The Traveling Salesman Problem in the Natural Environment

Is it possible for humans to navigate in the natural environment wherein the path taken between various destinations is 'optimal' in some way? In the domain of optimization this challenge is traditionally framed as the "Traveling Salesman Problem" (TSP). What strategies and ecological considerations are plausible for human navigation? When given a two-dimensional map-like presentation of the destinations, participants solve this optimization exceptionally well (only 2-3% longer than optimum)^1, 2^. In the following experiments we investigate the effect of effort and its environmental affordance on navigation decisions when humans solve the TSP in the natural environment. Fifteen locations were marked on two outdoor landscapes with flat and varied terrains respectively. Performance in the flat-field condition was excellent (∼6% error) and was worse but still quite good in the variable-terrain condition (∼20% error), suggesting participants do not globally pre-plan routes but rather develop them on the fly. We suggest that perceived effort guides participant solutions due to the dynamic constraints of effortful locomotion and obstacle avoidance

The perception of surface orientation from multiple sources of optical information

An orientation matching task was used to evaluate observers ’ sensitivity to local surface orientation at designated probe points on randomly shaped 3-D objects that were optically defined by texture, lambertian shading, or specular highlights. These surfaces could be stationary or in motion, and they could be viewed either monocularly or stereoscopically, in all possible combinations. It was found that the deformations of shading and/or highlights (either over time or between the two eyes’ views) produced levels of performance similar to those obtained for the optical deformations of textured surfaces. These findings suggest that the human visual system utilizes a much richer array of optical information to support its perception of shape than is typically appreciated

Effects of Post-Weaning Social Isolation and Oxytocin on Adult Anxiety and Sociability in Female Rats

Positive social interactions during childhood and adolescence are essential for human neurobehavioral development. All social animals show persistent physiological and behavioral deficits after extended periods of social isolation. Our goal was to determine whether post-weaning social isolation negatively impacts adult anxiety and sociability in female Long Evans rats. Additionally, we tested whether administration of the pro-social hormone, oxytocin, could prevent behavioral deficits induced by isolation. On post-natal day (PND) 21, subjects were randomly assigned to social isolation (n = 30) or group housing (n = 30). Half of the subjects in each housing condition received 1 mg/kg oxytocin every three days for thirty days. The other half received saline-vehicle control. On PND 51-52, anxiety was assessed in the elevated-plus-maze (EPM). Subjects were then group housed (“resocialization”) in novel triplets. Due to the potential influence of ovarian hormones on social motivation, daily vaginal cytology was initiated to track subjects’ estrous cycles. On PND 66-67, subjects completed a second EPM test. On PND 70-72, subjects’ social motivation was assessed using a three-chamber sociability apparatus. Isolated subjects exhibited higher anxiety in the first EPM test (immediately following isolation) compared to group housed subjects (p < 0.01). In the second EPM test, however, there were no group differences in anxiety, suggesting that the detrimental effects of post-weaning social isolation on anxiety had been redressed by resocialization. Also as predicted, previously isolated subjects exhibited reduced social motivation compared to group-housed subjects (p < 0.05). These findings suggest that post-weaning isolation leads to persistent social deficits that cannot be explained by an increase in generalized anxiety. Lastly, oxytocin treatment did not prevent the detrimental behavioral effects of post-weaning social isolation, which suggests that the developmental consequences of adolescent social deprivation may not be caused by reduced oxytocin output. Overall, this study substantiates the theory that early social isolation has detrimental effects on adult emotionality and behavior. Future animal research should continue to explore the potential clinical utility of oxytocin in treating social deficits

Is the Perception of 3D Shape from Shading Based on Assumed Reflectance and Illumination?

The research described in the present article was designed to compare three types of image shading: one generated with a Lambertian BRDF and homogeneous illumination such that image intensity was determined entirely by local surface orientation irrespective of position; one that was textured with a linear intensity gradient, such that image intensity was determined entirely by local surface position irrespective of orientation; and another that was generated with a Lambertian BRDF and inhomogeneous illumination such that image intensity was influenced by both position and orientation. A gauge figure adjustment task was used to measure observers' perceptions of local surface orientation on the depicted surfaces, and the probe points included 60 pairs of regions that both had the same orientation. The results show clearly that observers' perceptions of these three types of stimuli were remarkably similar, and that probe regions with similar apparent orientations could have large differences in image intensity. This latter finding is incompatible with any process for computing shape from shading that assumes any plausible reflectance function combined with any possible homogeneous illumination