[Delayed Copying of Unfamiliar Contour Shapes: Does Reaction Time Decrease with Growing Delay Reflect a Change in Internal Representation Of Fothcoming Movement?].

Abstract

Group of 24 adults has performed the delayed reproduction (copying) of unfamiliar contour shapes (trajectory templates). Templates were shown for 250 ms and the participants were asked to reproduce them upon detecting acoustical go signal (short click). Go signal was delayed relatively to the end of a visual template exposure by T = 0, 500, 1000, 2000 or 4000 ms. Block design of the experiment was used when delay T was held constant within a block consisted of 32 trials. We analyzed reaction time (RT), mean movement time (MT) along a single segment of trajectory, and the mean dwell time (DT) in the vertices of the template. It is shown that RT does not depend monotonically on the delay T showing a decrease at T ≤ 1000 ms and increase at T ≤ 2000 ms. The RT of T curve is well described by a simple additive model that includes a linearly growing and an exponentially decaying terms. The linear growth reflects the foreperiod effect, i.e., decreasing capacity to predict an exact moment of go signal with the growing delay T [Niemi, Naatanen, 1981; Meulenbroek, Van Galen, 1988]. We suggested that exponentially decaying term may be caused by the internal representation of a trajectory undergoing some transformation during retention in the working memory.