Effects of sight impairment on comprehension of scale

By Suzanne Perin - October 2011


Jones, M. G., Taylor, A. R., & Broadwell, B. (2009). Concepts of scale held by students with visual impairment. Journal of Research in Science Teaching, 46(5), 506–519.


Size and scale are important concepts across disciplines, particularly with recent advances at the very large and very small ends of the continuum, which are also hard to teach and understand. Since not much is known about how people develop a sense of linear size and scale, particularly for children with visual impairments, the authors compared their accuracy to that of non-visually impaired students, as well as examined their experiences learning about size in- and out-of-school. The authors speculate that educators may find students with visual impairments to have unique accessibility to concepts of the very large and small scales of science.

Children with visual impairments must use other senses, hearing and touch in particular, to navigate the world, and so must develop a highly attuned sense of personal and environmental space at the human scale. Given this constraint, the authors wondered how visually impaired children conceptualized orders of magnitude larger and smaller than themselves. They were interested in this question partly in terms of whether answering it might yield insights that could inspire new, non-visual ways of communicating scales that lie outside of the experiential realm for all people.

Two questions guided this study: (1) How accurate were visually impaired students’ conceptualizations of spatial sizes of objects and distances over many orders of magnitude compared to students with normal vision? and (2) What experiences about learning size and scale had students with visual impairments had in- and out-of- school? As many as 17 middle- and high-school students who were blind and received educational services to accommodate their disability were recruited from within a 2-day camp offered at a large southeastern university. They completed a series of assessments, which were then compared to results from a previous study of participants who did not have impaired sight.

The study found that visually impaired students were most accurate with near human-sized measurements (centimetres to 10 meters). Furthermore, the analysis showed that the visually impaired students were better than normally sighted students at very large and small scales (using metric and body scales, e.g., naming an object that was 10 times their body length). When asked about how they learned about the sizes of things, they reported a variety of ways, including hearing teachers talk about size, measuring things and learning from family members. The authors conjecture that visually impaired students may be better at these extreme scales because they have had more experience learning about these sizes or that size and scale is more important to them so that they cue into information about size and/or remember it better than normally sighted peers.

The authors provide the following implications for educators:

• At the ends of the scale where sight is of minimal use (large and small), the authors speculate that language-based or model-based instruction may be the effective way to teach both normally and visually impaired students about the extremes of scale. 

• Incorporating senses, other than sight, could help all students. At the small scales, haptic (tactile) and auditory senses are primary means of perceiving scale; and at the large scale, kinaesthetic and auditory senses are used (e.g., using canes to navigate).