Scheduled for Research Consortium Measurement, Exercise Physiology and Motor Behavior Poster Session, Friday, April 28, 2006, 8:45 AM - 10:15 AM, Convention Center: Exhibit Hall Poster Area I


Does Target Viewing Time Influence Perceived Reachability?

Carl Gabbard and Diala Ammar, Texas A&M University-College Station, College Station, TX

Reaching action requires a complex set of perceptual to motor transformations. One of the initial steps is to derive a perceptual estimate of the object's distance and location relative to the body. Although a considerable body of evidence suggests that we are very accurate at estimating reaching distances, even from childhood, other reports confirm a range of error. One of the most common findings in actual versus imagined (perceived) experiments is the observation of an overestimation bias at midline positions. Of the studies reviewed, target (object) viewing time has received minimal if any attention. The present study examined the influence of target viewing time on perceived reachability in a 1-df workspace. Right-handed subjects (N = 29) were asked to judge the simulated reachability of midline targets using their dominant limb in viewing conditions of 150ms, 500ms, 1s and 2s. Seven targets (2 cm circles) were presented in each condition – three above (distal) and three below (proximal) actual reach. Stimulus presentation was given in random order with subjects receiving five trials at each of the seven sites. Responses were compared to actual maximum reach. In reference to percent error, the150 ms condition revealed the least error at proximal targets and the most inaccuracy with distal stimuli. This condition was also distinct with a significant overestimation bias – a common observation in earlier studies. However, with increasing viewing time this bias was reduced. These data provide evidence that 150 ms is effective for estimating reach within one's general 1-df peripersonal workspace. However, with judgments distal from that point, more time enhanced accuracy, with 500 ms and 1 s being optimal. Overall results are discussed relative to perceptual effectiveness in programming reaching movements.
Keyword(s): research

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