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Abstract

Observers are often unaware of changes in their visual environment until attention is drawn to the location of change. Without focused attention, object representations are ephemeral and conscious detection of change does not occur. Focused attention appears to mediate change perception by giving objects coherence across space and time. To study the relation between focused attention and aware/unaware perception of change, we recorded Event Related Potentials (ERPs) from subjects performing a change blindness task. A complex scene was repeatedly presented for 500 ms, separated by a 300 ms blank mask. After several cycles, a change was introduced in the scene. Original and modified versions alternated for 40 flickers (unaware change, unattended location of change), or until the change was reported. A semantic cue was then displayed to help subjects identify the changing region. During the subsequent 30 to 40 flickers, subjects attended to that location and reported when the change was removed (aware change, attended location of change). Next, subjects looked for a second change in the same scene, usually absent (no change, unattended location of original change). Finally, subjects focused attention at the location of the original change to report its re-occurrence (no change, attended location of change). Preliminary analyses suggest different effects of focused attention, aware, and unaware perception of change.