Contemporary research clearly indicates that visual information and an action representation of that data are critical factors in planning reach movements. In that process, theory suggests that individuals use vision-for-perception and vision-for-action (Goodale et al., 2005, 2008). Our intent was to gain insight to the development of these systems in the context of estimating reach distance within an egocentric frame of reference; a process that provides a window to the cognitive level of action planning.
Method
Children (n = 66) ages 5- to 11-years and adults (n = 17) estimated reach distance via motor imagery in immediate (visually-guided) (0 delay) and response-delay (memory-guided -1 s, 2 s, and 4 s) conditions. According to the idea of visual-for-perception and vision-for-action, visuomotor processes responsible for action control retain information in real-time about the target. Therefore, our assumption was that at some point, delay should have an adverse affect on performance. Actual maximum reach was compared to estimates in multiple locations in peripersonal (with reach) and extrapersonal space (out of reach). Conditions were counterbalanced - each with 7 target distances randomly presented with 3 trials per target.
Analysis/Results
Group x Condition x Space ANOVA results for accuracy indicated that introducing a delay, specifically a ≥ 2s delay, affected responses in all age groups, especially the 5- and 7-year-olds, p < .01. In regard to the direction of error, target distribution data and mean bias analysis indicated that as delay increased, children as a group tended to overestimate, whereas adults underestimated. With reference to Space, there were no differences between conditions in peripersonal space; however, children overall were less accurate in extrapersonal space; once again the 5- and 7-year-olds were more effected by delay.
Conclusions
Obviously, visual information and an action representation are critical factors in planning reach movements. These findings indicate that children as young as 5 years of age are capable of using egocentric cues via dorsal stream to make functional judgments of reachability in peripersonal space with minimal delay; however, as delay increases (≥ 2 s), errors increase. In addition to the developmental outcome, these findings appear to support the two-visual-system hypothesis and implications of how each system works together to plan and execute action.
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