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Open Access Publications from the University of California

Inter-item interference and systematic biases in visual memory

  • Author(s): Chunharas, Chaipat
  • Advisor(s): Serences, John T
  • Ramachandran, Vilayanur S
  • et al.
Abstract

Although our experience might convince us that our memory is limitless, researches showed that we could not precisely remember beyond 4-5 colors or orientations. One reason is that multiple items interfere and compete for limited resources. Interestingly, items not only interfere but also systematically “distort” each other in ways that make items more or less similar (i.e., attraction or repulsion biases). The main goal of the thesis is to investigate the complex relationships between multiple items in visual memory. We showed that inter-item interference could be reduced, hence memory performance is improved, by presenting stimuli further apart in 2D or 3D spatial position. Furthermore, we demonstrated inter-item systematic biases using a simple visual feature (color) as well as demonstrated the bias in more complex visual features (geometric shape and size). Lastly, we developed a general framework to explain when and why we sometime see attraction or repulsion biases. We propose that attraction and repulsion biases reflect different goals of memory system – to summarize or reduce confusion respectively. We showed that the repulsion bias was stronger when we make two memory items more confusable (colors were very similar, presentation time was very short, memory delay was longer). Importantly, the repulsion is stronger in subjects with better general performance (measuring from an independent portion of data) – suggesting an adaptive nature rather than lack of effort to produce precise responses. Using the same paradigm, we showed that the direction was switched to attraction bias when we promoted summarizing than discriminating by increasing the memory load (from 2 to 4 items). Due to our biological limitation, our brains could not and do not try to remember the “truth.” Rather, our memory is only a distorted truth, and that does not matter as long as it is still useful.

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