More than a feeling: incidental learning of array geometry by blind-folded adult humans revealed through touch

Blindfolded adults' use of geometric cues in haptic-based relocation

Non-visual information is important for navigation in limited visibility conditions. We designed a haptic-based relocation task to examine blindfolded adults' use of geometric cues. Forty-eight participants learned to locate a corner in a parallelogram frame. They were then tested in different transformed frames: (a) a reverse-parallelogram, in which locations predicted by original length information and angle information conflicted, (b) a rectangle, which retained only length information, and (c) a rhombus, which retained only angle information. Results show that access to the environment's geometry through haptic modality is sufficient for relocation. However, adults' performances in the current task were different from that in visual tasks in previous findings. First, compared to previous findings in visual-based tasks, length information lost its priority. Approximately half of the participants relied on angle information in the conflict test and the other half relied on length. Second, though participants encoded both length and angle information in the learning phase, only one cue was relied on after the conflict test. Finally, though participants encoded the target location successfully, they failed to represent the global shape of the environment. We attribute adults' different performances in haptic-based and visual-based tasks to the high cognitive demands in encoding and using haptic spatial cues, especially length information.

For humans navigating without vision, navigation depends upon the layout of mechanically contacted ground surfaces

Navigation can be haptically guided. In specific, tissue deformations arising from both limb motions during locomotion (i.e., gait patterns) and mechanical interactions between the limbs and the environment can convey information, detected by the haptic perceptual system, about how the body is moving relative to the environment. Here, we test hypotheses concerning the properties of mechanically contacted environments relevant to navigation of this kind. We studied blindfolded participants implicitly learning to perceive their location within environments that were physically encountered via walking on, stepping on, and probing ground surfaces with a cane. Environments were straight-line paths with elevated sections where the path either narrowed or remained the same width. We formed hypotheses concerning how these two environments would affect spatial updating and reorientation processes. In the constant pathwidth environment, homing task accuracy was higher and a manipulation of the elevated surface, to be either unchanged or (unbeknown to participants) shortened, biased the performance. This was consistent with our hypothesis of a metric recalibration scaled to elevated surface extent. In the narrowing pathwidth environment, elevated surface shortening did not bias performance. This supported our hypothesis of positional recalibration resulting from contact with the leading edge of the elevated surface. We discuss why certain environmental properties, such as path-narrowing, have significance for how one becomes implicitly oriented the surrounding environment.