New technique will enhance understanding of little-understood vision phenomenon

Jun 1 2005

Look at something red in the room, and you'll be more likely to notice something red out of the corner of your eye, elsewhere in the room. Researchers have known that this "implicit attentional selection" is outside conscious control and that we are unaware of its functioning.

Researchers, led by David Melcher of Oxford Brookes University and Zoltán Vidnyánszky of the Hungarian Academy of Sciences and Semmelweis University, have developed an experimental technique for measuring the processing of visual input outside the focus of attention as a function of what subjects are concentrating on inside their attentional focus. Their technique will enhance study of this little-understood phenomenon, they said. The research is published in the June 2 issue of Neuron.

For example, they used their technique to show that, in the process of implicit attentional selection, different features of an object are automatically "clustered." For example, subjects asked to pay attention to a particular color also attend to the motion of objects of the same color throughout the visual field.

The researchers' technique consisted basically of asking subjects to pay attention to either of two separate populations of moving colored dots on a computer display. Asking the subjects to switch their attention from one set of dots to the other, the researchers manipulated the color and motion of the dots such that they could test how well the subjects discriminated one feature, say movement, while paying attention to another.

They were even able to manipulate the experiment so that subjects would misperceive that the color and motion were "misbound." In such circumstances, the subjects still linked features, indicating that such linkage reflected perception of actual relationships between the features and could not be "fooled."

The researchers also sought to understand the difference between the "binding" of features that are within the focus of attention from those outside that focus.

"Our findings also imply that feature binding inside the focus of attention is object based and links all features belonging to the same surface or object, whereas binding outside the attentional focus is based on the physical spatiotemporal relationship between the features," they wrote.

They concluded that the perceptual system thus uses two different methods of binding features--an automatic binding that occurs throughout the visual field and another mechanism that is under attentional control.

"Our new approach for examining cross-feature attention effects may provide an effective tool in further studies to characterize the different stages and mechanism of feature binding both inside and outside the locus of attention," concluded Melcher and his colleagues.