Interference in geometry among people who are blind.
Tactile learners are just as vulnerable to area interference in geometry tasks as visual learners—so teach perimeter strategies explicitly.
01Research in Context
What this study did
Babai et al. (2020) asked blind and sighted adults to feel shapes. They compared the perimeter of two rectangles while the area changed.
The team wanted to know if touch would stop the area-interference error we see in vision.
What they found
Both groups made the same mistake. Larger area made perimeter feel longer, even when it was not.
Touch did not protect anyone from the illusion.
How this fits with other research
Papadopoulos et al. (2011) showed that good haptic scanning lets blind adults match sighted peers on spatial coding. That study raised hope that touch could erase visual illusions.
The same lab also found blind adults beat blindfolded sighted peers on the water-level task. That result looked like touch might beat vision.
Reuven’s null result closes the loop: haptic skill helps on some tasks, yet the area illusion still slips through.
Why it matters
If you teach perimeter to a learner who is blind, do not assume touch keeps the area illusion away. State the rule aloud: “Perimeter is only the edge.” Give guided practice with shapes that share one dimension but differ in area. Check for the error and prompt the correct response each time.
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Join Free →Before the next shapes lesson, model running a finger along only the edge while saying “This length is the perimeter—ignore the inside.”
02At a glance
03Original abstract
BACKGROUND: Geometry, a central branch of mathematics, is challenging for schoolchildren. Studies have shown that, when comparing perimeters of geometrical shapes, many sighted participants experience interference from the area variable, possibly stemming from the visual differences between the geometrical shapes. Accordingly, we hypothesized that such interference would not be observed in participants who are blind, who use the tactile modality to detect the properties of shapes. METHODS: Thirty participants, 15 who are blind and 15 with sight, explored pairs of geometrical shapes tactilely or visually, respectively, and compared areas and perimeters. RESULTS AND CONCLUSIONS: Surprisingly, accuracy and response time findings suggested that the two groups had a similar pattern of performance, and hence that area also interferes in comparison of perimeters among people who are blind.
Research in developmental disabilities, 2020 · doi:10.1016/j.ridd.2019.103517