SCAPPS location:London (Ontario, CA) date:16-18 October 2014
Aiming bias is influenced by the amount and type of visual information available when aiming to a visual illusion. The goal of the present experiment was to investigate whether vision would also mediate a proprioceptive illusion effect caused by muscle tendon vibration (TV) in young and older participants. Older participants have poorer proprioception and are more reliant on visual information. Thus, it was hypothesized that the illusion effects would be mediated by age-related factors. Visual information was gradually degraded from a situation in which the targets were present and participants made saccadic eye movements, to a condition in which the targets were not visible and participants were required to perform cyclical aiming while fixating a point between the two target positions. For young participants, TV induced an illusory reduction of 15% in movement amplitude. The effect was smaller when making saccades (37 mm reduction) than when fixating (30 mm). Apparently, extraretinal visual information reduced the proprioceptive illusion caused by TV. Interestingly, the primary saccade was also shortened by 3% when muscle TV was locally applied to the wrist. Older participants on average obtained a similar reduction due to TV (15.7%), but the impact of vision was greater (14.5 mm reduction in the saccade versus 42 mm in the fixation condition). Furthermore, the illusion correlated negatively with age, movement speed and fitness measures. The 42 mm illusion in fixation compared to 14 mm in saccade condition indicates that older participants are even more dependent on vision to suppress the illusion. The saccade amplitude was shortened by almost 5% in the no-target conditions. Overall, these results confirm a tight link and interaction between saccadic and manual perception and action. They highlight the flexibility of the visuo-manual control system based on the constraints posed by aging, the task demands and the available information.