Katherine A. Gaskin

Incidental encoding of enclosure geometry does not require visual input: evidence from blindfolded adults

Although spatial orientation with respect to the geometric properties of an environment appears to be an ability shared across various species, debate remains concerning potential similarities and differences with respect to the underlying mechanism(s). One prominent theoretical account of orientation with respect to the environment suggests that participants match visual memories to their current visual perception and navigate to reduce the discrepancy between the two. We tested whether visual input was necessary to incidentally encode the geometric properties of an environment, by training disoriented and blindfolded adult participants to search by touch for a target object hidden in one of four locations, marked by distinctive textural cues, located in the corners of a rectangular enclosure. Following training, we removed the distinctive textural cues and probed the extent to which the participants had learned the geometry of the enclosure. Even in the absence of vision and unique textural cues, search behavior was consistent with evidence for the encoding of enclosure geometry. A follow-up experiment in which participants were trained in a rectangular enclosure but were tested in a square enclosure provided converging evidence that search behavior was influenced by the geometric properties of the enclosure. Collectively, these results suggest that even in the absence of vision, participants incidentally encoded the geometric properties of the enclosure, indicating that visual input is not required to encode the geometric properties of an environment.

More than a Feeling: Incidental Learning of Array Geometry by Blindfolded Adult Humans Revealed through Touch

SUMMARY View-based matching theories of orientation suggest that mobile organisms encode a visual memory consisting of a visual panorama from a target location and maneuver to reduce discrepancy between current visual perception and this stored visual memory to return to a location. Recent success of such theories to explain the orientation behavior of insects and birds raises questions regarding the extent to which such an explanation generalizes to other species. In the present study, we attempted to determine the extent to which such view-based matching theories may explain the orientation behavior of a mammalian species (in this case adult humans). We modified a traditional enclosure orientation task so that it involved only the use of the haptic sense. The use of a haptic orientation task to investigate the extent to which view-based matching theories may explain the orientation behavior of adult humans appeared ideal because it provided an opportunity for us to explicitly prohibit the use of vision. Specifically, we trained disoriented and blindfolded human participants to search by touch for a target object hidden in one of four locations marked by distinctive textural cues located on top of four discrete landmarks arranged in a rectangular array. Following training, we removed the distinctive textural cues and probed the extent to which participants learned the geometry of the landmark array. In the absence of vision and the trained textural cues, participants showed evidence that they learned the geometry of the landmark array. Such evidence cannot be explained by an appeal to view-based matching strategies and is consistent with explanations of spatial orientation related to the incidental learning of environmental geometry.

Overtraining and the use of feature and geometric cues for reorientation

Using a dynamic three-dimensional virtual environment task, we investigated the influence of overtraining of feature and geometric cues on preferential spatial cue use. We trained two groups of human participants to respond to feature and geometric cues in separate enclosures before placing these cues in conflict on a critical test trial. All participants learned to respond to rewarded features located along the principal axis of a rectangular search space and to rewarded geometric cues of a rectangular search space in separate training phases followed by a single test trial. During the test trial, we situated the rewarded features in the unrewarded geometric corners and the unrewarded features in rewarded geometric corners. For one group, participants were overtrained with feature cues compared to geometric cues before experiencing the conflict test; whereas, for another group, participants were overtrained with geometric cues compared to feature cues before experiencing the conflict test. Although both groups learned to respond to both feature and geometric cues at an equivalent rate and to an equivalent level of terminal accuracy, testing results revealed no difference between the groups with respect to their preference for feature or geometric cues. Despite a lack of influence of overtraining on spatial cue preference, participants showed an overall preference for feature cues. We discuss the results with respect to implications for theoretical accounts of spatial learning.

Beacons and surface features differentially influence human reliance on global and local geometric cues when reorienting in a virtual environment.

In the reorientation literature, non-geometric cues include discrete objects (e.g., beacons) and surface-based features (e.g., colors, textures, and odors). To date, these types of non-geometric cues have been considered functionally similar, and it remains unknown whether beacons and surface features differentially influence the extent to which organisms reorient via global and local geometric cues. In the present experiment, we trained human participants to approach a location in a trapezoid-shaped enclosure uniquely specified by global and local geometric cues. We explored the role of beacons on the use of geometric cues by training participants in the presence or absence of uniquely-colored beacons. We explored the role of surface features on the use of geometric cues by recoloring two adjacent walls at the correct location and/or adding a line on the floor which corresponded to the major principal axis of the enclosure. All groups were then tested in novel-shaped enclosures in the absence of unique beacons and surface features to assess the relative use of global and local geometric cues. Results suggested that beacons facilitated the use of global geometric cues, whereas surface features either facilitated or hindered the use of geometric cues, depending on the feature.