How do we know what we are doing? Time, intention and awareness of action

Time is a fundamental dimension of consciousness. Many studies of the "sense of agency" have investigated whether we attribute actions to ourselves based on a conscious experience of intention occurring prior to action, or based on a reconstruction after the action itself has occurred. Here, we ask the same question about a lower level aspect of action experience, namely awareness of the detailed spatial form of a simple movement. Subjects reached for a target, which unpredictably jumped to the side on some trials. Participants (1) expressed their expectancy of a target shift during the upcoming movement, (2) pointed at the target as quickly and accurately as possible before returning to the start posiment to the target shift if required and (3) reproduced the spatial path of the movement they had just made, as accurately as possible, to give an indication of their awareness of the pointing movement. We analysed the spatial disparity between the initial and the reproduced movements on those with a target shift. A negative disparity value, or undershoot, suggests that motor awareness merely reflects a sluggish record of coordinated motor performance, while a positive value, or overshoot, suggests that participants' intention to point to the shifting target contributes more to their awareness of action than their actual pointing movement. Undershoot and overshoot thus measure the reconstructive (motoric) and the preconstuctive (intentional) aspects of action awareness, respectively. We found that trials on which subjects strongly expected a target shift showed greater overshoot and less undershoot than trials with lower expectancy. Conscious expectancy therefore strongly influences the experience of the detailed motor parameters of our actions. Further, a delay inserted either between the expectancy judgement and the pointing movement, or between the pointing movement and the reproduction of the movement, had no effect on visuomotor adjustment but strongly influenced action awareness. Delays during either interval boosted undershoots, suggesting increased reliance on a time-limited sensory memory for action. The experience of action is thus strongly influenced by prior thoughts and expectations, but only over a short time period. Thus, awareness of our actions is a dynamic and relatively flexible mixture of what we intend to do, and what our motor system actually does.     

Conscious intention and motor cognition

The subjective experience of conscious intention is a key component of our mental life. Philosophers studying 'conscious free will' have discussed whether conscious intentions could cause actions, but modern neuroscience rejects this idea of mind-body causation. Instead, recent findings suggest that the conscious experience of intending to act arises from preparation for action in frontal and parietal brain areas. Intentional actions also involve a strong sense of agency, a sense of controlling events in the external world. Both intention and agency result from the brain processes for predictive motor control, not merely from retrospective inference.     

Acquisition of a simple running response as a function of partial and continuous schedules of reinforcement

The Psychological Record -     

A low-cost system for measuring and analyzing human movement in three dimensions

This paper describes a system for measuring the three-dimensional movement of a point on the human body. The core components of the system are an ultrasonic computer mouse (The OWL), an IBM-compatible personal computer, and a suite of recording and analysis software written in National Instruments’ LabVIEW instrumentation programming language. The cost of these components is sufficiently low that we have been able to create a system for measuring human kinematics that is within the reach of a typical budget for student practical classes.     

Effects of frequency on visual word recognition tasks: where are they?

Compared the effect of frequency on lexical decision time (LDT) with that on reaction time (RT) in four other tasks, for the same words and subjects. Exp. 1 yielded an effect on semantic categorization RT (person vs. thing) similar in size and form to the effect on LDT. Exp. 2 yielded a substantial effect for syntactic categorization (noun vs. adjective), although weaker than the effect on LDT. In Exp. 3, the effect on naming RT for stress-final disyllabic words was identical to that on LDT, whereas the effect for stress-initial words was weaker. Exp. 4 showed no effect of frequency on delayed naming RT. The data undermine recent arguments for a (mainly) postidentification task-specific locus of frequency effects but are compatible with the older assumption (also characteristic of new PDP learning models) that lexical identification is a major locus of frequency effects (perhaps together with retrieval of meaning or phonology). But effects at that locus may be masked or diluted by other processes.     

Implicit body representations and the conscious body image

Recent studies have revealed that somatosensory processing relies on a class of implicit body representations showing large distortions of size and shape. The relation between these representations and the conscious body image remains unclear. Dissociations have been reported in the clinical literature on eating disorders between different body image measures, with larger and more consistent distortions found with depictive measures, in which participants compare their body to a visual depiction of a body, than metric measures, in which participants compare their body to some non-body standard. Here, we compared implicit body representations underlying position sense to the body image measured with both depictive and metric methods. The body image was measured using both a depictive method (template matching) in which participants judged whether their hand was wider or more slender than a shown hand picture, and a metric method (line length) in which participants judged whether different parts of their hand were shorter or longer than a presented line. Consistent with previous findings, characteristic distortions were found for the implicit body representation underlying position sense. These distortions were also found in attenuated form for metric - but not depictive - body image measures. While replicating the basic dissociation between implicit body representations and the conscious body image, these results demonstrate that this dissociation is not absolute and specific tasks may utilise both to varying degrees depending on task demands. Metric measures may not be pure measures of body image, but some combination of visual and somatosensory body representations.     

A 2.5-D representation of the human hand

Primary somatosensory maps in the brain represent the body as a discontinuous, fragmented set of two-dimensional (2-D) skin regions. We nevertheless experience our body as a coherent three-dimensional (3-D) volumetric object. The links between these different aspects of body representation, however, remain poorly understood. Perceiving the body's location in external space requires that immediate afferent signals from the periphery be combined with stored representations of body size and shape. At least for the back of the hand, this body representation is massively distorted, in a highly stereotyped manner. Here we test whether a common pattern of distortions applies to the entire hand as a 3-D object, or whether each 2-D skin surface has its own characteristic pattern of distortion. Participants judged the location in external space of landmark points on the dorsal and palmar surfaces of the hand. By analyzing the internal configuration of judgments, we produced implicit maps of each skin surface. Qualitatively similar distortions were observed in both cases. The distortions were correlated across participants, suggesting that the two surfaces are bound into a common underlying representation. The magnitude of distortion, however, was substantially smaller on the palmar surface, suggesting that this binding is incomplete. The implicit representation of the human hand may be a hybrid, intermediate between a 2-D representation of individual skin surfaces and a 3-D representation of the hand as a volumetric object.     

On the Hand Transport Component of Prehensile Movements

Jeannerod (1981) proposed that prehensile movements involve two independent visuomotor channels that are responsible for hand transport and hand aperture. In many studies, the movement of a marker placed on the wrist has been used as an index of hand transport because wrist movement is unaffected by the movements of the digits responsible for hand aperture. In the present study, the spatial paths of the wrist, index finger, and thumb of 5 adults, each performing 50 reaching movements, were measured with a WATSMART movement tracking system, and their variability was analyzed. The measures of movement variability suggest that the motor system is more concerned with thumb position than with wrist position during hand transport. Although the wrist is a technically convenient index of hand transport, the thumb may be a more appropriate index from the point of view of motor control.     

Experts see it all: configural effects in action observation

Biological motion perception is influenced by observers’ familiarity with the observed action. Here, we used classical dance as a means to investigate how visual and motor experience modulates perceptual mechanism for configural processing of actions. Although some ballet moves are performed by only one gender, male and female dancers train together and acquire visual knowledge of all ballet moves. Twenty-four expert ballet dancers (12 female) and matched non-expert participants viewed pairs of upright and inverted point light female and common dance movements. Visual discrimination between different exemplars of the same movement presented upright was significantly better in experts than controls, whilst no differences were found when the same stimuli were presented upside down. These results suggest expertise influences configural action processing. Within the expert group, effects were stronger for female participants than for males, whilst no differences were found between movement types. This observer gender effect could suggest an additional role for motor familiarity in action perception, over and above the visual experience. Our results are consistent with a specific motor contribution to configural processing of action.