1: Motor Control. 2004 Oct;8(4):534-46. 

Learning multiple visuomotor transformations: adaptation and context-dependent
recall.

Mistry S, Contreras-Vidal JL.

Cognitive-Motor Neuroscience laboratory, Dept of Kinesiology, University of
Maryland, Colleg Park, MD 20742-2611, USA.

Recent motor control theories suggest that the brain uses internal models to
plan and control accurate movements. An internal model is thought to represent
how the biomechanics of the arm interacting with the outside world would respond
to a motor command; therefore it can be seen as a predictive model of the
reafference that helps the system plan ahead. Moreover, adaptation studies show
that humans can learn multiple internal models. It is not clear, however,
whether and how contextual cues are used to switch among competing internal
models, which are required to compensate for altered environments. To
investigate this question, we asked healthy participants to perform center-out
pointing movements under normal and distorted visual feedback (0 degrees , 30
degrees counterclockwise, and 60 degrees clockwise rotation of hand-screen
cursor relationships) conditions. The results suggest that humans can learn
multiple environments simultaneously and can use contextual cues to facilitate
adaptation and to recall the appropriate internal model of the visuomotor
transformation.

PMID: 15585906 [PubMed - indexed for MEDLINE]



2: Nat Neurosci. 2004 Dec;7(12):1370-5. Epub 2004 Nov 21. 

Erratum in:
    Nat Neurosci. 2005 Jan;8(1):121.

Comment in:
    Nat Neurosci. 2004 Dec;7(12):1285-7.

Human anterior cingulate neurons and the integration of monetary reward with
motor responses.

Williams ZM, Bush G, Rauch SL, Cosgrove GR, Eskandar EN.

Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical
School, Boston, Massachusetts 02114, USA.

The human dorsal anterior cingulate cortex (dACC) has been implicated in
cognitive processes that have been proposed to play a role in integrating
contextual information needed to select or modify appropriate motor responses.
In humans, however, there has been little direct evidence tying the dACC to the
integration of contextual information and behavioral response. We used
single-neuron recordings from human subjects to evaluate the role of the dACC in
reward-based decision making. Subjects undergoing planned surgical cingulotomy
performed a task where they were instructed to make specific movements in
response to changing monetary rewards. In many neurons, activity increased in
response to a diminished reward, and was also predictive of the movement
ultimately made. After dACC ablation, subjects made selectively more errors when
they were required to change movement based on reward reduction. These findings
suggest that the dACC in humans plays an important role in linking
reward-related information with alternative actions.

PMID: 15558064 [PubMed - indexed for MEDLINE]



3: PLoS Biol. 2004 Oct;2(10):e330. Epub 2004 Sep 21. 

A neuroeconomics approach to inferring utility functions in sensorimotor
control.

Kording KP, Fukunaga I, Howard IS, Ingram JN, Wolpert DM.

Sobell Department of Motor Neuroscience, Institute of Neurology, University
College London, London, United Kingdom. konrad@koerding.de

Making choices is a fundamental aspect of human life. For over a century
experimental economists have characterized the decisions people make based on
the concept of a utility function. This function increases with increasing
desirability of the outcome, and people are assumed to make decisions so as to
maximize utility. When utility depends on several variables, indifference curves
arise that represent outcomes with identical utility that are therefore equally
desirable. Whereas in economics utility is studied in terms of goods and
services, the sensorimotor system may also have utility functions defining the
desirability of various outcomes. Here, we investigate the indifference curves
when subjects experience forces of varying magnitude and duration. Using a
two-alternative forced-choice paradigm, in which subjects chose between
different magnitude-duration profiles, we inferred the indifference curves and
the utility function. Such a utility function defines, for example, whether
subjects prefer to lift a 4-kg weight for 30 s or a 1-kg weight for a minute.
The measured utility function depends nonlinearly on the force magnitude and
duration and was remarkably conserved across subjects. This suggests that the
utility function, a central concept in economics, may be applicable to the study
of sensorimotor control.

PMID: 15383835 [PubMed - in process]



4: PLoS Biol. 2004 Nov;2(11):e364. Epub 2004 Oct 26. 

Perception, action, and Roelofs effect: a mere illusion of dissociation.

Dassonville P, Bala JK.

Department of Psychology and Institute of Neuroscience, University of Oregon,
Eugene, Oregon, USA. prd@darkwing.uoregon.edu

A prominent and influential hypothesis of vision suggests the existence of two
separate visual systems within the brain, one creating our perception of the
world and another guiding our actions within it. The induced Roelofs effect has
been described as providing strong evidence for this perception/action
dissociation: When a small visual target is surrounded by a large frame
positioned so that the frame's center is offset from the observer's midline, the
perceived location of the target is shifted in the direction opposite the
frame's offset. In spite of this perceptual mislocalization, however, the
observer can accurately guide movements to the target location. Thus, perception
is prone to the illusion while actions seem immune. Here we demonstrate that the
Roelofs illusion is caused by a frame-induced transient distortion of the
observer's apparent midline. We further demonstrate that actions guided to
targets within this same distorted egocentric reference frame are fully expected
to be accurate, since the errors of target localization will exactly cancel the
errors of motor guidance. These findings provide a mechanistic explanation for
the various perceptual and motor effects of the induced Roelofs illusion without
requiring the existence of separate neural systems for perception and action.
Given this, the behavioral dissociation that accompanies the Roelofs effect
cannot be considered evidence of a dissociation of perception and action. This
indicates a general need to re-evaluate the broad class of evidence purported to
support this hypothesized dissociation.

PMID: 15510224 [PubMed - in process]