Distinct working-memory organisation for the colour and duration of visual objects

When holding information 'in mind', it is essential that individual objects in working memory remain separated and accessible for guiding behaviour. Space is a well-established organising principle for retaining various features of visual objects in working memory, but whether this spatial organisation is universally applied across all features of visual objects remains unclear. Here, we tested whether two inherently non-spatial features of a visual item, colour and duration, rely on the same spatial organisation of working memory. To track this spatial organisation implicitly, we measured directional biases in microsaccades while participants were cued to select one of two memorised visual items in order to report either its colour or its duration, depending on the session. Crucially, while the visual stimuli were identical between the colour-report and the duration-report sessions, accessing colour information led to a robust spatial microsaccade bias towards the item's original location, whereas this bias was absent when accessing duration. This was corroborated by a significant difference in the spatial bias between the colour and duration sessions. We conclude that the memory organisation for colour and duration is distinct, even when memory regards the exact same visual objects. This implies that the spatial organisation of working memory for visual features is not universal, but feature-dependent.