Frontolimbic response to negative feedback in clinical depression

Functional neuroimaging suggests that limbic regions of the medial frontal cortex may be abnormally active in individuals with depression. These regions, including the anterior cingulate cortex, are engaged in both action regulation, such as monitoring errors and conflict, and affect regulation, such as responding to pain. The authors examined whether clinically depressed subjects would show abnormal sensitivity of frontolimbic networks as they evaluated negative feedback. Depressed subjects and matched control subjects performed a video game in the laboratory as a 256-channel EEG was recorded. Speed of performance on each trial was graded with a feedback signal of A, C, or F. By 350 ms after the feedback signal, depressed subjects showed a larger medial frontal negativity for all feedback compared with control subjects with a particularly striking response to the F grade. This response was strongest for moderately depressed subjects and was attenuated for subjects who were more severely depressed. Localization analyses suggested that negative feedback engaged sources in the anterior cingulate and insular cortices. These results suggest that moderate depression may sensitize limbic networks to respond strongly to aversive events.     

Measuring incremental changes in word knowledge: Experimental validation and implications for learning and assessment

The goal of this study was to test a new technique for assessing vocabulary development. This technique is based on an algorithm for scoring the accuracy of word definitions using a continuous scale (Collins-Thompson & Callan, 2007). In an experiment with adult learners, target words were presented in six different sentence contexts, and the number of informative versus misleading contexts was systematically manipulated. Participants generated a target definition after each sentence, and the definition-scoring algorithm was used to assess the degree of accuracy on each trial. We observed incremental improvements in definition accuracy across trials. Moreover, learning curves were sensitive to the proportion of misleading contexts, the use of spaced versus massed practice, and individual differences, demonstrating the utility of this procedure for capturing specific experimental effects on the trajectory of word learning. We discuss the implications of these results for measurement of meaning, vocabulary assessment, and instructional design.     

Differentiating the N3 and N4 electrophysiological semantic incongruity effects

An event-related potential termed the N4 has been widely studied due to its sensitivity to semantic incongruity. A recent report (Nobre & McCarthy, 1994) indicates there is also an N3 component that is sensitive to semantic incongruity. To differentiate these two components, an existing data set with 65 electrode sites, 78 subjects, and 120 sentences was examined. Instead of the usual procedure of averaging over the stimuli within distinct categories for each subject, a new approach--averaging over subjects--was employed. In this item average approach, 120 averages (one per sentence) were produced. Correlational analyses indicate that the N3 is equally sensitive to cloze probability and sentential constraint. The N4, by contrast, is more sensitive to sentential constraint and less to cloze probability; it is also correlated with familiarity. We interpret these results as evidence that the N3 is more responsive to semantic fit whereas the N4 is more responsive to semantic expectancy.     

Hemispheric differences in strong versus weak semantic priming: evidence from event-related brain potentials

GOALS: Research with lateralized word presentation has suggested that strong ("close") and weak ("remote") semantic associates are processed differently in the left and right cerebral hemispheres [e.g., Beeman, M. j., & Chiarello, C. (1998). Complementary right- and left-hemisphere language comprehension. Current Directions in Psychological Science, 7(1), 2-8]. Recently, this hypothesis has been challenged [Coney, J. (2002). The effect of associative strength on priming in the cerebral hemispheres. Brain and Cognition, 50(2), 234-241]. We predicted that foveal presentation of strong and weak associates would elicit different patterns of hemispheric activity, as indexed by high-density event-related brain potentials (ERPs), and that source localization of the scalp potentials would help clarify the nature of hemispheric contributions to semantic organization. METHODS: 128-channel ERPs were recorded in two experiments as subjects performed a lexical decision task. Word trials were equally divided into strongly related, weakly related, and unrelated word pairs. All words were foveally presented. SOA was 800 ms in Experiment 1, and 200 ms in Experiment 2. RESULTS: Topographic analyses revealed medial frontal (MFN) and parietal (N400/LPC) effects for both strong and weak associates. Between approximately 450 and 550 ms, the magnitude of the N400/LPC effect indicated priming for both strong and weak associates over left parietal sites, while priming over right parietal sites was restricted to strongly related word pairs. During this interval, spatiotemporal source modeling showed that these scalp effects were best accounted for by ipsilateral sources in the medial temporal lobe. The observed pattern of asymmetries for strong versus weak associates is not consistent with certain proposals regarding the complementarity of right- and left-hemisphere contributions to semantics. It is, however, consistent with findings from visual half-field studies (Hasbrooke and Chiarello, 1998). We discuss the relevance of these results for theories of hemispheric asymmetry and meta-control in lexical semantic access.