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GiYeul Bae, Steven Luck; What Information Can Actually Be Decoded from the EEG in Visual Working Memory Tasks?. Journal of Vision 2017;17(10):339. doi: https://doi.org/10.1167/17.10.339.
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Previous research showed that a feature value stored in memory (WM) can be decoded via a spatial pattern of EEG oscillatory activity in the EEG alpha band (8-12 Hz). The present study sought to determine what information is actually being decoded. First, we asked whether orientation can be decoded when it is decoupled from location. In Experiment 1, observers performed an orientation delayed estimation task in which the orientation and the angular location of a sample stimulus were independently manipulated. We separately decoded both the orientation and the angular location. We found that pure orientation decoding was above chance, although it was considerably weaker than pure location decoding. Second, we investigated how precisely angular location information can be decoded. Decoding precision was computed by estimating the dispersion of the decoded response distributions, and we also compared decoding performance using different numbers of underlying channel tuning functions (CTFs). We found that the decoding precision reaches at asymptote at 8 CTFs, implying that the EEG can discriminate angular locations as small as 45 degrees of the angular space. Third, we found that the decoding was equally precise across different feature values and that it reflects both metric and categorical information. Fourth, we found that decoding is above chance when the decoding weights derived from one observer are applied to another observer, indicating some consistency in scalp topography. Fifth, by temporally separating data for training and testing, we found that the EEG codes both time-dependent and time-independent information. Lastly, using a 2AFC task, Experiment 2 showed that orientation decoding can be achieved using a task other than delayed estimation. Together, these findings provide several insights about what visual information is actively maintained in working memory and can be decoded from the EEG.
Meeting abstract presented at VSS 2017
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