EEG and MEG source imaging in duration/pitch comparison
N’Diaye K. (speaker), Garnero L., Pouthas V.
CNRS-UPR640 LENA, Paris, France
Recent years have seen a renewed interest in the study of time
perception in the range of sub-second durations. Even though a
distributed network of brain areas has been repeatedly evidenced in
timing tasks, little is known on the chronometry of their respective
involvement. To address this issue, we simultaneously recorded
electro- and magnetoencephalography (EEG / MEG) as human
participants were performing a duration comparison task (600/900
ms empty intervals marked by 20ms brief tones). Moreover, to
assess the specificity of the brain response towards timing-related
processes we contrasted this task with a non-temporal one (pitch
comparison) using the exact same set of stimuli. Delayed motor
selection and preparation was enforced by randomizing response
mapping. Topography and time-course of regional activity over the
cortical surface was reconstructed from scalp signals through
minimum L2-norm source estimation. Hit rates over 80% (without
significant differences between the two tasks) confirmed that
subjects selectively attended to the correct dimension. Both
encoding and comparison phases evoked slow potentials/fields
distinct from sensory evoked responses. Distributed source analysis
revealed an extended network of cortical areas involved at the
encoding stage (bilateral premotor cortex), at the comparison one
(right prefrontal) or in both (bilateral inferior parietal and superior
temporal gyrus). Although both tasks seemed to recruit common
areas, they differed in the distribution of activity within this
network as right frontal and bilateral parietal regions showed
stronger activity when the temporal dimension of a stimulus is to
be judged, especially at the comparison stage. The partial
interdimensional overlap of evoked responses supports the
hypothesis that timing tasks tap both unspecific processes (possibly
related to magnitude judgment in common with non-temporal
task) and more specific timing-related resources. Time-frequency
analyses are now being carried on to assess whether task-related
oscillatory responses might differentiate these two types of
processes.
Oral Communication #SS0306 at the IXth International Conference on Cognitive Neuroscience (ICON9), La Havana, Cuba, September 2005.