Subcortico-cortical pathways support ensemble-based outlier detection in humans

<title>Abstract</title> <p>Ensemble perception allows the visual system to summarize groups of objects without representing each item individually, but whether subcortical visual pathways contribute to this statistical computation remains unclear. Here, we combine psychophysics with 7-tesla functional MRI to demonstrate that extracting global orientation statistics engages a coordinated subcortico-cortical network. Behaviorally, task-irrelevant orientation outliers facilitated responses in proportion to their deviation from the implicit global ensemble mean, indicating that salience depends on global distributional structure rather than local physical contrast. In the scanner, participants reliably localized global outliers but not global-mean items. Global outliers selectively increased activity in early-to-intermediate visual cortex, the medial pulvinar, and the superior colliculus. Critically, the spatial location of outliers was specifically encoded in V4, V3B, medial pulvinar, and superior colliculus. Furthermore, generalized psychophysiological interaction analyses revealed that the detection of contralateral outliers was accompanied by enhanced functional coupling between subcortical nuclei and the visual cortex. These findings provide direct evidence for a subcortical contribution to human ensemble perception, highlighting a superior colliculus–pulvinar–cortical pathway specialized for the rapid statistical processing of visual scenes.</p>