Relative finger position influences whether you can localize tactile stimuli

To investigate whether the relative positions of the fingers influence tactile localization, participants were asked to localize tactile stimuli applied to their fingertips. We measured the location and rate of errors for three finger configurations: fingers stretched out and together so that they are touching each other, fingers stretched out and spread apart maximally and fingers stretched out with the two hands on top of each other so that the fingers are interwoven. When the fingers contact each other, it is likely that the error rate to the adjacent fingers will be higher than when the fingers are spread apart. In particular, we reasoned that localization would probably improve when the fingers are spread. We aimed at assessing whether such adjacency was measured in external coordinates (taking proprioception into account) or on the body (in skin coordinates). The results confirmed that the error rate was lower when the fingers were spread. However, there was no decrease in error rate to neighbouring fingertips in the fingers spread condition in comparison with the fingers together condition. In an additional experiment, we showed that the lower error rate when the fingers were spread was not related to the continuous tactile input from the neighbouring fingers when the fingers were together. The current results suggest that information from proprioception is taken into account in perceiving the location of a stimulus on one of the fingertips

The impetus theory in judgments about object motion: A new perspective

Several tendencies found in explicit judgments about object motion have been interpreted as evidence that people possess a naive theory of impetus. The theory states that objects that are caused to move by other objects acquire force that determines the kind of motion exhibited by the object, and that this force gradually dissipates over time. I argue that the findings can better be understood as manifestations of a general understanding of externally caused motion based on experiences of acting on objects. Experiences of acting on objects yield the idea that properties of the cause of motion are transmitted to the effect object. This idea functions as a heuristic for explicit predictions of object motion under conditions of uncertainty. This accounts not only for the findings taken as evidence for the impetus theory, but also for several findings that fall outside the scope of the impetus theory. It has also been claimed that judgments about the location at which a moving object disappeared are influenced by the impetus theory. I argue that these judgments are better explained in a different way, as best-guess extrapolations made by the visual system as a practical guide to interactions with the object, such as interception