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According to the schema theory, variability during practice allows for a larger repertoire of movements to help form a generalized motor program for similar motor skills. Varied training is thought to enhance long-term retention of the motor program due to the heightened difficulty presented. In a highly cited study on this topic, Kerr and Booth (Perceptual and Motor Skills 46 (1978), 395-401) trained two groups of children for 10weeks to throw a beanbag towards either one central target (specific group) or two targets that were ±1 foot away from the central target (varied group). They found that the varied group performed significantly better than the specific group when both groups were tested at the central target. We, following the same paradigm, trained 30 adults on a similar beanbag throwing task and tested them at various target distances. Our results suggested that after 5-7weeks of training, the specific groups tended to undershoot at longer distances and overshoot at shorter distances while the varied group tended to center their throws around the target at all distances. However, the overall magnitude of error (regardless of over- or undershooting) was similar across groups. We found some support for the hypothesis that the varied group could better generalize to untrained distances, but this advantage was found mainly for the longest distance and disappeared by a posttest held two weeks after practice.

Visual perception is an important component of environmental navigation. Previous research has revealed large individual differences in navigational strategies (i.e., the body's kinesthetic and embodied approach to movement) and the perception of environmental surfaces (via distance estimations), but little research has investigated the potential relationship between these sources of individual variation. An important navigational strategy is the interaction between reliance on visual cues and vestibular or proprioceptive cues. We investigated the role of this navigational strategy in the perception of environmental surfaces. The results supported three embodied evolutionary predictions: Individuals who were most reliant on visual context (1) overestimated vertical surfaces significantly more, and (2) feared falling significantly more, than did those who were least reliant on visual context; and (3) all individuals had roughly accurate horizontal distance estimates, regardless of their navigational strategy. These are among the first data to suggest that individual differences in perception are closely related to the individual differences in navigation that derive from navigational risks. Variable navigational strategies may reflect variable capacities to perceive and navigate the environment.

Most behaviors are conditional upon successful navigation of the environment, which depends upon distance perception learned over repeated trials. Unfortunately, we understand little about how learning affects distance perception–especially in the most common human navigational scenario, that of adult navigation in familiar environments. Further, dominant theories predict mutually exclusive effects of learning on distance perception, especially when the risks or costs of navigation differ. We tested these competing predictions in four experiments in which we also presented evolutionarily relevant navigation costs. Methods included within- and between-subjects comparisons and longitudinal designs in laboratory and real-world settings. Data suggested that adult distance estimation rapidly reflects evolutionarily relevant navigation costs and repeated exposure does little to change this. Human distance perception may have evolved to reflect navigation costs quickly and reliably in order to provide a stable signal to other behaviors and with little regard for objective accuracy.

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