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William X Ngiam, Edward Awh, Alex O Holcombe; Examining the effects of memory compression with the contralateral delay activity. Journal of Vision 2019;19(10):204a. doi: https://doi.org/10.1167/19.10.204a.
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While visual working memory (VWM) is limited in the amount of information that it can maintain, it has been found that observers can overcome the usual limit using associative learning. For example, Brady et al. (2009) found that observers showed improved recall of colors that were consistently paired together during the experiment. One interpretation of this finding is that statistical regularities enable subjects to store a larger number of individuated colors in VWM. Alternatively, it is also possible that performance in the VWM task was improved via the recruitment of LTM representations of well-learned color pairs. In the present work, we examine the impact of statistical regularities on contralateral delay activity (CDA) that past work has shown to index the number of individuated representations in VWM. Participants were given a bilateral color recall task with a set size of either two or four. Participants also completed blocks with a set size of four where they were informed that colors would be presented in pairs and shown which pairs would appear throughout, to encourage chunking of the pairs. We find this explicit encouragement of chunking improved memory recall but that the amplitude of the CDA was similar to the unpaired condition. Xie and Zhang (2017; 2018) previously found evidence that familiarity produces a faster rate of encoding as indexed by the CDA at an early time window, but no difference at a late time window. Using the same analyses on the present data, we instead find no differences in the early CDA, but differences in the late CDA. This result raises interesting questions about the interaction between the retrieval of LTM representations and what the CDA is indexing.
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