Advances in multifocal methods for imaging human brain activity

Thom Carney*, Justin Ales, Stanley A. Klein

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution

8 Citations (Scopus)


The typical multifocal stimulus used in visual evoked potential (VEP) studies consists of about 60 checkerboard stimulus patches each independently contrast reversed according to an m-sequence. Cross correlation of the response (EEG, MEG, ERG, or fMRI) with the m-sequence results in a series of response kernels for each response channel and each stimulus patch. In the past the number and complexity of stimulus patches has been constrained by graphics hardware, namely the use of look-up-table (LUT) animation methods. To avoid such limitations we replaced the LUTs with true color graphic sprites to present arbitrary spatial patterns. To demonstrate the utility of the method we have recorded simultaneously from 192 cortically scaled stimulus patches each of which activate about 12mm 2 of cortex in area V1. Because of the sparseness of cortical folding, very small stimulus patches and robust estimation of dipole source orientation, the method opens a new window on precise spatio-temporal mapping of early visual areas. The use of sprites also enables multiplexing stimuli such that at each patch location multiple stimuli can be presented We have presented patterns with different orientations (or spatial frequencies) at the same patch locations but independently temporally modulated, effectively doubling the number of stimulus patches, to explore cell population interactions at the same cortical locus. We have also measured nonlinear responses to adjacent pairs of patches, thereby getting an edge response that doubles the spatial sampling density to about 1.8 mm on cortex.

Original languageEnglish
Title of host publicationHuman Vision and Electronic Imaging XI - Proceedings of SPIE-IS and T Electronic Imaging
Publication statusPublished - 2006
EventHuman Vision and Electronic Imaging XI - San Jose, CA, United States
Duration: 16 Jan 200618 Jan 2006

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


ConferenceHuman Vision and Electronic Imaging XI
Country/TerritoryUnited States
CitySan Jose, CA


  • Brain imaging
  • m-sequence
  • Multi-pattern
  • Multifocal
  • Sprite
  • VEP
  • Visual cortex


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