Unifying the sensory and motor components of sensorimotor adaptation

Haith, A., Jackson, C.P.T., Miall, R.C. & Vijayakumar, S. (2008). NIPS 2008: 593-600.

Adaptation of visually guided reaching movements in novel visuomotor environments (e.g. wearing prism goggles) comprises not only motor adaptation but also substantial sensory adaptation, corresponding to shifts in the perceived spatial location of visual and proprioceptive cues. Previous computational models of the sensory component of visuomotor adaptation have assumed that it is driven purely by the discrepancy introduced between visual and proprioceptive estimates of hand position and is independent of any motor component of adaptation. We instead propose a unified model in which sensory and motor adaptation are jointly driven by optimal Bayesian estimation of the sensory and motor contributions to perceived errors. Our model is able to account for patterns of performance errors during visuomotor adaptation as well as the subsequent perceptual aftereffects. This unified model also makes the surprising prediction that force field adaptation will elicit similar perceptual shifts, even though there is never any discrepancy between visual and proprioceptive observations. We confirm this prediction with an experiment.

Sex differences in a virtual water maze: an eye tracking and pupillometry study

Mueller, S.C., Jackson, C.P.T. & Skelton, R.W. (2008). Behavioural Brain Research 193: 209-215.

Sex differences in human spatial navigation are well known. However, the exact strategies that males and females employ in order to navigate successfully around the environment are unclear. While some researchers propose that males prefer environment-centred (allocentric) and females prefer self-centred (egocentric) navigation, these findings have proved difficult to replicate. In the present study we examined eye movements and physiological measures of memory (pupillometry) in order to compare visual scanning of spatial orientation using a human virtual analogue of the Morris Water Maze task. Twelve women and twelve men (average age = 24 years) were trained on a visible platform and had to locate an invisible platform over a series of trials. On all but the first trial, participants’ eye movements were recorded for 3 s and they were asked to orient themselves in the environment. While the behavioural data replicated previous findings of improved spatial performance for males relative to females, distinct sex differences in eye movements were found. Males tended to explore consistently more space early on while females demonstrated initially longer fixation durations and increases in pupil diameter usually associated with memory processing. The eye movement data provides novel insight into differences in navigational strategies between the sexes.

A novel MR-compatible device for providing forces to the human finger during functional neuroimaging studies

Jackson, C.P.T., Bowtell, R., Morris, P.G. & Jackson, S.R. (2008). Neuroimage 40: 1731-1737.

Many motor learning experiments involve subjects performing a task while experiencing external force perturbations. However, it is difficult to transfer these tasks to functional magnetic resonance imaging (fMRI) studies, and much of the technology that currently exists to facilitate this is expensive to produce and difficult to use. Here, we report on the design and construction of a novel device (the ‘force coil’) that is simple and inexpensive, and that uses the static magnetic field inside the scanner to provide forces to the human finger. The coil incorporates a potentiometer in the base to allow the recording of angular position. To test whether the magnetic field generated by the current flowing through the coil would interfere with the functional images collected, we compared images from a phantom during the use of the coil at arm's length in a 7T magnet. There was no noticeable interference from the coil at the levels of current used in this experiment, which produced about 10 N of force in a 7T scanner. In conclusion, the force coil is a cheap, easy to operate device which provides forces to the finger inside the scanner without affecting image quality. Designs based on this principle are likely to prove useful in studies of motor learning using fMRI.

Contralateral manual compensation for velocity-dependent force perturbations

Jackson, C.P.T. & Miall, R.C. (2008). Experimental Brain Research 184: 261-267.

It is not yet clear how the temporal structure of a voluntary action is coded allowing coordinated bimanual responses. This study focuses on the adaptation to and compensation for a force profile presented to one stationary arm which is proportional to the velocity of the other moving arm. We hypothesised that subjects would exhibit predictive coordinative responses which would co-vary with the state of the moving arm. Our null hypothesis is that they develop a time-dependent template of forces appropriate to compensate for the imposed perturbation. Subjects were trained to make 500 ms duration reaching movements with their dominant right arm to a visual target. A force generated with a robotic arm that was proportional to the velocity of the moving arm and perpendicular to movement direction acted on their stationary left hand, either at the same time as the movement or delayed by 250 or 500 ms. Subjects rapidly learnt to minimise the final end-point error. In the delay conditions, the left hand moved in advance of the onset of the perturbing force. In test conditions with faster or slower movement of the right hand, the predictive actions of the left hand co-varied with movement speed. Compensation for movement-related forces appeared to be predictive but not based on an accurate force profile that was equal and opposite to the imposed perturbation.

Target selection: choice or response?

Jackson, C.P.T., Albert, N.B., Roberts, R.D., Galea, J.M. & Swait, G. (2007). Journal of Neuroscience 27: 6079-6080.