Natural scene perception

Natural scene perception refers to the process by which an agent (such as a human being) visually takes in and interprets scenes that it typically encounters in natural modes of operation (e.g. busy streets, meadows, living rooms). This process has been modeled in several different ways that are guided by different concepts.

One major dividing line between theories that explain natural scene perception is the role of attention. Some theories maintain the need for focused attention, while others claim that focused attention is not involved.

Focused attention played a partial role in early models of natural scene perception. Such models involved two stages of visual processing. According to these models, the first stage is attention free and registers low level features such as brightness gradients, motion and orientation in a parallel manner. Meanwhile, the second stage requires focused attention. It registers high-level object descriptions, has limited capacity and operates serially. These models have been empirically informed by studies demonstrating change blindness, inattentional blindness and attentional blink. Such studies show that when one's visual focused attention is engaged by a task, significant changes in one's environment that are not directly pertinent to the task can escape awareness. It was generally thought that natural scene perception was similarly susceptible to change blindness, inattentional blindness and attentional blink, and that these psychological phenomena occurred because engaging in a task diverts attentional resources that would otherwise be used for natural scene perception.

The attention-free hypothesis soon emerged to challenge early models. The initial basis for the attention-free hypothesis was the finding that in visual search, basic visual features of objects immediately and automatically pop out to the person doing the visual search. Further experiments seemed to support this: Potter (as cited by Evans & Treisman, 2005) showed that high-order representations can be accessed rapidly from natural scenes presented at rates of up to 10 per second. Additionally, Thorpe, Fize & Marlot (as cited by Evans & Treisman) discovered that humans and primates can categorize natural images (i.e. of animals in everyday indoor and outdoor scenes) rapidly and accurately even after brief exposures. The basic idea in these studies is that exposure to each individual scene is too brief for attentional processes to occur, yet human beings are able to interpret and categorize these scenes.

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