Tracking an object through feature space

Visual attention allows an observer to select certain visual information for specialized processing. Selection is readily apparent in ‘tracking’ tasks where even with the eyes fixed, observers can track a target as it moves among identical distractor items1. In such a case, a target is distinguished by its spatial trajectory. Here we show that one can keep track of a stationary item solely on the basis of its changing appearance—specified by its trajectory along colour, orientation, and spatial frequency dimensions—even when a distractor shares the same spatial location. This ability to track through feature space bears directly on competing theories of attention, that is, on whether attention can select locations in space2,3,4, features such as colour or shape5,6,7, or particular visual objects composed of constellations of visual features. Our results affirm, consistent with a growing body of psychophysical8,9,10,11,12,13 and neurophysiological14,15,16 evidence, that attention can indeed select specific visual objects. Furthermore, feature-space tracking extends the definition of visual object17 to include not only items with well defined spatio-temporal trajectories18, but also those with well defined featuro-temporal trajectories.