James F. Reichert

Does Environmental Enrichment Reduce Stress? An Integrated Measure of Corticosterone from Feathers Provides a Novel Perspective

Enrichment is widely used as tool for managing fearfulness, undesirable behaviors, and stress in captive animals, and for studying exploration and personality. Inconsistencies in previous studies of physiological and behavioral responses to enrichment led us to hypothesize that enrichment and its removal are stressful environmental changes to which the hormone corticosterone and fearfulness, activity, and exploration behaviors ought to be sensitive. We conducted two experiments with a captive population of wild-caught Clarks nutcrackers (Nucifraga columbiana) to assess responses to short- (10-d) and long-term (3-mo) enrichment, their removal, and the influence of novelty, within the same animal. Variation in an integrated measure of corticosterone from feathers, combined with video recordings of behaviors, suggests that how individuals perceive enrichment and its removal depends on the duration of exposure. Short- and long-term enrichment elicited different physiological responses, with the former acting as a stressor and birds exhibiting acclimation to the latter. Non-novel enrichment evoked the strongest corticosterone responses of all the treatments, suggesting that the second exposure to the same objects acted as a physiological cue, and that acclimation was overridden by negative past experience. Birds showed weak behavioral responses that were not related to corticosterone. By demonstrating that an integrated measure of glucocorticoid physiology varies significantly with changes to enrichment in the absence of agonistic interactions, our study sheds light on potential mechanisms driving physiological and behavioral responses to environmental change.

Use of local and global geometry from object arrays by adult humans

Disoriented men and women were trained to search for a goal hidden in front of one of four objects forming a rectangular-shaped array. The angular properties of these objects (either 50° or 75°) served as local geometric cues and the rectangular shape of the array served as global geometric cues. Upon successful completion of training, transformation tests were conducted during which either the local angle cues were removed and the global geometry was preserved (Global Cues test) or the local angles were preserved and the global geometry was removed (Local Cues test). A Cue Conflict test was also conducted which placed the local geometry in direct competition with the global geometry for control of search behavior. Results from testing showed that neither men nor women could successfully use only the global geometric cues provided by the shape of the array to reorient. Analyses of sex differences for the use of local cues revealed that men showed clear evidence that they had successfully encoded the local angular cues whereas women did not. Furthermore, the size of the training angle may have affected the encoding of local cues.

Discrimination of geometric angles by adult humans

Men and women learned to discriminate between two different size angles presented to them as objects within a real-world task. During Experiment 1, participants in group 50 were trained to choose a 50° angle and participants in group 75 were trained to choose a 75° angle. During testing, both groups were provided with a choice between their training angle and one of a set of test angles that was either smaller or larger than the training angle. Results showed a generalized pattern of responding, with group 50 showing increased responding to test angles smaller than 50° and group 75 showing increased responding to test angles larger than 75°. Further analysis of the response patterns revealed that participants in group 50 showed evidence of absolute learning, whereas participants in group 75 showed evidence of relational learning. During Experiment 2, a third group of participants (group 25) trained to choose a smaller angle (25°) was included in addition to group 50 and group 75. Participants were trained with three angles present and tested with just two, one being their training angle and the other being one of a set of novel test angles. Similar to the participants from Experiment 1, group 75 showed evidence of relational learning. Group 50, for which no relational rule could be applied during training, showed an absolute learning pattern with no response shift to test angles smaller or larger than their training angle. Group 25 showed evidence of absolute responding that was more pronounced than that found for the smallest training angle during Experiment 1. These findings suggest differential learning of geometric angles based on amplitude with smaller angles perceived as more distinct and thus more resistant to broader generalization than larger angles. Implications of these results are that certain geometric properties may be subject to different learning processes based on the specific magnitude of that property.

Reorienting in virtual 3D environments: do adult humans use principal axes, medial axes or local geometry?

Studies have shown that animals, including humans, use the geometric properties of environments to orient. It has been proposed that orientation is accomplished primarily by encoding the principal axes (i.e., global geometry) of an environment. However, recent research has shown that animals use local information such as wall length and corner angles as well as local shape parameters (i.e., medial axes) to orient. The goal of the current study was to determine whether adult humans reorient according to global geometry based on principal axes or whether reliance is on local geometry such as wall length and sense information or medial axes. Using a virtual environment task, participants were trained to select a response box located at one of two geometrically identical corners within a featureless rectangular-shaped environment. Participants were subsequently tested in a transformed L-shaped environment that allowed for a dissociation of strategies based on principal axes, medial axes and local geometry. Results showed that participants relied primarily on a medial axes strategy to reorient in the L-shaped test environment. Importantly, the search behaviour of participants could not be explained by a principal axes-based strategy.

Angular amplitude matters: Exploring the functional relationship of geometric cue use by Clark's nutcrackers (Nucifraga columbiana)

Four groups of Clarks nutcrackers (Nucifraga columbiana) learned to search for food hidden at one of two geometrically identical corners of a parallelogram-shaped enclosure. The corners of the enclosure projected either 40° and 140° angles or 60° and 120° angles. Tests using both rhomboid and rectangular enclosures examined whether birds had encoded angular amplitude and the length of walls, respectively. Cue conflict tests using a mirror-image of the training parallelogram reversed the relationship between wall length and corner angle, allowing for the examination of cue weighing. Furthermore, cue conflict tests which manipulated the angular amplitude allowed for the investigation of whether the encoding of angular information was similar among the training groups. Our results showed that nutcrackers encoded both angular amplitude and wall length. During cue conflict tests that maintained the training angular amplitudes, birds did not show a strong weighing of angular cues at a population-level but rather considerable individual differences were found. Finally, manipulating angular amplitude in the direction towards the unrewarded angle resulted in reduced weighing of angular cues whereas manipulating angular amplitude in the direction away from the unrewarded angle resulted in greater weighing of angular cues. In summary, our results support the importance of using multiple exemplars during training and testing to better understand the functional relationship between geometric cues during a spatial search task.

How Clark's nutcrackers (Nucifraga columbiana) weigh geometric cues depends on their previous experience.

Abstract Following passive disorientation, Clark’s nutcrackers (Nucifraga columbiana) learned to search for a hidden food reward located in one corner of a rectangular-shaped enclosure that contained either identical or distinct features in each corner. Identical features allowed for explicit learning of geometric cues, whereas distinct features allowed for both explicit learning of featural cues and incidental learning of geometric cues. Birds that only learned about geometry incidentally (group Distinct) weighed features greater than geometry when the two cues were placed in conflict. However, birds that received explicit training with geometry, in addition to feature training (groups Distinct–Identical and Identical–Distinct), weighed geometry heavier relative to features. Cue preference by the birds also depended on the order in which learning was experienced; if explicit training with geometry followed that of features (group Distinct–Identical), then both geometry and features were weighed equally, but if explicit training with geometry training preceded that of features (group Identical–Distinct), the birds weighed geometry greater than features. Results suggest both a heightened sensitivity to geometric cues by Clark’s nutcrackers relative to other species of birds and an increased sensitivity to any spatial cue (either features or geometry) that has proven both stable and reliable.

Orientation in Virtual Reality Does Not Fully Measure Up to the Real-World

Adult participants learned to reorient to a specific corner inside either a real or virtual rectangular room containing a distinct featural object in each corner. Participants in the virtual-reality (VR) condition experienced an immersive virtual version of the physical room using a head-mounted display (HMD) and customized manual wheelchair to provide self-movement. Following a disorientation procedure, people could reorient by using either the geometry of the room and/or the distinct features in the corners. Test trials in which the different spatial cues were manipulated revealed participants encoded features and geometry in both the real and VR rooms. However, participants in the VR room showed less facility with using geometry. Our results suggest caution must be taken when interpreting the nuances of spatial cue use in virtual environments. Reduced reliability of geometric cues in VR environments may result in greater reliance on feature cues than would normally be expected under similar real-world conditions.