Torques do not influence proprioceptive localization of the hand.

Because muscle torques counteracting gravity vary systematically during a movement of the arm, it has been suggested that torque differences that occur during a movement provide important information for judging the distance moved away from the body. To test this suggestion, we examined whether external vertical forces applied to the hand (and the torque differences due to these forces) influence proprioception. In a first experiment, the added vertical forces were constant, resulting in a change in torque that was proportional to the gravitational torque, as when holding an object in your hand. This did not affect proprioception. In a second experiment, gradient force fields were used to dramatically change the torque differences. Again, no effect on proprioception was found. Thus, vertical forces caused by hand-held objects do not play an important role in judging the position or movement of the hand.

Effects of stimulus duration on audio-visual synchrony perception.

The integration of visual and auditory inputs in the human brain occurs only if the components are perceived in temporal proximity, that is, when the intermodal time difference falls within the so-called subjective synchrony range. We used the midpoint of this range to estimate the point of subjective simultaneity (PSS). We measured the PSS for audio-visual (AV) stimuli in a synchrony judgment task, in which subjects had to judge a given AV stimulus using three response categories (audio first, synchronous, video first). The relevant stimulus manipulation was the duration of the auditory and visual components. Results for unimodal auditory and visual stimuli have shown that the perceived onset shifts to relatively later positions with increasing stimulus duration. These unimodal shifts should be reflected in changing PSS values, when AV stimuli with different durations of the auditory and visual components are used. The results for 17 subjects showed indeed a significant shift of the PSS for different duration combinations of the stimulus components. Because the shifts were approximately equal for duration changes in either of the components, no net shift of the PSS was observed as long as the durations of the two components were equal. This result indicates the need to appropriately account for unimodal timing effects when quantifying intermodal synchrony perception.