Adults' spatial scaling of tactile maps: Insights from studying sighted, early and late blind individuals

Abstract

The current study investigated spatial scaling of tactile maps among blind adults and blindfolded sighted controls. We were specifically interested in identifying spatial scaling strategies as well as effects of different scaling directions (up versus down) on participants' performance. To this aim, we asked late blind participants (with visual memory, Experiment 1) and early blind participants (without visual memory, Experiment 2) as well as sighted blindfolded controls to encode a map including a target and to place a response disc at the same spot on an empty, constant-sized referent space. Maps had five different sizes resulting in five scaling factors (1:3, 1:2, 1:1, 2:1, 3:1), allowing to investigate different scaling directions (up and down) in a single, comprehensive design. Accuracy and speed of learning about the target location as well as responding served as dependent variables. We hypothesized that participants who can use visual mental representations (i.e., late blind and blindfolded sighted participants) may adopt mental transformation scaling strategies. However, our results did not support this hypothesis. At the same time, we predicted the usage of relative distance scaling strategies in early blind participants, which was supported by our findings. Moreover, our results suggested that tactile maps can be scaled as accurately and even faster by blind participants than by sighted participants. Furthermore, irrespective of the visual status, participants of each visual status group gravitated their responses towards the center of the space. Overall, it seems that a lack of visual imagery does not impair early blind adults' spatial scaling ability but causes them to use a different strategy than sighted and late blind individuals.

Fig 1

(A) Learning times, (B) response times and (C) absolute errors as a function of scaling factors in both experiments. (D) The effect of target position on signed errors. Dependent variables are presented separately for each visual status group (Experiment 1: late blind participants vs. sighted controls, Experiment 2: early blind participants vs. sighted controls). Note. Error bars represent +/- 1 SE. Labels on the x axis from panel D mean: L1 = first from left, L2 = second from left, M = middle, R2 = second from right, R1 = first from right. Negative values of signed errors suggest that the disc was placed too far to the left on the referent space; positive values indicate that the disc was placed too far to the right on the referent space.