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Scalp Distribution (scalp + distribution)

Distribution by Scientific Domains

Psychology	80%

Selected Abstracts

Early neural activity in Necker-cube reversal: Evidence for low-level processing of a gestalt phenomenon

PSYCHOPHYSIOLOGY, Issue 1 2004
Jürgen Kornmeier
Abstract Normally we experience the visual world as stable. Ambiguous figures provide a fascinating exception: On prolonged inspection, the "Necker cube" undergoes a sudden, unavoidable reversal of its perceived front-back orientation. What happens in the brain when spontaneously switching between these equally likely interpretations? Does neural processing differ between an endogenously perceived reversal of a physically unchanged ambiguous stimulus and an exogenously caused reversal of an unambiguous stimulus? A refined EEG paradigm to measure such endogenous events uncovered an early electrophysiological correlate of this spontaneous reversal, a negativity beginning at 160 ms. Comparing across nine electrode locations suggests that this component originates in early visual areas. An EEG component of similar shape and scalp distribution, but 50 ms earlier, was evoked by an external reversal of unambiguous figures. Perceptual disambiguation seems to be accomplished by the same structures that represent objects per se, and to occur early in the visual stream. This suggests that low-level mechanisms play a crucial role in resolving perceptual ambiguity. [source]

Neural sensitivity to human voices: ERP evidence of task and attentional influences

PSYCHOPHYSIOLOGY, Issue 2 2003
Daniel A. Levy
Abstract In an earlier study, we found that human voices evoked a positive event-related potential (ERP) peaking at ,320 ms after stimulus onset, distinctive from those elicited by instrumental tones. Here we show that though similar in latency to the Novelty P3, this Voice-Sensitive Response (VSR) differs in antecedent conditions and scalp distribution. Furthermore, when participants were not attending to stimuli, the response to voices was undistinguished from other harmonic stimuli (strings, winds, and brass). During a task requiring attending to a feature other than timbre, voices were not distinguished from voicelike stimuli (strings), but were distinguished from other harmonic stimuli. We suggest that the component elicited by voices and similar sounds reflects the allocation of attention on the basis of stimulus significance (as opposed to novelty), and propose an explanation of the task and attentional factors that contribute to the effect. [source]

Neural Correlates of Children's Theory of Mind Development

CHILD DEVELOPMENT, Issue 2 2009
David Liu
Young children show significant changes in their mental-state understanding as marked by their performance on false-belief tasks. This study provides evidence for activity in the prefrontal cortex associated with the development of this ability. Event-related brain potentials (ERPs) were recorded as adults (N = 24) and 4-, 5-, and 6-year-old children (N = 44) reasoned about reality and the beliefs of characters in animated vignettes. In adults, a late slow wave (LSW), with a left-frontal scalp distribution, was associated with reasoning about beliefs. This LSW was also observed for children who could correctly reason about the characters' beliefs but not in children who failed false-belief questions. These findings have several implications, including support for the critical role of the prefrontal cortex for theory of mind development. [source]

The effect of stimulus intensity on brain responses evoked by transcranial magnetic stimulation

HUMAN BRAIN MAPPING, Issue 3 2004
Soile Komssi
Abstract To better understand the neuronal effects of transcranial magnetic stimulation (TMS), we studied how the TMS-evoked brain responses depend on stimulation intensity. We measured electroencephalographic (EEG) responses to motor-cortex TMS, estimated the intensity dependence of the overall brain response, and compared it to a theoretical model for the intensity dependence of the TMS-evoked neuronal activity. Left and right motor cortices of seven volunteers were stimulated at intensities of 60, 80, 100, and 120% of the motor threshold (MT). A figure-of-eight coil (diameter of each loop 4 cm) was used for focal stimulation. EEG was recorded with 60 scalp electrodes. The intensity of 60% of MT was sufficient to produce a distinct global mean field amplitude (GMFA) waveform in all subjects. The GMFA, reflecting the overall brain response, was composed of four peaks, appearing at 15 ± 5 msec (Peak I), 44 ± 10 msec (II), 102 ± 18 msec (III), and 185 ± 13 msec (IV). The peak amplitudes depended nonlinearly on intensity. This nonlinearity was most pronounced for Peaks I and II, whose amplitudes appeared to sample the initial part of the sigmoid-shaped curve modeling the strength of TMS-evoked neuronal activity. Although the response amplitude increased with stimulus intensity, scalp distributions of the potential were relatively similar for the four intensities. The results imply that TMS is able to evoke measurable brain activity at low stimulus intensities, probably significantly below 60% of MT. The shape of the response-stimulus intensity curve may be an indicator of the activation state of the brain. Hum. Brain Mapp. 21:154,164, 2004. © 2004 Wiley-Liss, Inc. [source]

The feedback correct-related positivity: Sensitivity of the event-related brain potential to unexpected positive feedback

PSYCHOPHYSIOLOGY, Issue 5 2008
Clay B. Holroyd
Abstract The N200 and the feedback error-related negativity (fERN) are two components of the event-related brain potential (ERP) that share similar scalp distributions, time courses, morphologies, and functional dependencies, which raises the question as to whether they are actually the same phenomenon. To investigate this issue, we recorded the ERP from participants engaged in two tasks that independently elicited the N200 and fERN. Our results indicate that they are, in fact, the same ERP component and further suggest that positive feedback elicits a positive-going deflection in the time range of the fERN. Taken together, these results indicate that negative feedback elicits a common N200 and that modulation of fERN amplitude results from the superposition on correct trials of a positive-going deflection that we term the feedback correct-related positivity. [source]