Publications

AuthorTitleTypeYear
Applied Filters: First Letter Of Last Name: N Reset
3 Publications

N

Noll, D., Genovese, C., Nystrom, L. E., Vazquez, A. L., Forman, S. D., Eddy, W., & Cohen, J. D. (1997). Estimating test‐retest reliability in functional MR imaging II: Application to motor and cognitive activation studies. Magnetic Resonance in Medicine, 38, 508–517. https://doi.org/10.1002/mrm.1910380320
Functional magnetic resonance imaging (fMRI) using blood oxygenation contrast has rapidly spread into many application areas. In this paper, a new statistical model is used to evaluate the reliability of fMRI activation in a finger opposition motor paradigm for both within‐session and between‐session data and in a working memory paradigm for between‐session data. A slice prescription procedure for between‐session reproducibility is introduced. Estimates are made for the probabilities of correctly and falsely classifying voxels as active or inactive and receiver operator characteristic curves are generated. In the motor paradigm, estimated between‐session reliability was found to be somewhat reduced relative to within‐session reliability; however, this includes additional sources of variation and may not reflect intrinsically lower reliability. After matching false‐positive classification probabilities, between‐session reliability was found to be nearly identical for both motor and cognitive activation paradigms.
Nystrom, L. E., & McClelland, J. L. (1992). Trace synthesis in cued recall. Journal of Memory and Language, 31, 591–614. https://doi.org/10.1016/0749-596x(92)90030-2

Several memory models propose that recall may combine traces of different memories. Such models predict blend errors during cued recall. To examine memory blending during recall, four experiments were performed. In each experiment, subjects rated the plausibility of several sentences, many of which shared words with one other sentence. Later, they were asked to recall words from a single sentence to complete partial-sentence cues. When the cue matched two study sentences, subjects made blend errors, recalling one word from each study sentence more frequently than in a control condition. Blend errors were relatively infrequent, however, occurring on about 5% of opportunities. A good account of the results was provided by a stochastic interactive activation model that causes blend errors by synthesizing traces during retrieval.

Nystrom, L. E., Braver, T. S., Sabb, F. W., Delgado, M. R., Noll, D., & Cohen, J. D. (2000). Working Memory for Letters, Shapes, and Locations: fMRI Evidence against Stimulus-Based Regional Organization in Human Prefrontal Cortex. NeuroImage, 11, 424–446. https://doi.org/10.1006/nimg.2000.0572
Investigations of working memory (WM) systems in the frontal cortex have revealed two stimulus dimensions along which frontal cortical representations may be functionally organized. One hypothesized dimension dissociates verbal from nonverbal WM processes, dividing left from right frontal regions. The second hypothesized dimension dissociates spatial from nonspatial WM, dividing dorsal from ventral frontal regions. Here we used functional magnetic resonance imaging to probe WM processes associated with three different types of stimuli: letters (verbal and nonspatial), abstract shapes (nonverbal and nonspatial), and locations (nonverbal and spatial). In a series of three experiments using the “n-back” WM paradigm, direct statistical comparisons were made between activation patterns in each pairwise combination of the three stimulus types. Across the experiments, no regions that demonstrated responses to WM manipulations were discovered to be unique to any of the three stimulus types. Therefore, no evidence was found to support either a left/right verbal/nonverbal dissociation or a dorsal/ventral spatial/nonspatial dissociation. While this could reflect a limitation of the present behavioral and imaging techniques, other factors that could account for the data are considered, including subjects strategy selection, encoding of information into WM, and the nature of representational schemes in prefrontal cortex.

Related links