’t tell you everything you need to know about how CVI affects a person, for example, how they are doing in school and how they use language. That’s why he uses this test to get a better idea of the person as a whole.
Is tactile search difficult for me, especially with larger areas?
2. The tactile search test
The tactile search test measures the ability to find objects by touch and without vision.
I had to look for a line segment that was oriented differently, using no vision, just the sense of touch. The line segments were covered by this plastic-feeling material, which was harder for me to feel. My strategy was to use my pointer, middle, and ring fingers on one hand because I think they are the best fingers for feeling details.
For me, this was more difficult than the Weschler test. I had to push a button when I found a line segment that was oriented differently and push a different button when the segment was not oriented differently. Sometimes I pushed the wrong button, the one I didn’t mean to push!
The researchers increased the difficulty level over time by making the arrays progressively larger. “We’re not only interested in whether you were able to find the different line segment,” said Dr. Merabet. “We’re also interested in figuring out what happens when we make it harder and harder to search.”
With this data, the team can evaluate a participant’s performance on the tactile search task, including how they handled the increasing difficulty. It didn’t get to a point where the search felt too difficult for me. It might have if they continued to increase the search area, but I don’t know.
Then we moved on to two activities that assessed my ability to integrate vision and hearing.
Does it help for me to use hearing and vision together?
3. The redundancy gain test
The redundancy gain test checks whether combining visual and auditory stimuli results in faster responses, indicating better information processing.
In this test, I had to respond when I saw a light or heard a sound. I’d also have to respond if I saw a light and heard a sound that happened at the same time. The lights were kind of far away for me to see, which was challenging. I didn’t know in what order the lights, sound, or both would occur, and switching between my senses super fast was fatiguing.
Dr. Merabet asked, “When you hear the sound and see the light together, are you faster? In other words, does one plus one make three? Typically the answer is yes. When you experience the sound and light together at the same time, you should get a bonus out of that.”
A few things made this test easier than the one that came next. There was only one light in the same place, so I didn’t have to scan for it. And when the light and sound occurred together, my brain was activated by whatever sense I had just used. For example, if I had just responded to a sound, my hearing was activated and my brain wanted to continue to use that sense. So, it didn’t feel like I was using my hearing and vision together, but I’d rely on the sense that I had just used.
Does my vision tell me where a sound is coming from?
4. The ventriloquism effect test
Lastly, the ventriloquism effect test explores how vision influences the perception of sound sources, suggesting vision tends to override hearing.
Dr. Merabet gave an example. “When you’re in a movie theater and you see somebody talking, you have the impression that the sound is coming out of their mouth, right? The reality isn’t the case. The speakers are actually all around the theater.”
This test setup consists of five lights with colored stickers and speakers underneath them. The participant responds by naming the color that corresponds to where the light and the sound came from at the same time.
I couldn’t see the stickers due to their distance. I knew there were colors there, but I didn’t know what they were. So we improvised, numbering the lights and speakers 1 through 5 from left to right. I responded with numbers instead of colors.
It wasn’t easy to be accurate with this task at all. I was trying to lean over the table to get as close as I could, but that made the sound location harder to identify because I was at that point where I couldn’t separate sounds from where they were coming from. Essentially, I could tell a little bit where the sounds were coming from, but it mostly sounded like they were from the same spot. I had to visually scan back and forth a lot to see the lights, which were spread in a row. This is hard for me because my best field of vision is limited to the periphery of my left eye.
CVI and the multi-sensory experience
These tests provide insights into multisensory information processing beyond traditional eye tests, which don’t capture the complete picture of what it is like to have CVI. I’m excited to see the results of the lab’s ongoing work.
I want people to understand CVI better because it is a common visual impairment. Studying how people with CVI use their senses has many applications. At school, I have trouble using my vision and hearing at the same time, so I need accommodations. I know I’ll continue to need these accommodations as an adult in the workplace too. But before I receive accommodations, the team or business has to understand why looking and listening is a struggle for me and allow for appropriate strategies to work around it. That’s just one of the many ways this research will inform society about people with CVI and their needs.
More about the Laboratory for Visual Neuroplasticity
Leader in the field of CVI and lab director, Lotfi B. Merabet, OD PhD MPH, leads the Laboratory for Visual Neuroplasticity in investigating how the brain develops and adapts to visual impairment due to brain based (i.e. CVI) and ocular based causes. They use advanced brain scanning to better understand how the brain is connected and responds to visual activities. They are looking for study participants aged 7 years older and diagnosed with CVI or ocular disease/injury to contribute to their research.
