Motor simulation in tool-use effect on distance estimation: A replication of Witt and Proffitt (2008).

Witt and Proffit (Human Perception and Performance, 34 (6), 1479-1492, 2008) hypothesized that when people intend to reach a target, they run a motor simulation allowing them to anticipate potential reaching constraints and outcomes, which in turn affects spatial perception. They reported that participants estimated targets to be closer to them when they intended to use a reach-extending tool, but only when they did not perform a concurrent motor task. The authors concluded that the concurrent motor task prevented the simulation of tool-use and its effect on perception. Reported here is a replication that extends their work through an additional control group and a larger sample size. Our results failed to support either the role of motor simulation in the tool-use effect on distance estimation or the tool-use effect itself. Moreover, a reanalysis of Witt and Proffitt's data suggested that they should have been more nuanced in their own conclusions. Further replications are needed in order to elucidate the existence, nature, boundary conditions, and underlying mechanisms of the action constraint effects on space perception.

Mutual interferences between automatic ongoing spatial-updating with self-motion and source recall.

Recent models suggest that spatial updating of position with self-motion is a key component of remembering. In the first experiment, participants simultaneously performed a spatial task and a source recall. In the spatial task, blindfolded participants rotated to a new orientation and then pointed to an object's position. They pointed either from their new orientation (in the updating condition), or as if they were still in their starting orientation (in the ignoring condition). In the updating condition, participants had to accurately integrate their own movement whereas, in the ignoring condition, they had to ignore it. If spatial updating and episodic memory rely on the same network, only the updating condition should interfere with source recall. Results are in line with this prediction. A second experiment using a semantic memory task instead of source recall showed no interference effect. These results suggest that episodic memory and spatial updating are functionally linked.

Within reach but not so reachable: obstacles matter in visual perception of distances.

A large number of studies have shown that effort influences the visual perception of reaching distance. These studies have mainly focused on the effects of reach-relevant properties of the body and of the objects that people intend to reach. However, any influence of the reach-relevant properties of the surrounding environment remains still speculative. We investigated this topic in terms of the role of obstacle width in perceiving distances. Participants had to estimate the straight-line distance to a cylinder located just behind a transparent barrier of varying width. The results showed that participants perceived the straight-line distance to the cylinder as being longer when they intended to grasp the cylinder by reaching around a wide transparent barrier rather than by reaching around narrower ones. Interestingly, this effect might be due to the anticipated effort involved in reaching. Together, our results show that reach-relevant properties of the surrounding environment influence perceived distances, thereby supporting an embodied view of the visual perception of space.

A visual processing but no phonological disorder in a child with mixed dyslexia.

The case study of Martial, a French 9-year-old boy, who exhibits severe mixed dyslexia and surface dysgraphia is reported. Despite very poor pseudo-word reading, Martial has preserved phonological processing skills as his good oral language, good phoneme awareness and good verbal short-term memory show. He exhibited a strong length effect when reading briefly presented words but no sign of mini-neglect. His letter-string processing abilities were assessed through tasks of whole and partial report. In whole report, Martial could only name a few letters from briefly displayed 5-consonant strings. He showed an initial-position advantage and a sharper than expected left-to-right gradient of performance. He performed better when asked to report a single cued letter within the string but then showed an atypical right-side advantage. The same rightward attentional bias was observed in whole report when top-down control was prevented. Otherwise, Martial showed preserved single letter identification skills and good processing of 5-letter strings when letters were sequentially displayed one at a time. His poor letter-string processing thus reflects a parallel visual processing disorder that is compatible with either a visual attention (VA) span or a visual short-term memory disorder. Martial was further engaged in a complex reaching movement task involving VA and simultaneous processing. He performed motor sequences not as a whole but as a succession of independent motor units, suggesting that his attention was not allocated in parallel to the two to-be-reached targets prior to movement execution. Against a more basic motor disorder however, he showed good performance in a task of cyclical pointing movements. The overall findings suggest that Martial suffers from a visual simultaneous processing disorder that disturbs letter identification in strings. Instead of being restricted to letter-string processing, this VA disorder might extend to non-verbal task.

Ductus: a software package for the study of handwriting production.

Ductus is a software tool designed to analyze and aid understanding of the processes underlying handwriting production. Ductus is a digitizer-based device that provides online information on the handwriting process. It consists of two distinct modules that operate independently. The first module concerns stimulus presentation. It is particularly suited to experiments with children and patients presenting handwriting pathologies. The second module is devoted to data analysis. Apart from the geometrical aspects of handwriting, such as trajectory formation, Ductus provides a wide range of kinematic information, such as velocity, duration, fluency, and pauses, linked to the mastery of the movement itself. Ductus is available free from the authors. It works on a Windows platform with Wacom digitizers.