Spontaneous Perception of Whole Persons According the Distance Samuel Demarchi Laboratoire Parisien de Psychologie Sociale (EA 4386) Université Paris 8, France. samuel.demarchi@univ-paris8.fr Anaïs Taddeï Laboratoire Cognition Humaine et Artificielle Université Paris 8, France. anais.taddei@gmail.com Charlie Frowd School of Psychology University of Central Lancashire, UK. cfrowd@uclan.ac.uk Abstract In the field of automated facial identification, relevant facial information are not always available (disguises, poor spatial orientation, distance, etc.). As a consequence, human perception performance decreases. However, the "whole person" can provide useful information. In the present study, we determine the way by which a person is visually explored, in order to identify a potential chronology in visual exploration. We also investigate the consequence of increasing the distance between the observer and the target person, since in this situation identification becomes more ‘global’ due to less processing possible for the individual features of the face. Results showed that the spontaneous perceptual strategy evolves with distance: the more distance increases, the more the interest in the person decreases, which is observed both for the body and face. Our data provide knowledge that will help to guide conception of effective automated systems. 1. Introduction The use of video for automated identification of criminals is a booming industry. Current surveillance systems can detect the presence of a person sought by the police in a public place, analyzing person characteristics such as face or gait [1,2,3,4]. However, no system is yet fully autonomous. Current performance depends on the ability of humans to integrate information. Computer systems analyze and are able to give a warning (presence of a wanted person, motion detection, crossings, misinterpretation, poaching, etc.), but an operator is still required to make a decision in this process. We postulate that the evolution of human beings allows us to select—by the processes of selection, competition and trial-and-error—the most efficient perceptual processing strategy. In fact, the majority of analysis systems of automatic perception and identification try to emulate natural human functions. For example, automatic facial recognition is more efficient when algorithms analyze faces holistically, as evidenced by how we naturally recognize familiar faces [5,6]. In cases where facial information is unavailable (due to disguise, misdirection of the camera relative to the face, or where the face is simply occluded by an object), we have to use other methods to estimate identity, such as the “silhouette” technique described below [7,8,9,10]. However, there is not, to our knowledge, studies that specifically focus on the visual exploration of the whole person or body shape. Therefore, it is difficult to propose effective techniques. A fundamental characteristic of identification is the distance between the stimulus (target) and the video acquisition device. Currently, cameras already installed may not provide sufficient accuracy when distance increases, and high-definition cameras are expensive, thus hindering installation by states, communities and businesses. The lack of precision due to remoteness is therefore of interest. A fairly-recent study [11] has shown that we do not process faces in the same way with changing distance, due to variation in spatial frequency. Up close, high spatial frequencies (HSF) are not filtered [12,13]. By contrast, when distance increases, the environment naturally filters these high frequencies to present only the lower, less accurate frequencies. In other words, detailed information conveyed by high spatial frequencies are not visible from far away, and we see only an imprecise shape due to the predominant presence of low spatial frequencies (LSF). Thus, the greater the distance, the more the identification tasks will be based on treatment of LSF when perceiving the whole person, thus corresponding to a “silhouette”. So, if the exploration of a person depends on the spatial frequency, we should be able observe differences between conditions about the duration of fixation and areas of interest (AOI). Specifically, it is expected that, for a distant person, a global, holistic treatment will occur because it is the only possible processing due to natural low spatial frequencies filtering. When a person is seen close up, due to the presence of high spatial frequencies, 2012 Third International Conference on Emerging Security Technologies 978-0-7695-4791-6/12 $26.00 © 2012 IEEE DOI 10.1109/EST.2012.28 33 2012 Third International Conference on Emerging Security Technologies 978-0-7695-4791-6/12 $26.00 © 2012 IEEE DOI 10.1109/EST.2012.28 33