Mechanisms of directed attention in the human extrastriate cortex as revealed by functional MRI

Kastner, S., De Weerd, P., Desimone, R., & Ungerleider, L. G. (1998)

Science, 282(5386), 108-111.


A typical scene contains many different objects, but the capacity of the visual system to process multiple stimuli at a given time is limited. Thus, attentional mechanisms are required to select relevant objects from among the many objects competing for visual processing. Evidence from functional magnetic resonance imaging (MRI) in humans showed that when multiple stimuli are presented simultaneously in the visual field, their cortical representations within the object recognition pathway interact in a competitive, suppressive fashion. Directing attention to one of the stimuli counteracts the suppressive influence of nearby stimuli. This mechanism may serve to filter out irrelevant information in cluttered visual scenes.

Contribution to the field

This was the first paper testing the biased competition theory of attention with fMRI. We used a design in which the same stimuli were presented simultaneously or sequentially in the periphery during central fixation, with in the two conditions attention directed to one target location and stimulus, or not.  The main conclusions from GLM analysis later on were replicated by Kanwisher’s group (Reddy et al., PNAS, 2009) using MVPA: competing (simultaneously presented) stimuli will influence each other’s neural representation, while attended stimuli are protected from these competitive effects. These fMRI data are relevant because they suggest the operation of similar selective attention mechanisms in human extrastriate cortex as demonstrated before in Macaque neurophysiological recordings (e.g., Reynolds et al., J. Neurosci., 1999).

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