Aaron Fath

Static and dynamic visual information about the size and passability of an aperture

The role of static eyeheight-scaled information in perceiving the passability of and guiding locomotion through apertures is well established. However, eyeheight-scaled information is not the only source of visual information about size and passability. In this study we tested the sufficiency of two other sources of information, both of which are available only to moving observers (ie are dynamic) and specify aperture size in intrinsic body-scaled units. The experiment was conducted in an immersive virtual environment that was monocularly viewed through a head-mounted display. Subjects walked through narrow openings between obstacles, rotating their shoulders as necessary, while head and shoulder position were tracked. The task was performed in three virtual environments that differed in terms of the availability of eyeheight-scaled information and the two dynamic sources of information. Analyses focused on the timing and amplitude of shoulder rotation as subjects walked through apertures, as well as walking speed and the number of collisions. Subjects successfully timed and appropriately scaled the amplitude of shoulder rotation to fit through apertures in all three conditions. These findings suggest that visual information other than eyeheight-scaled information can be used to guide locomotion through apertures.

Training Compliance Control Yields Improvements in Drawing as a Function of Beery Scores

Many children have difficulty producing movements well enough to improve in sensori-motor learning. Previously, we developed a training method that supports active movement generation to allow improvement at a 3D tracing task requiring good compliance control. Here, we tested 7–8 year old children from several 2nd grade classrooms to determine whether 3D tracing performance could be predicted using the Beery VMI. We also examined whether 3D tracing training lead to improvements in drawing. Baseline testing included Beery, a drawing task on a tablet computer, and 3D tracing. We found that baseline performance in 3D tracing and drawing co-varied with the visual perception (VP) component of the Beery. Differences in 3D tracing between children scoring low versus high on the Beery VP replicated differences previously found between children with and without motor impairments, as did post-training performance that eliminated these differences. Drawing improved as a result of training in the 3D tracing task. The training method improved drawing and reduced differences predicted by Beery scores.

Training to improve manual control in 7–8 and 10–12 year old children: Training eliminates performance differences between ages

Many children have difficulty producing movements well enough to improve in perceptuo-motor learning. We have developed a training method that supports active movement generation to allow improvement in a 3D tracing task requiring good compliance control. We previously tested 7-8 year old children who exhibited poor performance and performance differences before training. After training, performance was significantly improved and performance differences were eliminated. According to the Dynamic Systems Theory of development, appropriate support can enable younger children to acquire the ability to perform like older children. In the present study, we compared 7-8 and 10-12 year old school children and predicted that younger children would show reduced performance that was nonetheless amenable to training. Indeed, the pre-training performance of the 7-8 year olds was worse than that of the 10-12 year olds, but post-training performance was equally good for both groups. This was similar to previous results found using this training method for children with DCD and age-matched typically developing children. We also found in a previous study of 7-8 year old school children that training in the 3D tracing task transferred to a 2D drawing task. We now found similar transfer for the 10-12 year olds.

A geometric and dynamic affordance model of reaches-to-grasp: Men take greater risks than women.

Mon-Williams and Bingham (2011) developed an affordance model of the spatial structure of reaches-to-grasp. With a single free parameter (P), the model predicted the safety margins (SMs) exhibited in maximum grasp apertures (MGAs), during the approach of a hand to a target object, as a function of an affordance measure of object size and a functional measure of hand size. An affordance analysis revealed that object size is determined by a diagonal through the object, called the maximum object extent. Mon-Williams and Bingham provided no theoretical account for the empirically determined values of P. We now address this question. Snapp-Childs and Bingham (2009) augmented Warrens (1984) geometric affordance scaling model with a dynamical component determined by the stability of the motor performance. Because P was found to vary with the speeds of reaches, we incorporated a measure of the variability of performance into the model to yield predictions of P. We also found that P varied with gender. In respect to the size of safety margins, women were more conservative in taking risks then men. Finally, following Warren (1984), the classic paradigm for testing affordance models is to test the scaling relations with both small and large participants. We tested small- and large-handed men and small- and large-handed women and found that the new parameter free model successfully accounted for the spatial structure of reaches-to-grasp.

Training children aged 5–10 years in compliance control: tracing smaller figures yields better learning not specific to the scale of drawn figures

Previously we developed a method that supports active movement generation to allow practice with improvement of good compliance control in tracing and drawing. We showed that the method allowed children with motor impairments to improve at a 3D tracing task to become as proficient as typically developing children and that the training improved 2D figure copying. In this study, we expanded the training protocol to include a wider variety of ages (5–10-year-olds) and we made the figures traced in training the same as in figure copying, but varied the scale of training and copying figures to assess the generality of learning. Forty-eight children were assigned to groups trained using large or small figures. All were tested before training with a tracing task and a copying task. Then, the children trained over five sessions in the tracing task with either small or large figures. Finally, the tracing and copying tasks were tested again following training. A mean speed measure was used to control for path length variations in the timed task. Performance on both tasks at both baseline and posttest varied as a function of the size of the figure and age. In addition, tracing performance also varied with the level of support. In particular, speeds were higher with more support, larger figures and older children. After training, performance improved. Speeds increased. In tracing, performance improved more for large figures traced by children who trained on large figures. In copying, however, performance only improved significantly for children who had trained on small figures and it improved equally for large and small figures. In conclusion, training by tracing smaller figures yielded better learning that was not, however, specific to the scale of drawn figures. Small figures exhibit greater mean curvature. We infer that it yielded better general improvement.

Binocular Perception of 2D Lateral Motion and Guidance of Coordinated Motor Behavior.

Zannoli, Cass, Alais, and Mamassian (2012) found greater audiovisual lag between a tone and disparity-defined stimuli moving laterally (90–170 ms) than for disparity-defined stimuli moving in depth or luminance-defined stimuli moving laterally or in depth (50–60 ms). We tested if this increased lag presents an impediment to visually guided coordination with laterally moving objects. Participants used a joystick to move a virtual object in several constant relative phases with a laterally oscillating stimulus. Both the participant-controlled object and the target object were presented using a disparity-defined display that yielded information through changes in disparity over time (CDOT) or using a luminance-defined display that additionally provided information through monocular motion and interocular velocity differences (IOVD). Performance was comparable for both disparity-defined and luminance-defined displays in all relative phases. This suggests that, despite lag, perception of lateral motion through CDOT is generally sufficient to guide coordinated motor behavior.

Comparison of monocular and stereo sources of motion information about time-to-contact of slow and fast objects

Stereomotion perception relies on two primary sources of information: interocular velocity differences (IOVD) and changes in disparity over time (CDOT). IOVD results from comparison of two monocular flow fields (MFF). Binocular disparity results from comparison of two monocular image structures and CDOT characterizes how this disparity evolves. CDOT-based stereomotion perception has been theorized to be a slower process than IOVD-based perception. If so, CDOT should be an inferior source of information for fast-moving objects. If CDOT is inferior for fast objects, is there a spatiotemporal domain in which CDOT is superior? Ten participants were each presented with three types of displays that depicted two squares approaching from different distances in depth at different constant velocities yielding different times-to-contact (TTC). Squares disappeared during approach and participants specified which square would have contacted them first. One display type was dynamic random-dot stereograms that isolated CDOT by rerandomizing points each frame (CDOT-only). Another was evolving (i.e., without rerandomization) random-dot configurations (MFF+IOVD). Corresponding points were not used, as they are in stereograms, so disparity did not specify approach. The third was evolving random-dot stereograms, so motion was defined by MFF, IOVD, and CDOT (COMBINED). For all three displays, in half of the trials, the two squares moved at speeds ranging 26-32 cm/s. In the other half, speeds ranged 73-127 cm/s. For fast stimuli, performance as measured by proportion correct was comparable for MFF+IOVD and COMBINED trials, but CDOT-only trials were significantly worse. Performance with slow stimuli was comparable for CDOT-only and COMBINED trials, but MFF+IOVD trials were significantly worse. Optimal performance levels were similar for both speed conditions. To yield invariant performance levels across speeds, the visual system appears to use primarily CDOT to perceive motion of slower objects, but MFF and IOVD for faster objects. Meeting abstract presented at VSS 2015.

Training of compliance control across different scales of movement yields general learning in children

INTRODUCTION Previously we (Snapp-Childs et al., 2013a; 2013b; 2014) developed a method that supports active movement generation to allow practice with improvement of good compliance control. We showed that the method allowed children with Developmental Coordination Disorder to improve at a 3D tracing task to become as proficient as Typically Developing children who had also trained. We also showed that the training improved figure copying. In this study, we expanded the training protocol to include a wider variety of ages (5-10 year olds) and we varied the scale of training (smaller or larger figures of the same shape) to assess the generality of learning. METHODS Fifty children (eighteen 5-6 year olds, sixteen 7-8 year olds, and sixteen 9-10 year olds) were tested with the Beery VMI, the 3D tracing task, and a 2D letter-like figure-copying task. The children then trained on one version of the 3D tracing task (smaller or larger scale figures) until they all reached comparably good proficiency. The 3D tracing and copying tasks were tested again following training. RESULTS Performance on the 3D tracing task at baseline varied as a function of the level of difficulty, size of figure, and age. After training, the age differences were eliminated but the level of difficulty and size effects remained although the differences were greatly reduced. Also, training (on small versus larger figures) now influenced performance: training with small figures gave an advantage on smaller figures, while training with large figures gave an advantage on larger figures. CONCLUSIONS Training on the 3D tracing task, whether with larger or smaller scale figures, greatly improved performance and eliminated age differences but yielded some training specific effects. In conclusion, the training method does yield general learning and is not highly specific to one particular age group. Meeting abstract presented at VSS 2015.

Eye-hand coordination strategies in older adults

Hand movement kinematics and eye-hand coordination are affected by aging. These age differences are exacerbated when task difficulty is increased, but the exact nature of these differences has yet to be established. We examined the performance of 12 older adults (mean age = 74) and 11 younger adults (mean age = 20) on a multi-phase prehension task. Participants had to reach for and pick up a target object with their preferred hand, place it in a tray, then reach for a second target object and place that in the same tray (baseline condition). On half the trials (stabilising condition) participants were required to hold the tray as still as possible just above the surface of the table with their non-preferred hand. Hand and eye movements were recorded. Older adults took longer to complete their overall movement but only in the stabilising condition [t(21) = 3.38 ; p < 0.01], largely due to an extended duration for the first submovement. They reached lower peak velocities and spent proportionally less time decelerating than the younger adults. Group differences were most apparent at the start of the movement and in the stabilising condition, suggesting both that older adults look more like their younger counterparts if given enough time, and that the added complexity of the stabilising task had a greater effect on the performance of the older adults than the young. Older adults adopted two different eye-hand coordination strategies, preferring to make an eye movement to the next target as soon as possible in some circumstances, or spending longer fixating the current target when accuracy requirements were high. Older adults appeared to employ an eye movement strategy that enabled them to benefit from visual feedback, presumably to aid hand movement control and improve task performance. Meeting abstract presented at VSS 2015.