The 4D Space-Time Dimensions of Facial Perception

Abstract

Facial information is a powerful channel for human-to-human communication. Characteristically, faces can be defined as biological objects that are four-dimensional (4D) patterns, whereby they have concurrently a spatial structure and surface as well as temporal dynamics. The spatial characteristics of facial objects contain a volume and surface in three dimensions (3D), namely breadth, height and importantly, depth. The temporal properties of facial objects are defined by how a 3D facial structure and surface evolves dynamically over time; where time is referred to as the fourth dimension (4D). Our entire perception of another's face, whether it be social, affective or cognitive perceptions, is therefore built on a combination of 3D and 4D visual cues. Counterintuitively, over the past few decades of experimental research in psychology, facial stimuli have largely been captured, reproduced and presented to participants with two dimensions (2D), while remaining largely static. The following review aims to advance and update facial researchers, on the recent revolution in computer-generated, realistic 4D facial models produced from real-life human subjects. We delve in-depth to summarize recent studies which have utilized facial stimuli that possess 3D structural and surface cues (geometry, surface and depth) and 4D temporal cues (3D structure + dynamic viewpoint and movement). In sum, we have found that higher-order perceptions such as identity, gender, ethnicity, emotion and personality, are critically influenced by 4D characteristics. In future, it is recommended that facial stimuli incorporate the 4D space-time perspective with the proposed time-resolved methods.

Assessing Automated Facial Action Unit Detection Systems for Analyzing Cross-Domain Facial Expression Databases

“…Therefore, further development of RGB analyses or other information to subtly differentiate these AUs is desired. For example, depth information on the spatial characteristics of facial objects in three dimensions (3D: see [ 53 ]) and rendering technology targeted to diffuse albedo that encodes blood flow [ 54 ] would be useful for accurately detecting wrinkles and tension in parallel.…”

Facial cosmetic injection: A bibliometric analysis of research status and hotspots

“…Dynamic 3D photography, also known as 4Dimaging (4Dimaging), refers to the integration of temporal dimension into 3D imaging (3D imaging plus time axis) 19 . The utilization of real‐time and dynamic observation capabilities in 4D imaging provides a plethora of additional information compared to static 3D imaging 19 . The technology of facial imaging will play a crucial role in the preoperative simulation and postoperative evaluation process, particularly in the field of cosmetic injection, as the perioperative procedure relies more on the experience of doctors rather than quantitative assessment 20 .…”

“…18 Dynamic 3D photography, also known as 4Dimaging (4Dimaging), refers to the integration of temporal dimension into 3D imaging (3D imaging plus time axis). 19 The utilization of real-time and dynamic observation capabilities in 4D…”

“…imaging provides a plethora of additional information compared to static 3D imaging. 19 The technology of facial imaging will play a crucial role in the preoperative simulation and postoperative evaluation process, particularly in the field of cosmetic injection, as the perioperative procedure relies more on the experience of doctors rather than quantitative assessment. 20 Moreover, it will aid in identifying early signs of facial aging as well as gaining insights into mechanisms underlying facial aging across different countries and ethnicities.…”

Face Perception

“…Nonetheless, approaches based on 3D shape are also available (Vetter & Walker, 2011) and some are beginning to incorporate movement as well (A. Burt & Crewther, 2020). Haxby et al (2000) used personal identity as a paradigmatic example of an invariant facial characteristic, but there are other relatively invariant properties such as age, gender and racial background that are highly salient for human perceivers Yan et al, 2017).…”