Humans were able to accurately use dead-reckoning to estimate distance and direction on a smaller scale. Participants modulated their peak speed on the homeward path. Increased circuity of the outbound path resulted in an increase in absolute heading error. Rats were able to use self-movement cues to estimate distance and direction to the start location. Similarly, rats modulated their peak speed on the homeward path. Increases in outbound path circuity resulted in an increase in absolute heading error. Accurate distance and direction estimation in both species suggests a role for movement segmentation when using self-movement cues. The use of this task in translational neuroscience may provide valuable insight to the complex relationship between neurodegenerative disorders and spatial orientation. References: Wallace, D., Choudry, S. & Martin, M. (2006). Comparative analysis of movement characteristics during dead-reckoning-based navigation in humans and rats. Journal of Comparative Psychology, Navigating with fingers and feet: Distance and direction estimation in non-visual spatial tasks J.R. Raines, S.J. Wagner, J.L. Jones, A.N. Patel, S.S. Winter, D. Clarke, D.G. Wallace* Dept Psychology, Northern Illinois Univ., DeKalb, IL, USA Human participants were blindfolded while seated at a rectangular table and asked to search the table-top for a piece of Velcro using their index finger across six trials. Upon finding the Velcro, they were instructed to return to the start location. The participants were divided into three groups [short (n=10), medium (n=10) and long (n=10)] relative to the lengths between the Velcro and the start position. In addition, female Long Evans rats (n=7) were trained to search a table-top for a food pellet at varying distances under dark conditions. The rats then returned to the home base with the food pellet. This continued for three sessions, in which each session consisted of five randomly placed food pellets. Figure 2: Topographic (top panels) and kinematic (bottom panels) profiles of outward and homeward segments are plotted for one subject in each group. The groups reflected the distance from the start to the goal location and were categorized as being short (0.18 m), medium (0.42 m) or long (0.57 m). Spatial orientation depends on the accurate processing of multiple sources of information. For example, dead reckoning based navigation involves online processing of self-movement cues to return to the point where movement originated. Previous work has shown that disruption in human movement segmentation (i.e., indirect relationship between linear speed and path curvature) during a blindfolded walking task was associated with impaired direction estimation (Wallace, Choudry & Martin, 2006). Observing that movement segmentation influences direction estimation on a smaller scale would demonstrate that it is a general characteristic of guided movements. In addition, movement kinematics have been shown to vary based on movement distance during non-visually guided planar reaching tasks. The current study investigated direction and distance estimation in humans and rats when restricted to only using self-movement cues in analogous searching tasks. Correspondence: D.G. J.R. Web: Figure 3: Average absolute heading error (left panel) and average homeward peak speed (right panel) are plotted relative to the path circuity of the outbound segment and groups. Increases in path circuity resulted in increases in absolute heading error. Outbound segment path circuity did not influence the peak speed of the homeward segment. Additionally, increases in distance between the start and goal location resulted in increases in the peak speed of the homeward segment. There was no effect of distance on absolute heading error. Figure 1: A single trial is plotted for the human searching task (left-hand panel) and the rat searching task (right-hand panel) /FF134 Figure 4: Topographic (top panels) and kinematic (bottom panels) profiles of outward and homeward segments are plotted for one rat. The distances varied from the start to the food pellet (goal location) and were categorized as being short (~0.95 m), medium (~1.54 m) or long (~2.10 m). Figure 5: Average absolute heading error (top panels) and average homeward speed (bottom panels) for the rats are plotted relative to distance from the food pellet and path circuity of the outbound segment. Increases in path circuity resulted in increases in absolute heading error but not peak speed. Additionally, increases in distance between the start and goal location resulted in increases in the peak speed of the homeward segment but not heading error. Abstract Methods Results Conclusions Figure 6: Movement segmentation, or the relationship between linear speed and path curvature, is plotted for humans (top left panel) and rats (top right panel). For both species, as linear speed increased path curvature decreased. Absolute heading error for the homeward segment from humans (bottom left panel) and rats (bottom right panel) are plotted in relation to outward movement segmentation for the current searching task and a previously reported triangle completion task. Both tasks demonstrated that high amounts of movement segmentation on the outbound path result in a decrease in absolute heading error. A functional role for adult hippocampal neurogenesis in spatial pattern separation