Dynamics of two psychomotor activities: linear aspects

Traditionally, variability in reaction time (RT) is usually interpreted as random error of measurement characterised as stochastic process. However, newer techniques (linear and nonlinear) have indicated that RT series may contain “hidden information” which is neither visually apparent, nor extractable with conventional methods of analysis. The aim of this study was to determine periodical changes in different psychomotor time series: complex reaction time (CRT) series and tapping intervals (TI) time series. A second aim was to examine whether the simultaneous performance of two psychomotor tasks showed interferention and as a result, changed the dynamical structure of underlying processes. Seven female subjects, aged between 19-25 participated in the experiment. There were five different experimental situations. The experimental design was 2x2 within groups factor experiment, which included 2 levels of CRT task difficulty and 2 task types (single task as well as dual task referring to simultaneous performance of CRT and tapping task). In addition, subjects performed a simple tapping task as alone. The results of this study indicated the existence of some dominant frequencies (periodical changes) in CRT series, as well as in TI time series. Those periodicities could be related to some characteristics of task performance and also, to the exercise and rhythm of breathing. On the other hand, the results of spectral analysis indicated that those time series were not stationary. There was no match found between dominant frequencies in different time segments of CRT and TI time series, which implies difficulties in result interpretation. However, Gilden et al. (1995) suggested that characteristics of 1/f spectrum could provide much more relevant information than conventional spectral analysis parameters (differentiation of cognitive component and motor component). The results of this study partly agreed with those of Gilden et al., in that the 1/f slopes were non-zero and negative. 1/f spectrum appears to have two components, a flat, white noise component for the high frequencies (motor component), and a negative slope for the low frequencies (cognitive component). Those slopes also depended on the task difficulty. Finally, the results have showed that dynamical structure (linear aspects) of CRT time series didn’t change during the simultaneous performance of two psychomotor tasks, while dynamical structure of TI time series changed significantly