Gary E. Riccio

Visually induced motion sickness in virtual environments

Visually induced motion sickness is a syndrome that occasionally occurs when physically stationary individuals view compelling visual representations of self-motion. It may also occur when detectable lags are present between head movements and recomputation and presentation of the visual display in helmet-mounted displays. The occurrence of this malady is a critical issue for the future development and implementation of virtual environments. Applications of this emerging technology are likely to be compromised to the extent that users experience illness and/or incapacitation. This article presents an overview of what is currently known regarding the relationship between visually specified self-motion in the absence of inertial displacement and resulting illness and perceptual-motor disturbances.

Gravitoinertial Force Versus the Direction of Balance in the Perception and Control of Orientation

Curthoys and Wade (1990) appeal to land-based data in defending the traditional view that stimulation of the otolith organs leads to perception of the direction of gravitoinertial force. However, such data do not permit rejection of the hypothesis that the perception of orientation is based on the dynamically defined direction of balance, which is qualitatively different from the kinetically defined direction of gravitoinertial force. Furthermore, the approach of Curthoys and Wade is compromised by their failure to consider relations between the perception and control of orientation. Such relations must be considered in developing a general theory of orientation.

Development of the Coordination between Posture and Manual Control.

Studies have suggested that proper postural control is essential for the development of reaching. However, little research has examined the development of the coordination between posture and manual control throughout childhood. We investigated the coordination between posture and manual control in children (7- and 10-year-olds) and adults during a precision fitting task as task constraints became more difficult. Participants fit a block through an opening as arm kinematics, trunk kinematics, and center of pressure data were collected. During the fitting task, the precision, postural, and visual constraints of the task were manipulated. Young children adopted a strategy where they first move their trunk toward the opening and then stabilize their trunk (freeze degrees of freedom) as the precision manual task is being performed. In contrast, adults and older children make compensatory trunk movements as the task is being performed. The 10-year-olds were similar to adults under the less constrained task conditions, but they resembled the 7-year-olds under the more challenging tasks. The ability to either suppress or allow postural fluctuations based on the constraints of a suprapostural task begins to develop at around 10 years of age. This ability, once developed, allows children to learn specific segmental movements required to complete a task within an environmental context.

Orienting Under Load: Intrinsic Dynamics and Postural Affordances for Visual Perception

Orientation toward ones surroundings is necessary for prospective control of action, and constraints on orienting activity have consequences for animal survival. Physically coupled load is a constraint for humans wearing protective equipment (firefighters, soldiers, etc.). The consequences of load on postural affordances while transitioning to upright stance was used to quantify the impact of different soldier configurations. Eight participants established upright posture in 4 relevant load configurations (5.0 to 79.2 lb). Load affected the accessibility of optical information at a distance as evidenced by increasing downward head angles and reductions in postural coordination. Reductions in the variability of time to establish upright stance with load suggests a loss of functional adaptability. Load asymmetries played a significant role as the most asymmetric configuration (not the heaviest) had the most detrimental effect on postural affordances. Center of Pressure (CoP) dynamics reflected the consequences of asymmetric loading on postural regulation as greater power and fluctuations across frequencies were observed. Physically coupled load induces significant constraints on orienting activity, and load asymmetry contributes significantly to the detrimental effects of protective equipment on action-perception coupling during whole-body movements.

Movement dynamics and the environment to be perceived

In perception science, an alternative to focusing on individual sensory systems is to describe the environment to be perceived. We focus on the emergent dynamics of human-environment interactions as an important category of the environment to be perceived. We argue that information about such dynamics is available in subtle patterns of movement variability that, of necessity, stimulate multiple sensory systems.