Multivoxel Coding of Visual Stimuli is Flexible: Frontoparietal and Visual Cortices Adapt to Code the Currently Relevant Distinction

• ¹ Perception in Action Research Centre (PARC), Department of Cognitive Science, Faculty of Human Sciences, MQ, Australia
• ² ARC Centre of Excellence in Cognition and its Disorders, Cognitive Science, MQ, Australia
• ³ Perception in Action Research Centre (PARC), Department of Cognitive Science, Faculty of Human Sciences, MQ, Australia

Human cognition is characterised by astounding flexibility, which enables us to select which cognitive process to engage to best succeed in our current objective. However, we have, at present, an incomplete understanding of how such flexibility could be implemented in the brain. There is a well-defined circuit of frontal and parietal areas, referred to as multiple-demand (MD) regions, that are believed to play a fundamental role. The proposal is that MD regions dynamically adjust their responses in order to selectively process information that is currently relevant for behaviour ("adaptive coding hypothesis", Duncan 2001). We tested this hypothesis using multivariate pattern analysis (MVPA) of functional magnetic resonance imaging (fMRI) data while subjects performed a perceptually challenging discrimination task on novel abstract objects. Subjects were trained to classify objects along two orthogonal dimensions, dependent on current task context (length or orientation, indicated by a cue). In the scanner subjects performed short (2 minute) alternating blocks of the length and orientation tasks. We predicted that multi-voxel patterns of activation in the MD regions would adjust to code the stimulus distinction that was currently relevant for the task (i.e. to code for stimulus length, but not orientation, when length was relevant, and vice versa). In line with our prediction only the task-relevant stimulus distinctions (length in length task, and orientation in orientation task), and not the task-irrelevant ones, were coded in the MD regions. Interestingly, object-selective cortex in the lateral occipital complex (LOC) also adjusted to code relevant but not irrelevant stimulus distinctions, underscoring this region's role in demanding visual tasks. In line with the adaptive coding hypothesis, the data suggest a flexible neural system that adjusts its representation of visual objects to encode only the stimulus distinctions that are currently relevant for behaviour.