**4.3.1 Application of results**

164 Virtual Reality and Environments

on motor planning. Future studies should examine kinematic findings at a deeper level to understand the use of vision in both open and closed loop functions. Additionally, since the treatment of visual contrast information by the CNS changes with time, as discussed in the next section, new studies must focus on delineating the role of such information for

While there are changes at the ocular level with age, the predominant cause of functional decline is due to a slowing of central processing in the brain (Chaput & Proteau, 1996; Inui, 1997; Light, 1990; Shields et al., 2005). The slowing of temporal processing has been specifically implicated in the decline of luminance contrast sensitivity in adults over 60. Motion sensitivity, which is dependent on contrast sensitivity, also declines with age (Spering et al., 2005; Trick & Silverman, 1991). Motion sensitivity is also known to be directly linked to function of dopaminergic circuitry, a system known to play a major role in the aging process (Wild-Wall et al., 2008). Despite these declines, older adults become more dependent on vision over time, resulting from the relative sparing of visual resources when compared to other sources of sensory feedback (Adamo et al., 2007; Chaput & Proteau, 1996; Goble et al., 2008; Lemay et al., 2004). The important concept to note is that this sparing of neurons in the visual systems results in a greater amount of substrate available for positive neuroplastic changes relating to motor output. Indeed, such positive changes have been documented in older adults when trained via the visual system to improve speed of processing (Ball, Edwards, & Ross, 2007; Edwards et al., 2005; Long & Rourke, 1989; Zhou et al., 2006). The key question to consider is how might this potential for plastic changes be manipulated and optimized? Given that the processing of luminance contrast information is linked in multiple ways with speed of processing, and speed of processing is a central theme in aging related functional decline, this visual property may be a useful means to answer the plasticity question. We believe a number of attributes of 3D VEs make them an ideal tool to aid in investigating this question, and believe design of VEs will directly benefit from the information gained. Therefore, we intend to investigate changes in sensorimotor processing of luminance contrast in older adults compared to younger adults. The information gained from this study will be directly applicable to development of technologies to rehabilitate

and enhance function in aging and neurologically compromised adults.

measures when compared to the moderate level for this group of participants.

Aim 1 is to test the hypothesis that luminance contrasts of target and limb have an effect on upper extremity kinematics in a virtual environment. This will be investigated using the methodology described previously with a reach to grasp paradigm. We will test a population of adults age 18-25 without history of visual or upper extremity sensorimotor dysfunction. We intend to study five contrast levels ranging from very low to very high. Based on previous studies of visual feedback, we believe that low levels of luminance contrast will negatively affect kinematic markers of upper extremity performance, for example slowed movement time, when compared to moderate and high levels. We also believe that high levels of contrast will not have a significant effect on performance

populations differing by age.

**4.3 Future research aims** 

**4.2 Aging and luminance contrast** 

We anticipate the results of this line of research will have implications in numerous fields. First, the information gained will have direct bearing on computer science for the userspecific design of next generation 3D virtual environments. As the world population continues to age, understanding of how to enhance performance with computer interfaces must take into account the physiologic changes that occur over time. Luminance contrast appears to be an important factor in upper extremity control, and one that is known to play a role in performance changes with age in natural environments. It stands to reason then that performance in a primarily visual environment, such as a 3D VE, will rely heavily on the neural processing of contrast. Secondly, we believe the field of rehabilitation will benefit indirectly through improvements in user-centered design. Currently, 3D VEs are regularly studied as a means to improve upon current practices in rehabilitation of patients poststroke. Unfortunately, one barrier to success continues to be usability and provision of costeffective, age-appropriate sensory feedback. Information on performance changes in older adults related to manipulation of luminance contrast may be of use to both program designers and rehab clinicians. For example, if older adults perform movements in VEs under certain contrast conditions in a manner equivalent to a natural environment, rehab clinicians may want to capitalize on such parameters to improve functional carryover of training to activities of daily living. Lastly, we believe results from our current and future study will contribute to the fields of gerontology and behavioural neuroscience by expanding our knowledge of visual processing and motor behaviour across the lifespan.
