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The Time It Takes to Comprehend What You See

When you view an object, information about its color, shape and motion travels to the brain through separate neurons. This segregation of visual information raises the question: how do these signals become integrated to give rise to coherent perception? John Reynolds, associate professor in the Systems Neurobiology Laboratory, and Clara Bodelón, a mathematician in the laboratory, have taken a step toward understanding the mechanisms of perceptual integration by precisely timing them. They report in the Journal of Neuroscience that an object's properties are re-integrated in the cortex in 1/100th of a second.

To make that measurement, Bodelón designed pairs of simple images – for example a red vertical grating pattern and a green horizontal grating, or a rightward yellow grating and a leftward blue grating – which, when repeatedly presented very rapidly to human observers, cancelled one another and become invisible.

Bodelón found that when she slowed the presentation, the subjects could report the orientations of the gratings. When presentation rate was further lowered, the subjects perceived the colors and orientations but couldn't say which image – the vertical or horizontal one – was red or green. Their brains could "see" form and color but could not combine them.

Only after slowing the presentation by another 1/100th of a second could observers perceive the conjunctions of color and orientation of individual objects, indicating that the underlying computation is very fast, but measurably time-consuming.

Knowing the time required to integrate different sources of visual input has implications for ultimately treating disorders of perception, such as visual agnosia, a condition in which the patient has difficulty understanding complex visual stimuli.