Two years ago, I attended a special art exhibition about sensory loss at the Weisman Art Museum, hosted by the Center for Applied and Translational Sensory Science (CATSS) in the University of Minnesota. The audiences were intentionally separated into small groups such that each group had members with vision loss, hearing loss, dual sensory loss, or intact vision and hearing. Although visiting museums is usually easy, relaxing, and even personal, it was quite different this time. It was a challenge to ensure that every group member was enjoying the art. We tried everything we could think of — sign language, writing, voice-to-text app etc., but still felt a little bit helpless when standing in front of an abstract art. At the end of the tour, the host invited us to sit in a circle and chat about our experience and feelings. It was then I heard the perspective that people with sensory loss should not be regarded as disabled, they are just different as part of human diversity.
Sensory impairment is part of human diversity. This was a new perspective for me but made so much sense. Although it was initially introduced to me from a society or humanity point of view, in the past two years I have frequently revisited this idea from research, rehabilitation, or science point of view. The more I know about this field, the more I realize that our “being” is an interaction between individual and environment, with strategies as a mediate factor. No matter where we are on the spectrum of sensory quality, we share common strategies for being.
Vision and hearing are spectrum
Like many other researchers, in my manuscripts I often write “all participants have normal or corrected to normal vision”, or “normal hearing was confirmed by audiograms”. On one hand, I often question that the criteria for normal vision and normal hearing are too arbitrary: why a visual acuity of 20/40 is normal but 20/45 is not? Why only some sound frequencies on the audiogram are included in the calculation of hearing threshold, but others are not? On the other hand, however, I do need some “cut-off” values to set the inclusion criteria for my studies. Similarly, DMV need some “cut-off” values to decide whether people can still drive, and insurance companies need some “cut-off” values to decide which medical expenses they will cover.
However, from normal vision to no vision, and from normal hearing to no hearing, are indeed broad spectrum, just like running — some people are fast, some people are slow, and the majority of people are in the middle. We are individual points along the spectrum, and our positions are susceptible to many factors, such as lighting, weather, environment , and of course age and diseases.
We all have “visual field loss”
Recently I have been reading and thinking a lot about space perception. Imagine that you have just moved to a new office building. You have to learn a new route from home to the building, learn the layout of your floor (at least know how to get to the bathroom), and overtime you might even be able to remember every single decoration on the walls of the hallway. While previous studies have looked into every single step of this spatial learning process, very little is known about how visual loss affect our perception of space.
Skipping all the technical jargon, I just want to share this new perspective I have about visual field. Try looking straight ahead and keep your eye steady, how much of the room can you see? Now keep you head still and freely roll your eyes, how much more of the room can you see? Now keep your body still and freely turn your head, how much more of the room can you see? Lastly, when you freely walk around, how much more of the room can you see? My point is that even with “normal vision”, we don’t have a full vision. We have to use strategies such as eye, head, and body movements to make up for our limited visual field. Such strategies are exactly the same as those used by people with visual field loss due to eye pathologies*. How much of the findings about spatial perception in “normal vision” can generalize to “visual field loss”? I will let you know when I find the answer.
Sensory compensation is common for all of us
In the research field about sensory loss, we often talk about sensory compensation. The idea is that we can, and we should, utilize our other sense to compensate for the impaired one. A well known example is that some people who are blind can produce clicking sound by their tongue or fingers, and then use the echoes of the clicking sound to find the openings of a hallway, or their distance from a wall. Learning to use hearing is indeed a critical part of the orientation and mobility training for blind or visually impaired individuals. For example, when crossing a street, many of us who have normal vision (and follow traffic rules) would simply wait until the pedestrian walking turn green to start crossing, while people who are blind or visually impaired need to listen carefully to the parallel and perpendicular traffic and analyze: How fast are the cars? How long does it take for them to reach the intersection? How much time do I have to cross street? How can I cross the street without veering out of the crosswalk…
You might think that such sensory compensation is awesome and definitely “unordinary”. But have you ever sneaked home after curfew, or gone to the bathroom in the dark at the middle of the night? You cautiously listen to every step and reach out to everything adjacent to you. You might be able to notice the different ambient sound in the living room and hallway, and the obvious echoes in the bathroom. We all encounter such moments with not useful or unreliable sense, when we use sensory compensation strategy intuitively. In the case of sensory loss, there are much more such moments, therefore people with sensory loss use sensory compensation more frequently.
Cracking a case is just a matter of gathering evidence
Imagine that a cat is meowing at you somewhere (if you need help with imagining a cat please go to my fun staff page), how well can you determine the distance of the cat from you?
If you know the average size of a normal sized cat, you might be able to estimate the distance by how big the cat looks like from that distance.
If it is a familiar cat that you know the volume of its meowing, you might be able to estimate the distance by the volume of the cat from that distance.
If it is a room that you know its dimension, you can estimate the distance between the cat and you based on the relative location of the cat in the room.
If it is a room with reverberation, you can estimate the distance by analyzing the direct sound and reverberation sound.
You can estimate the angle of the cat below your horizon, and then calculate the horizontal distance between you and the cat by simple trigonometry using your height and the angle.
You can use cat treats to attract the cat to walk/run to you, and estimate the original distance by the cat’s running speed and the time it takes to get to you.
You can walk to the cat, and estimate the distance by the your walking speed and the time it takes for you to reach the cat
And many other ways.
Because there are so many “cues” that we can use for simple judgements like this, there are a lot of studies looking at each individual cue, the interaction between cues, and the integration of cues. Although it is often a struggle for me to obtain a clear and consistent story from the numerous studies, I found it interesting that after the long history of evolution, we still keep such a “redundant” system.
This system is probably redundant in a rich environment. For example, when your own cat is meowing at you from the cat tree in your own house, you probably don’t need any reasoning or mental calculation to estimate the distance. However, when a cat is meowing at you with very low volume in the wild, you probably need to start from asking “is that a cat?” Whatever the situation is, however rich or impoverished the cues are, we gather every evidence we can get, compare which cues are more reliable, and make our best guess. Such strategy is exactly the same as what people with sensory loss would use.
Sensory impairment is part of human diversity. Our habit of putting a borderline between “normal” and “impaired” might block us from seeing the entire spectrum, and the nature of well-controlled and fine-grained laboratory studies might make us ignore the world beyond fixation. My thoughts here have probably wandered too far from the original simple statement in the museum. But I really like this new perspective, which has helped me looking at sensory impairment and my research from a complete new point of view.