How Green Is Seen

Numerous studies have reported the mental health benefits of contact with green landscapes. However, the mechanistic and neural bases of why such landscapes drive positive mental health outcomes have remained poorly understood until now.

“This study uses functional magnetic resonance imaging (fMRI) to enable us to understand the mechanisms and effects in a more accurate and theoretically valid way,” said Dr Bin Jiang, Associate Professor in Landscape Architecture. “By scanning the brain, we can observe that different brain parts make different levels of neural responses to the green landscapes. This study is opening a ‘black box’ that cannot be opened before.”

In 2016, Dean of the Faculty of Architecture and Chair Professor Chris Webster set up a strategic research cooperation with the Head of Department of Psychology and Chair Professor Tatia MC Lee, May Professor in Neuropsychology, and her State Key Laboratory of Brain and Cognitive Sciences. With their support and guidance, Dr Jiang had the opportunity to work with Dr Dorita Chang from the Department of Psychology to investigate the problem.

First, the research team developed the plan together based on visual materials collected by Dr Jiang in the US. Then Dr Chang designed and ran a random assignment fMRI experiment, asking participants to view one of three types of 3D image inside the fMRI device. Each type of image contains similar single-house community streets with a low (0–2.5 per cent), medium (31–40 per cent), or high (61–70 per cent) level of tree canopy density measured at eye-level. Brain activities were measured while the participant was viewing the images. In addition, the investigators conducted a photograph survey study of images in the laboratory as a supportive portion of the study.

The results indicated that viewing green landscapes that vary in terms of green-space density sparks corresponding changes in the activity of the human ventral posterior cingulate cortex in the brain that is correlated to behavioural stress-related responses.

“The study also shows that cingulate responses are engaged early in the processing cascade, influencing attentional and executive regions in a predominantly feedforward manner,” said Dr Chang. “Our data suggest a key role for this region in regulating (nature) dose-dependent changes in stress responses, potentially through its extensive connections to the prefrontal and hippocampal regions which in turn project towards the neuroendocrine system.”

Strong argument

Dr Jiang said: “In past decades, the government and society have gradually realised the health benefits of urban green landscapes. However, findings reported by previous studies were often criticised as ‘indirect’, ‘inaccurate’, or even ‘soft’. The neuroimage technology and methods can largely address those shortcomings, making a much stronger argument that the urban green landscape is critical for promoting public health and well-being.”

Understanding the impact of greenness on human health and well-being is an initial but fundamentally important step. In future studies the team intend to measure the impact of green landscape in a more detailed and comprehensive way. “The same challenges exist for researching other types of built environmental features in the city, such as street façade, ground surface, and building density,” said Dr Jiang. “This line of research is pioneering and vital for society.”

He is also leading a laboratory called ‘Virtual Reality Lab of Urban Environments and Human Health’ at the Faculty. The laboratory, which again is characterised by strong international and interdisciplinary cooperation, examines the impact of multiple characteristics of the urban environment, especially urban landscapes, on social justice, public health, and well-being.

Dr Jiang said: “We have finished several influential research projects in the past three years, including: how different types of green landscapes and land uses influence citizens’ perceived safety; how the factory environment of Foxconn influences assembly line workers’ mental health and suicide behaviour; how different types of freeway landscapes influence drivers’ mental states and driving performance; how the quality of the residential and nearby urban environment is associated with 13-year suicide rates of residents living in 151 public housing communities in Hong Kong; and how ratios of different types of green spaces at the county level are associated with the racial disparity in SARS-CoV-2 infection rates in the US.”

According to Dr Jiang and the rest of the team involved, the implications for modern architecture of the fMRI study are very important. “This study provides concrete evidence that urban green landscapes are not just pleasant ‘visual candy’ but can efficiently improve public health and well-being, and therefore I think the government and society should regard urban green landscapes as critical and low-cost ‘preventive medicine’.

“Compared to spending a tremendous amount of money and other resources on building a few ‘iconic’ and ‘high-end’ buildings and places, it would be more beneficial to the public to provide many more ‘ordinary’ green landscapes, such as neighbourhood parks and pocket gardens, in cities.”

Finally, Dr Jiang added a note for fellow architects: “I would humbly suggest that designers reduce reliance on anecdotal evidence and subjective perceptions. If we want to make society and government fully realise the significant positive or negative impacts of urban environments on public health and well-being, searching for scientific evidence from empirical studies to support our arguments is critical.”

Learn more about the Virtual Reality Lab of Urban Environments and Human Health.