Stimulus similarity modulates competitive interactions in human visual cortex

Beck, D. M., & Kastner, S. (2007). Stimulus similarity modulates competitive interactions in human visual cortex. Journal of Vision, 7(2), 19 11-12.

Abstract:
When multiple visual stimuli are simultaneously presented in a neuron's receptive field, they often interact with each other by mutually suppressing their visually evoked responses, suggesting that multiple stimuli present at the same time in the visual field compete for neural representation. Previous research has shown that these suppressive interactions can be biased by top-down influences such as spatially directed attention, as well as by the bottom-up factor of visual salience. Using fMRI, we asked whether competitive interactions might also be modulated by other bottom-up factors and tested the effects of stimulus similarity. Specifically, we found that suppressive interactions in area V4, measured by comparing activity evoked by simultaneous (potentially competing) and sequential (noncompeting) presentations, were reduced when four items were identical relative to when the four items differed in color and orientation. Such a result is consistent with the prediction that competition is more likely to occur between groups than within a group.

Note:
The stimulus similarity is related to the concept of perceptual grouping.

Because of the limitation of processing capacity, people have to suppress the irrelevant information. Biased competition theory has been proposed to explain how people select and inhibit the information. Top-down and bottom process both influence the selection of information. This hypothesis may predict that suppressive interactions only occur between rather than within perceptual groups. There is no need to inhibit the irrelevant information when stimuli were grouped. Previous findings also showed that the activity in the intermediate visual area was less active when stimuli were simultaneously presented than when stimuli were sequentially presented, because simultaneous presentation leads to compete with the limited capacity.
To combine the grouping and temporal properties in stimuli presentation, the authors manipulated four gabor patches in color and orientation with simultaneous or sequential presentation. Participants were required to identify the target letter in the center while the gabor patches were presented in the receptive field. Results showed an interaction between the stimulus type (grouping) and type of presentation. When stimuli were grouped, there was no difference between different types of presentation. In contrast, when stimuli were not grouped, it shoed visual area is less active with a simultaneous presentation than with a sequential presentation.

I think this result can be applied to what I have done about the attention selection on features of an attended object. Because features were grouped based on the same location, no competition should be observed (biased competition occurs among different stimuli). The effect of feature-based selection on visual memory should be discussed.