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Speech delivered by William C. Sullivan, Chief Inspector of the Federal Bureau of Investigation, at the 1961 Pepperdine College Freedom Forum. ; x1961

S. Kaplan suggested that one outcome of mental fatigue may be an increased propensity for outbursts of anger and even violence. If so, contact with nature, which appears to mitigate mental fatigue, may reduce aggression and violence. This study investigated that possibility in a setting and population with relatively high rates of aggression: inner-city urban public housing residents. Levels of aggression were compared for 145 urban public housing residents randomly assigned to buildings with varying levels of nearby nature (trees and grass). Attentional functioning was assessed as an index of mental fatigue. Residents living in relatively barren buildings reported more aggression and violence than did their counterparts in greener buildings. Moreover, levels of mental fatigue were higher in barren buildings, and aggression accompanied mental fatigue. Tests for the proposed mechanism and for alternative mechanisms indicated that the relationship between nearby nature and aggression was fully mediated through attentional functioning.

Although vegetation has been positively linked to fear of crime and crime in a number of settings, recent findings in urban residential areas have hinted at a possible negative relationship: Residents living in "greener" surroundings report lower levels of fear, fewer incivilities, and less aggressive and violent behavior. This study used police crime reports to examine the relationship between vegetation and crime in an inner-city neighborhood. Crime rates for 98 apartment buildings with varying levels of nearby vegetation were compared. Results indicate that although residents were randomly assigned to different levels of nearby vegetation, the greener a building's surroundings were, the fewer crimes reported. Furthermore, this pattern held for both property crimes and violent crimes. The relationship of vegetation to crime held after the number of apartments per building, building height, vacancy rate, and number of occupied units per building were accounted for.

Overuse of portable electronic devices depletes one's attention capacity, a critical cognitive resource. Although contact with nature promotes attentional functioning, we do not know the extent to which exposure to nature and the use of electronic devices interact to promote or inhibit attentional functioning. In this study, 81 participants performed cognitive tasks and then were randomly assigned to one of four rest treatments: green settings with or without a laptop computer and barren settings with or without a laptop computer. Attention was measured three times. Analysis showed a significant effect for both setting and use of a laptop as well as a significant interaction between setting and laptop use. A further analysis controlling for time spent focused on the laptop screen produced similar results. The findings show that using an electronic device in green settings substantially counteracts the attention enhancement benefits of green spaces.

Defensible space (DS) theory proposes that the built environment can promote neighborhood safety and community by encouraging residents' appropriation of near-home space. This article examined the relationship between three different forms of resident appropriation and residents' experiences of neighborhood safety and community. Results from a survey of 91 public housing residents living in moderately defensible spaces suggested that residents who defended near-home space through territorial appropriation experienced the neighborhood as a safer, more cohesive community than did residents who did not appropriate space in this way. Residents who spent more time outside experienced the neighborhood as a safer place; however, casual social interaction in near-home space was not consistently related to outcomes. While no causal information is available from the correlational data presented here, this work takes an important step of providing empirical evidence of a systematic link between certain aspects of resident appropriation and positive outcomes. Implications for DS theory and for public housing policy are discussed.

How would inner-city residents respond to the incorporation of trees and grass in their neighborhoods? Law enforcement officials have argued that, in these settings, trees and other forms of vegetation increase fear. Tree density, tree placement, and levels of grass maintenance were manipulated in photo simulations of neighborhood outdoor space. One hundred residents of Chicago's Robert Taylor Homes living adjacent to the space rated the images with respect to preference and sense of safety. Although tree placement (subspaces created by trees, formality of arrangement) had little effect on sense of safety and no effect on preference, both tree density and grass maintenance had strong effects on preference and sense of safety (η2s from .49 to .89). Surprisingly, tree density and grass maintenance increased both preference and sense of safety. Results suggest that-contrary to some views-trees and grass maintenance can increase sense of safety in inner-city neighborhoods.

Although it is well established that viewing nature can help individuals recover from a stressful experience, the dose-response curve describing the relationship between tree cover density and stress recovery is totally unclear. A total of 160 participants engaged in a standard Trier Social Stress Test to induce stress. Participants were then randomly assigned to watch 1 of 10 three-dimensional videos of street scenes that varied in the density of tree cover (from 2% to 62%). Participants completed a Visual Analog Scale questionnaire at three points in the experiment. Analysis revealed a positive, linear association between the density of urban street trees and self-reported stress recovery, adjusted R2 = .05, F(1, 149) = 8.53, p < .01. This relationship holds after controlling for gender, age, and baseline stress levels. A content analysis of participants' written narratives revealed a similar but even stronger association. These findings suggest that viewing tree canopy in communities can significantly aid stress recovery and that every tree matters.

Many people do not seem to have interesting perceptual experiences while in contact with nature. To identify potential antecedents of positive perceptual experiences in natural settings, we investigated the role of a personal connection to nature on perceptual evaluation of preference-related environmental information in varying natural settings. The participants ( N = 77) rated three different types of images of rural forest landscapes in terms of perceived environmental information, including sense of safety, coherence, complexity, legibility, mystery, attentional restorativeness, familiarity, and preference. They also reported their personal connection to nature. The results showed that deeper personal connections to nature are associated with greater perceptual evaluations of sense of safety, legibility, mystery, and attentional restorativeness after accounting for landscape type and familiarity. A personal connection to nature is likely to enhance a person's perceptual experiences of natural landscapes.

To what extent does the density of the tree cover in a city relate to the amount of social capital among neighbors? To address this question, we linked social survey data ( N = 361) from the Baltimore Ecosystem Study with socioeconomic, urban form, and green space data at the census block group level using a geographic information system. We found a systematically positive relationship between the density of urban tree canopy at the neighborhood block group level and the amount of social capital at the individual level ( r = .241, p < .01). Multiple regression analyses showed that tree canopy added a 22.72% increase in explanatory power to the model for social capital. This research adds a new variable—neighborhood tree canopy—to the typologies of green space that affect human social connection. Trees are a relatively inexpensive and easy intervention to enhance the strength of social ties among neighbors.