The influence of the human form on visual judgements of movement

Humans live in complex societies encompassing millions of people, so social interactions dominate much of human behaviour. These interactions depend on an ability to perceive the moods, intentions and actions of other people, and visual perception is especially important in terms of the richness of the information it can provide. Research has shown that 'actions speak louder than words'; perception of movement plays a fundamental role in many social interactions. This project investigates how human visual motion perception is optimised for perceiving the actions of other people.
Psychologists and cognitive neuroscientists argue that the brain is divided into a set of anatomically distinct processing areas or modules. In the case of motion perception, primitive sensory qualities such as local direction and speed are thought to be processed in one part of the brain (mostly in the occipital lobe), and more complex social attributes such as posture, gait and dynamic facial expression are thought to be processed in another part (the temporal lobe). It is still not clear how the 'sensory' and 'social' processing modules interact. How are social attributes derived from sensory data? Do social attributes actually influence sensory processing? Answers to these general questions should have a major impact on our view of the brain as an organ which specialises in processing social interactions. The proposed research will address them by focusing on three specific issues.
1. It has long been known that inspection of a simple moving pattern, such as stripes drifting in a particular direction, affects our ability to perceive movement in other patterns for a short while afterwards. Subsequently viewed stationary patterns are liable to appear as if in motion for a short while. This kind of adaptation is conventionally attributed to changes in sensory processing, but a recent study claims that sensory adaptation can also be mediated by socially meaningful information in the form of human body postures. Such an effect would indicate a new and highly significant form of interaction between the social and sensory processing modules. A series of experiments will investigate the extent to which static visual information conveyed by human body posture can modulate basic sensory processing of movement.
2. The pace of other people's body movements and expressions during social interactions is crucial because it can indicate affective state, hostility and dishonesty. For example, a fast walking speed can indicate a high level of anxiety or aggression, while a slow walking speed can indicate the opposite. Very little is known about how the pace of natural human actions is estimated on the basis of visual information. It cannot be estimated in any straightforward way from the speed of movement in the images our eyes receive, because image motion varies dramatically with viewing distance. A series of experiments will investigate this issue by studying how visual estimates of the natural speed of body movements are affected by previous exposure to speeded-up or slowed-down human actions. These experiments will employ a novel perceptual effect.
3. Social processing of visual information culminates in a perceptual decision. For example: Is that person walking quickly or slowly? Are they walking towards me or not? All perceptual decision-making must, by definition, involve two components; perceptual information, and a decision criterion according to which the information is classified as consistent with one response ("fast") or another ("slow"). Experiments on perception mostly fail to distinguish between these two contributions to perceptual decisions, but both may make a legitimate contribution to our understanding of how visual information mediates social interactions. The proposed research will employ experimental techniques to investigate the contributions of perceptual and decisional factors to the results.

ACADEMIC IMPACT

The project will have a range of academic impacts:

Results will enhance the knowledge economy by making advances in our understanding of the fundamental brain processes which underpin human social interactions. The findings will be of interest to researchers in several disciplines including social science, vision science and decision science.

A major output of the project will be a library of videos depicting human actions with precisely defined timing properties. These videos will be made available to fellow researchers via a project web site, to promote further research and advances in our understanding of the perception of human actions.

New experimental techniques developed in the project aim to assess the contributions of perceptual bias and decision bias to visual judgements. These techniques and their results will promote further research on the origin of biases in the growing field of decision science, which aims to study the factors which influence human judgements and choices.

The post-doctoral assistant funded by the project will receive experience and training in novel techniques to study the perception of human actions, as well as mentoring from the PI in terms of early-researcher career development. A crucial element of career development provided by the project will be mentoring in research techniques, management, publishing and conference presentation.

ECONOMIC AND SOCIETAL IMPACT

Broader impacts of the work include the following:

New insights into the origins of social interactions, specifically relating to the hidden brain processes which allow us to judge the pace of human actions, will enrich our understanding of human behaviour and culture.

The project will generate new knowledge concerning how people adjust to changes in the dynamic visual environment by re-calibrating their perception of moving humans, vehicles and other objects in natural scenes.

Anecdotally, it seems to take some time to adjust to the pace of action when one moves to a different natural environment, such as a crowded city street full of people walking quickly, a sports event, or roads and motorways full of fast-moving vehicles. There are also subtle changes in the regular pace of actions during social exchanges in different cultures, to which one must adjust when interacting with members of those cultures (for example, the dynamic properties of gestures and expressions have been found to differ between Mediterranean and Scandinavian cultures).

The results of the project will advance our understanding beyond anecdotal accounts, and provide new insights into the brain mechanisms that mediate this 'adjustment'. The work will promote further research into the differences between environments and cultural groups, and how those differences impact on perception and decision-making. Results may also have implications for procedures designed to take account of such differences, in terms of raising awareness of cultural differences, and potential spin-off benefits for safety issues in speed judgements.