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Sisi Wang, Jason Rajsic, Geoffrey F. Woodman; The contralateral delay activity tracks the storage of sequentially presented colors and letters. Journal of Vision 2019;19(10):204c. doi: https://doi.org/10.1167/19.10.204c.
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The contralateral delay activity (CDA) is an event-related potential that is generally believed to be a neural index of visual working memory (VWM) storage, based on consistent electrophysiological findings that its amplitude during visual information retention period tracks the number of items stored in working memory. Despite the consistent and robust CDA findings for stimuli presented simultaneously in a visual array, there are still controversies about whether the amplitude of CDA reflects the storage of the summed number of sequentially presented stimuli, or attention to the most recently presented items. In the present experiment, event-related potentials were recorded while participants completed a lateralized visual change-detection task where each object was presented sequentially. Participants were shown bilateral pairs of one, three, or six sequentially presented colored squares or letters, such that they need to encode a single item in the attended hemifield with each stimulus onset. They then decided whether or not one of the objects in a test array were different from the stream of objects they had just seen. Behavioral accuracy of change detection decreased with increasing set size for colored squares and letters. The amplitude of CDA increased with the number of items stored in VWM for both colored squares and letters. These results suggest that the amplitude of CDA reflects the summed storage of sequentially presented stimuli and not only the most recently attended colored object or letter.
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