HAPTIC MENTAL ROTATION TASKS PERFORMED BY BLIND AND SIGHTED INDIVIDUALS

Nineteen congenitally blind subjects (Ss), eleven Ss who went blind la ter in their life, and 42 control Ss with normal vision were tested in a tactile version of a ''mental rotation'' task. A specially construc ted tactile display was used which enabled a rotation of the alphanume ric symbols in multiples of 60 degrees without any form distortion. Ss had to compare two successively presented symbols regarding whether t he second was just a rotated version or also a mirror image of the fir st. Decision latencies and errors were recorded. Neither of dependent variables reveal any differences between the three groups of subjects. Moreover, the well known linear increase of decision latency as a fun ction of angular disparity could also be observed with the tactile sti muli in all three groups. Both results are consistent with the assumpt ion that mental rotation effects are neither linked to the visual moda lity nor to a manipulation of visual-analog representations. If the ta sk is solved by so called analog processes then these seem to operate with nonvisual spatial representations.