The Role of Object Recognition in Scene Segmentation

M.J. Bravo and H. Farid

Investigative Opthalmology and Visual Science (ARVO), Fort Lauderdale, FL, 2000

Purpose. How does our familiarity with the objects in our environment affect the way we organize the visual world? To find out, we tested how well subjects could segment 3D scenes with ambiguous low-level grouping cues.

Methods. 3D block objects were generated by a simple computer algorithm which neatly stacked 6-8 colored blocks next to or on top of one another. Subjects were trained to recognize four of these block objects. Block scenes were then created by aligning several block objects next to each other such that the object boundaries were completely ambiguous. These block scenes were either composed of the familiar (learned) or unfamiliar objects. Placed neatly in the scene was a target object consisting of four blocks. A new target was used on each trial, and subjects were either shown the target before they were shown the scene (precue) or after they were shown the scene (postcue). The subject's task was to determine whether the target was present in the scene.

Results. In the precue condition, there was no effect of familiarity on accuracy: subjects could search a scene of unfamiliar objects as effectively as a scene of familiar objects. In contrast, the postcue condition showed a large effect of familiarity on accuracy: subjects rarely reported the presence of the target in scenes composed of unfamiliar objects, but they performed quite well with scenes of familiar objects. With scenes of familiar objects, subjects reported that they first identified the block objects and then directed their attention to ``what was left over''.

Conclusions. Subjects appear to be able to organize a scene into familiar objects in the absence of low-level grouping cues. It is this organization that allows them to find a target before they know what it looks like (postcue). If subjects do know what the target looks like (precue), then this perceptual organization appears to play no role in search.