Evidence for a fixed capacity limit in attending multiple locations

Area of Science:

• Cognitive Psychology
• Neuroscience
• Human Attention Research

Background:

• Debate exists on whether human attention is flexibly allocated or discrete.
• Flexible resource models suggest attention can be divided variably.
• Discrete models propose a fixed limit on concurrently attended locations.

Purpose of the Study:

• To experimentally compare flexible-resource and discrete models of attention.
• To investigate the limits of concurrent spatial attention in humans.
• To determine if attentional limits are based on selection processes.

Main Methods:

• Participants were cued to attend a variable number of spatial locations.
• Orientation of a briefly presented target was reported.
• Cue-evoked neural activity was measured before target onset.

Main Results:

• Participant errors were best explained by a model with a fixed limit on attended locations.
• Flexible-resource models without a fixed limit poorly described the error data.
• Neural activity preceding target onset predicted these discrete performance limits.

Conclusions:

• Human visual attention is limited to a small, fixed number of discrete locations.
• These attentional limits are established by early selection processes.
• Findings support the discrete capacity hypothesis of human attention.