Abstract
The visual system can efficiently summarize information by extracting ensemble statistics suchas the average of visual features. However, it remains unclear how ensemble perceptionoperates when individual features are grouped into meaningful objects. In the present study,we investigated whether ensemble statistics of local features can still be extracted whenoriented line segments form letters. Across two experiments, observers estimated the averageorientation of line elements either as unconnected lines in a typical ensemble display, arrangedinto intact letters, or transformed into pseudo-letters. Although the number and orientation ofline elements were identical across conditions, grouping into meaningful letters systematicallyimpaired performance. Grouping interfered with observers’ ability to estimate averageorientation when intact letters did not provide a useful global orientation cue, leading to largererrors and greater response variability than pseudo-letters or ungrouped lines. However, whenthe average orientation coincided with the mirror-symmetry axis of a letter, observers couldrely on this global structure, resulting in improved performance. Crucially, these effectsreplicated in peripheral vision, indicating that ensemble extraction is constrained by perceptualorganization even when access to local feature information is limited. Together, these resultsshow that ensemble perception is modulated by object-based grouping and perceptualorganization.