Biomedical subjects

Allen Osman

Publications and source records attributed to Allen Osman.

5 recordsLinked to original sources

PubMed2006

The beat goes on: rhythmic modulation of cortical potentials by imagined tapping.

A frequency analysis was used to tag cortical activity from imagined rhythmic movements. Participants synchronized overt and imagined taps with brief visual stimuli presented at a constant rate, alternating between left and right index fingers. Brain potentials were recorded from across the scalp and topographic maps made of their power at the alternation frequency between left and right taps. Two prominent power foci occurred in each hemisphere for both overt and imagined taps, one over sensorimotor cortex and the other over posterior parietal cortex, with homologous foci in opposite hemispheres arising from oscillations 180 degrees out of phase. These findings demonstrate temporal isomorphism at a neural level between overt and imagined movements and illustrate a new approach to studying covert actions.

Brain Mapping↗

PubMed2005

Paradoxical lateralization of brain potentials during imagined foot movements.

Though each foot is controlled primarily by the contralateral hemisphere, the event-related brain potentials preceding an overt foot movement are largest over the ipsilateral side of the head. Because such "paradoxical lateralization" results from the spatial organization of the motor homunculus, it can provide a sign of motor-cortex activation. We report paradoxical lateralization in the potentials accompanying imagined foot movements, thereby demonstrating a contribution of cortical areas directly involved in movement execution.

Electroencephalography↗

PubMed2004

On the locus of speed-accuracy trade-off in reaction time: inferences from the lateralized readiness potential.

Lateralized readiness potentials (LRPs) were used to determine the stage(s) of reaction time (RT) responsible for speed-accuracy trade-offs (SATs). Speeded decisions based on several types of information were examined in 3 experiments, involving, respectively, a line discrimination task, lexical decisions, and an Erikson flanker task. Three levels of SAT were obtained in each experiment by adjusting response deadlines with an adaptive tracking algorithm. Speed stress affected the duration of RT stages both before and after the start of the LRP in all experiments. The latter effect cannot be explained by guessing strategies, by variations in response force, or as an indirect consequence of the pre-LRP effect. Contrary to most models, it suggests that SAT can occur at a late postdecisional stage.

Adult↗

PubMed2003

Temporal organization of covert motor processes during response selection and preparation.

Onset of a movement-related brain potential (lateralized readiness potential, LRP) was used to divide reaction time (RT) into two intervals: (1) stimulus onset to LRP onset, and (2) LRP onset to onset of the overt response. Effects on these intervals of advance information about the to-be-signaled response and of the mapping between fingers and response buttons were examined. These effects were used to reach conclusions about the organization of response preparation and about the identity of the processes influenced by advance information. In the absence of advance information, response preparation involved two steps. First, two of the four possible response alternatives were prepared, then one of these two was prepared further. Which pair of responses was prepared during the first step depended on the spatial arrangement of the fingers on the buttons, rather than on any common anatomical feature. Advance information about the upcoming response allowed the first step to be performed prior to the response signal, thus removing its contribution to RT. The second step, however, remained unaffected.

Arousal↗

PubMed2002

Linear spatial integration for single-trial detection in encephalography.

Conventional analysis of electroencephalography (EEG) and magnetoencephalography (MEG) often relies on averaging over multiple trials to extract statistically relevant differences between two or more experimental conditions. In this article we demonstrate single-trial detection by linearly integrating information over multiple spatially distributed sensors within a predefined time window. We report an average, single-trial discrimination performance of Az approximately 0.80 and faction correct between 0.70 and 0.80, across three distinct encephalographic data sets. We restrict our approach to linear integration, as it allows the computation of a spatial distribution of the discriminating component activity. In the present set of experiments the resulting component activity distributions are shown to correspond to the functional neuroanatomy consistent with the task (e.g., contralateral sensorymotor cortex and anterior cingulate). Our work demonstrates how a purely data-driven method for learning an optimal spatial weighting of encephalographic activity can be validated against the functional neuroanatomy.

Algorithms↗