Decoding of spatial proportions using somatosensory feedback in sighted and visually impaired children

Background and purpose: Humans can naturally operate with ratios of continuous magnitudes (proportions). We asked if sighted children (S) and visually impaired children (VI) can discriminate proportions via somatosensory feedback.

Procedures: Children formed a proportion by tracing a pair of straight lines with their finger, and compared this proportion with a second proportion resulting from the tracing of another pair of lines.

Main findings: Performance was 68% in S, thus significantly lower (p < 0.001) compared to VI (75%). Tracing velocity (p < 0.01) and trial-to-trial variability of tracing velocity (p < 0.05) was higher in S compared to VI.

Conclusions: Operating with proportions solely from somatosensory feedback is possible, thus tracing lines might support learning in mathematics education. Kinematic variables point to the reason for the difference between S and VI, in that higher trial-to-trial variability in velocity in S leads to biased estimation of absolute line lengths.