Speed discrimination and distance reproduction data.

Data related to the following publication:

Jan Churan, Johannes Paul, Steffen Klingenhoefer, Frank Bremmer (in press), Integration of visual and tactile information in reproduction of traveled distance. Journal of Neurophysiology. doi: 10.1152/jn.00342.2017

Description:

Speed discrimination

In the speed discrimination task, the subject was presented with a standard stimulus and a comparison stimulus (each 2 s long with a break of 500 ms in between). The standard stimulus was always presented first at a speed of either 3, 5 or 7 arbitrary units (AU)/s. The comparison stimulus was chosen from a range of +- 2 AU/s around the speed of the standard stimulus. After both stimuli had been presented, subjects had to indicate which one was perceived as faster by pressing one of two buttons. The combination of three standard speeds and two modality conditions resulted in 6 experimental conditions. In each condition 41 trials were performed that covered the given range of +- 2 AU/s in equidistant steps of 0.1 AU/s. In this discrimination task, each experimental condition was presented only once. The trials were conducted in a pseudo-randomized order.

Distance reproduction

In the first experiment, we tested the ability of the subjects to reproduce a previously passively observed traveled distance using visual, tactile or bi-modal feedback. The subject was presented with a simulation of self-motion over a certain distance. The speeds during this presentation were always constant at 4 or 7 AU/s and the distances were either 5, 10 or 15 AU. In this first phase the stimulation was always bi-modal. After this presentation and a brief pause of 500 ms the task of the subject was to reproduce the passively observed distance using a joystick. In this second part either only the visual information, only the tactile information, or both modalities were available. The order of all conditions was pseudo-random.

Re-scaling of tactile information

In the second experiment we investigated the effect of re-scaling of tactile information on the reproduced traveled distance. All simulated self-motion was bi-modal. The subjects were passively observing a simulated self-motion over a certain distance. The speed of this motion was not constant but had a sinusoidal profile with a peak speed at either 5 or 7 AU/s. The traveled distances were either 10, 15 or 20 AU. After the first presented distance and a brief gap of 500 ms another distance was presented passively. The speed profile of this second movement consisted of three different speeds between 3 AU/s and 10 AU/s. The distance covered by this second passive movement was always one third of the first passive distance but the subjects were neither informed about nor aware of this relationship. After the second presentation had stopped, the task of the subjects was to actively reproduce the first observed distance as a sum of the second passively observed distance and the subsequent active motion. In random 10% of the trials the tactile component of the motion was scaled up by 25% and in another 10% of the trials it was down-scaled by 25%. This means that the speed of the air flow on these trials was 25% faster (or slower) than in the rest of the trials. The re-scaling was applied only during the second passive motion and the active reproduction part of each trial. The subjects were not informed about and were not aware of this manipulation.

The experiments on distance reproduction and tactile rescaling were performed in two variations that differed in the relationship between the speed of the tactile stimulus and the speed of self-motion. While in the congruent condition the speed of the air flow was directly proportional to the speed of visual self-motion, in the incongruent condition the relation of the two measures was inversely proportional. The congruent and the incongruent configurations were always used in both, the presentation as well as in the reproduction phase of a trial. Importantly, a purely visual stimulation used in the two conditions was identical in both cases. The subjects were informed that in the incongruent experiments slow speed of air flow indicates a fast speed of self-motion. To avoid any confusion, separate groups of subjects were tested in the congruent and in the incongruent conditions.