N ATURAL VERSUS M EDIATED E NVIRONMENT

N ATURAL VERSUS M EDIATED E NVIRONMENT

Gibson’s theory provided a framework for understanding media, explaining how we perceive still and moving media, and how they relate to the natural envi- ronment. Gibson clearly separated environmental information from the creation of media which, for visuals, involves the structuring of light by individuals who select and display optical information. Affordance meanings are perceived directly in the natural environment. They can also be perceived indirectly in representations and artists have an ability to select and display information in a way that facilitates our perception of affordance meanings.

Gibson notes that the display of invariant structure in “moving” media is more important than the availability of perspective structure. For example, fi lm editing is done to preserve invariant information across sequences. We do learn to deal with editing techniques, including cuts, dissolves, fl ashbacks and fl ashforwards in time, interwoven subplots, and the like, but programs for young children wisely employ fewer and simpler types of edits.

Mediated environments, some of which make available apparent navigation, have similarities with and differences from natural environments. Theorists have iden- tifi ed different spatial zones, some of which have considerable relevance to POV motion illusions. Cutting and Vishton (1995) have described three zones—personal space, action space, and vista space — and identifi ed the dominant sources of percep- tual information within each. For example, some pictorial sources of information (occlusion, relative size, and relative density) are invariant with distance. Within action space, the circular region immediately beyond personal space where we can move and act quickly, the effective sources of perceptual information are two of the pictorial sources—occlusion and relative size, plus motion perspective, height in the visual fi eld, and binocular disparity. In simulations, motion perspective can

be created by POV camera. Action space is typically the ecological environment of action VGs. Because motion perspective dissipates with distance, Cutting and Vishton state that vista perception by a pedestrian is “generally unperturbed by the motions of the observer.” This occurs because only monocular and static sources of vista informa- tion are available in large quantity to the pedestrian. Four pictorial cues are impor- tant: occlusion, relative size, height in the visual fi eld, and aerial perspective. They note that vista space is the region in which very large paintings are most effective in either revealing layout or deceiving the eye so that extended layout is seen (e.g., Pozzo ceiling). However, some media vistas, for example, fl ight simulator VGs,

288 Joan M. Preston

permit apparent speed of movement, making motion perspective relevant as an important source of information to the participant.

Previc (1998) describes four perceptual zones. Two areas are linked to (1) grasping and manipulating within arm’s reach and (2) reading, other complex form perception and visually mediated social interactions involving facial perception. His action extrapersonal zone (AcE) is a 360° surround, where pictorial depth cues (e.g., linear perspective, relative size) tend to predominate. Previc states that the major spatial function of AcE is to orient and navigate in relation to objects and places in topographically defi ned external space. His ambient extrapersonal zone (AmE) is concerned with spatial orientation and “its mode of processing is designed to interpret self-motion within a stable world by preconscious mecha- nisms.” In contrast to the theories of Cutting and Vishton, its apparent stability does not mean that important motion processing does not occur.

The major visual cues of AmE are those important to maintaining spatial orientation and postural control: horizontal cues, linear perspective, and motion fl ow. Such wide fi eld-of-view information signals self-motion. In media simula- tions, Previc notes that the effectiveness of motion fl ow is evidenced in vection and postural changes produced by wide-FOV moving surrounds. Ambient visual processing provides critical input that complements the outputs of AmE corporeal senses (vestibular and somatosensory–proprioceptive) to achieve effective postural control, spatial orientation, and image stabilization. Stimulation of each of these senses is capable of inducing postural alterations and spatial orientation illusions in fl ight and in the simulation of cycloconvergence. Previc points out that motion information in AmE includes all 3 types of angular motion (yaw, pitch, roll) and predominantly one type of linear motion (centrifugal expanding fl ow, associated with forward locomotion). The vestibular system is the most important body-ori- entation system for AmE, because it usually provides the most reliable and valid inertial information concerning the direction of the head relative to gravity and it may be critical in establishing the left–right coordinate frame because of its funda- mental asymmetry. Previc emphasizes the importance of the AmE system because its overall body-in-space coordinates serve as the bedrock for all perceptual systems. For Previc, as well as for Gibson, the basic orienting system is essential for percep- tion and for action. It is simulation of the AmE environment where media creators may be able to infl uence the development of consciousness.