The information capacity of visual attention

This investigation begins with the conjecture that visual attention is subserved by a single, powerful, general-purpose processor with a fixed modest data capacity. We suggest that this limited capacity corresponds to a fixed amount of information, measured in bits. We measure how much information attention can handle by measuring how much we can restrict display information without affecting performance. The information capacity of a display is the product of the number of samples in the display and the number of bits required to represent each sample.

The attentive visual tasks we study are the detection of a stationary dot in a field of moving dots and the detection of a static square in a field of flashing squares. Performance of these tasks is reliable up to a critical number of elements k and then falls as k/n when the number of elements n increases beyond this critical number. Performance of both tasks was measured under two conditions: the single displacement (two-frame) and the continuous (many-frame) condition. The display information required for unimpaired performance in each of these tasks is low--across tasks and across observers. Observers in the single displacement versions of these tasks require only 30 to 60 bits of information; observers in the continuous tasks require an information rate of only 130 to 370 bits per second. These results support the conjecture that the attentive mechanism has a limited capacity.