A ruler for measuring representational space.

In the last decade a number of theories have been formulated hypothesizing a "distortion" of representational space in neglect patients, in order to explain their impairment on tasks investigating the perception of horizontal extents. Trying to compensate for the relative lack of formalization in this field of research, a mathematical model of what a spatial distortion should be is formulated on the basis of theoretical considerations and of some neurophysiological evidence; furthermore, a psychophysical task is proposed that estimates the amount of distortion and is able to overcome some of the limits in the currently used methods. On this task, 32 normal subjects showed two different kinds of deviation from the ideal performance, neither of which is attributable to perceptual factors. Out of five neglect patients, two showed reliable distortion, another two showed a trend towards distortion (but in opposite directions with respect to one another), and one showed no sign of distortion. In conclusion, a new method for estimating distortion suggested that the explorative impairment--neglect--can dissociate from the metric one--distortion, as one would expect on grounds of a (evolutionarily plausible) separation between the two operations of exploring and measuring space. [ABSTRACT FROM AUTHOR]