A new method for off-line removal of ocular artifact.
ABSTRACT A new off-line procedure for dealing with ocular artifacts in ERP recording is described. The procedure (EMCP) uses EOG and EEG records for individual trials in an experimental session to estimate a propagation factor which describes the relationship between the EOG and EEG traces. The propagation factor is computed after stimulus-linked variability in both traces has been removed. Different propagation factors are computed for blinks and eye movements. Tests are presented which demonstrate the validity and reliability of the procedure. ERPs derived from trials corrected by EMCP are more similar to a 'true' ERP than are ERPs derived from either uncorrected or randomly corrected trials. The procedure also reduces the difference between ERPs which are based on trials with different degrees of EOG variance. Furthermore, variability at each time point, across trials, is reduced following correction. The propagation factor decreases from frontal to parietal electrodes, and is larger for saccades than blinks. It is more consistent within experimental sessions than between sessions. The major advantage of the procedure is that it permits retention of all trials in an ERP experiment, irrespective of ocular artifact. Thus, studies of populations characterized by a high degree of artifact, and those requiring eye movements as part of the experimental task, are made possible. Furthermore, there is no need to require subjects to restrict eye movement activity. In comparison to procedures suggested by others, EMCP also has the advantage that separate correction factors are computed for blinks and movements and that these factors are based on data from the experimental session itself rather than from a separate calibration session.
SourceAvailable from: Mikael Heimann[Show abstract] [Hide abstract]
ABSTRACT: The present study combines behavioral observations of memory (deferred imitation, DI, after a brief delay of 30 min and after a long delay of 2-3 weeks) and electrophysiological (event-related potentials, ERPs) measures of associative memory, as well as parental reports of non-verbal and verbal communication in sixteen 14-months-old children. Results show that for DI, the children remembered the stimulus after the brief but not after the long delay. There was a clear electrophysiological response indicating associative memory. Furthermore, a correlation between DI and ERP suggests that both measures of memory (DI and associative memory) tap into similar mechanisms in 14-months-old children. There was also a statistically significant relation between parental report of receptive (verbal) language and the ERP, showing an association between receptive language skills and associative memory.Frontiers in Psychology 01/2015; 6:260. DOI:10.3389/fpsyg.2015.00260 · 2.80 Impact Factor
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ABSTRACT: Affective stimuli such as emotional words, scenes or facial expressions elicit well-investigated emotional responses. For instance, two distinct event-related brain potentials (ERPs) have been reported in response to emotional facial expressions, the early posterior negativity (EPN), associated with enhanced attention and perception of affective stimuli, and a later centro-parietal positivity (LPP) that is taken to reflect evaluations of the intrinsic relevance of emotional stimuli. However, other rich sources of emotions that have as yet received little attention are internal mental events such as thoughts, memories and imagination. Here we investigated mental imagery of emotional facial expressions and its time course using ERPs. Participants viewed neutral familiar and unfamiliar faces, and were subsequently asked to imagine the faces with an emotional or neutral expression. Imagery was compared to visually perceiving the same faces with the different expressions. Early ERP modulations during imagery resemble the effects frequently reported for perceived emotional facial expressions, suggesting that common early processes are associated with emotion perception and imagination. A later posterior positivity was also found in the imagery condition, but with a different distribution than for perception. These findings underscore the similarity of the brain's responses to internally generated and external sources of emotions.NeuroImage 01/2015; · 6.13 Impact Factor
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ABSTRACT: The present study examined whether processing words with affective connotations in a listener's native language may be modulated by accented speech. To address this question, we used the Event Related Potential (ERP) technique and recorded the cerebral activity of Spanish native listeners, who performed a semantic categorization task, while listening to positive, negative and neutral words produced in standard Spanish or in four foreign accents. The behavioral results yielded longer latencies for emotional than for neutral words in both native and foreign-accented speech, with no difference between positive and negative words. The electrophysiological results replicated previous findings from the emotional language literature, with the amplitude of the Late Positive Complex (LPC), associated with emotional language processing, being larger (more positive) for emotional than for neutral words at posterior scalp sites. Interestingly, foreign-accented speech was found to interfere with the processing of positive valence and go along with a negativity bias, possibly suggesting heightened attention to negative words. The manipulation employed in the present study provides an interesting perspective on the effects of accented speech on processing affective-laden information. It shows that higher order semantic processes that involve emotion-related aspects are sensitive to a speaker's accent.Frontiers in Psychology 01/2015; 6:351. DOI:10.3389/fpsyg.2015.00351 · 2.80 Impact Factor