Covert Paradigm Research Articles

Effects of Covert and Overt Paradigms in Clinical Language fMRI

The aim of this study was to assess the intrasubject and intersubject reproducibility of functional magnetic resonance imaging (fMRI) language paradigms on language localization and lateralization. Fourteen healthy volunteers were enrolled prospectively and underwent language fMRI using visually triggered covert and overt sentence generation (SG) and word generation (WG) paradigms. Semiautomated analysis of all functional data was performed using Brain Voyager on an individual basis. Regions of interest for Broca's area, Wernicke's area, and their contralateral homologues were drawn. The Euclidean coordinates of the center of gravidity (x, y, and z) of the respective blood oxygenation level-dependent (BOLD) activation cluster, and the correlation of the measured hemodynamic response to the applied reference function (r), relative BOLD signal change as BOLD signal characteristics were measured in each region of interest. Regional lateralization indexes were calculated for Broca's area, Wernicke's area, and their contralateral homologues separately. Wilcoxon's signed-rank test was applied for statistical comparisons (P values < .05 were considered significant). Ten of the 14 volunteers had three repeated measurements to test intrasession reproducibility and intersession reproducibility. Overall activation rates for the four paradigms were 89% for covert SG, 82% for overt SG, 89% for covert WG, and 100% for overt WG. When comparing covert and overt paradigms, language localization was significantly different in 17% (Euclidean coordinates) and 19% (BOLD signal characteristics), respectively. Language lateralization was significantly different in 75%. Intrasubject and intersubject reproducibility was excellent, with 3.3% significant differences among all five parameters for language localization and 0% significant differences for language lateralization using covert paradigms. Covert language paradigms (SG and WG) provided highly robust and reproducible localization and lateralization of essential language centers for scans performed on the same and different days. Their overt counterparts achieved confirmatory localization but lower lateralization capabilities. Reference data for presurgical application are provided.

The effect of knowledge of correct results per item on verbal learning and retention

A report of an experiment to measure the effects of both overt and covert responses to educational stimuli with KCR (knowledge of correct results) feedback provided. In most studies of feedback, KCR (or KR) is given as a consequence of an overt response: Stimulus-Response-Feedback. In the case of a covert response, the student constructs his answer but does not react “overtly” to the presentation of a stimulus item. Forty Ss were randomly assigned to 1 of 4 groups further divided into 1 control group receiving no feedback and 3 groups receiving information (KCR) according to either overt or covert response patterns. A 25-item multiple-choice test was administered 5 times by means of a terminal consisting of a screen and a teletype. Results showed that the covert paradigm was the most effective. The experiment did not demonstrate that the covert process leads to better performance on a test administered later to measure retention. A tentative explanation for this negative result was that the time interval between the provision of feedback and presentation of the next item was of some relevance. A multiple comparison test revealed that the 3 treatment groups performed better than the control group.