Stiffness as a control variable in motor performance

In the experiments described in this article we investigated the control of stiffness of the effector system in relation to parameters of the movement. If the velocity of a movement is chosen, it appears that at the same time the stiffness of the effector system is set to a preferred value. By changing the instruction given to the subject it is possible to change the relationship between velocity and stiffness without changing the kinematic parameters of the movement.Finally, the changes of stiffness and velocity in a learning process are studied. In conformity with what might be expected on intuitive grounds, it is found that velocity increases spontaneously during learning while stiffness decreases. The results are discussed in connection with the generation of motor programmes.     

Effects of visual-field and matching instruction on event-related potentials and reaction time

Vertical letter pairs were presented randomly in the left and right visual hemifields in a physical identity match and name identity match condition. The reaction times showed a right visual field superiority for name matches, and a left visual field superiority for physical matches. Event-related potentials to letter pairs showed a sequence of three waves: a negative wave (N2, around 270 msec), a positive wave (P3, around 500 msec), and a broad positive slow wave (SW, around 600-700 msec), respectively. P3 and SW amplitudes were consistently larger at the left hemisphere than at the right hemisphere, regardless of the field of stimulation. At both hemispheres, N2 waves were always larger to stimuli presented in the visual field contralateral to a hemisphere than stimuli presented in the visual field ipsilateral to a hemisphere. The positive waves (P3, SW) showed the opposite pattern: smaller amplitudes to stimuli that were presented contralaterally than stimuli that were presented ipsilaterally to a given hemisphere. These results were attributed to a shift in sustained negativity on the directly stimulated hemisphere, relative to the indirectly stimulated hemisphere, reflecting either sensory at attentional processes in the posterior cerebral hemispheres.     

The variety of consequence,according to Bolzano

Contemporary historians of logic tend to credit Bernard Bolzano with the invention of the semantic notion, of consequence, a full century before Tarski. Nevertheless, Bolzano's work played no significant rôle in the genesis of modern logical semantics. The purpose of this paper is to point out three highly original, and still quite relevant themes in Bolzano's work, being a systematic study of possible types of inference, of consistency, as well as their meta-theory. There are certain analogies with Tarski's concerns here, although the main thrust seems to be different, both philosophically and technically. Thus, if only obliquely, we also provide some additional historical perspective on Tarski's achievement.     

Global-local orientation congruency effects in visual search

In a visual search task, subjects had to decide which of 2 possible target letters was presented among 12 distractor letters. The 13 characters were arranged to form a global Navon-type letter. The global letter and the local letters (target and distractors) were independently presented in four different viewer-related orientations. When the global letter and the target were frequently congruently oriented, the response times increased with growing orientation disparity between them. This global-target congruency effect was independent from target identity (Experiment 1), and it diminished when global and target orientations were not correlated (Experiment 2). The results indicate that the orientation of the global letter can be deliberately used in order to facilitate the processing of congruently oriented local targets. The alignment of a spatial frame of reference is discussed as the most probable process underlying this facilitation.