Space-time mapping on the sagittal axis in congenital blindness.

Previous evolutionary perspectives proposed that the space-time mapping on the sagittal axis originates from visuo-locomotion coupling when walking/running forward. Accordingly, the congenitally blind could not have developed a sagittal mental timeline if the latter depends on such a visuo-locomotion coupling. However, this conclusion was reached in only a single empirical study (Rinaldi et al. in J Exp Psychol General 147:444-450, 2018), and its theoretical underpinnings are not entirely convincing as locally static and continuous auditory input undergoes a relatively similar change as function of self-locomotion, but this type of sensory-locomotion coupling is spared even in congenital blindness. Therefore, the present study systematically explored whether the congenitally blind show space-time mappings on the sagittal axis using different paradigms in three experiments. In Experiment 1, using a typical implicit RT task, the congenitally blind showed the same preferred space-time mapping in the sagittal dimension as normally sighted participants did. In Experiment 2, this space-time mapping occurred even automatically when temporal relations were task-irrelevant in a naming task. In Experiment 3, in an explicit space-time mapping task, the congenitally blind were more likely to locate the past behind and the future in front of their bodies. Moreover, most blind participants used spatial metaphors for their space-time mapping on the sagittal axis. These results supported the conclusion that the congenitally blind have a sagittal mental timeline, and that their sensory-locomotion coupling experience was either more similar to that of sighted participants or not critical for the space-time mapping. The present study, thus, also helps to clarify the origin of the sagittal mental timeline.