If humans see two objects in quick succession (less than 700 ms), they are only able to focus on one of them. This phenomenon is a specific type of the more general “information processing bottleneck” found in many cognitive systems.
Prior research has suggested that this deficiency in human processing is due to “later” mechanisms such as working memory and spatial selection. Williams et al. suggest in their 2008 paper that the problem may arise from earlier systems such as the primary visual cortex. In order to do so they used a novel spatial orientation, displaying the first object at the fovea and the second object in the periphery of the visual field.
Using fMRI, the researchers found a statistically significant correlation between BOLD activity in the primary visual cortex and the attentional blink activity (which they also found evidence for, but that is unsurprising).
They also found some intriguing data about an effect known as “lag-1 sparing,” which is that there was less attentional blink deficiency shown when the first and second object were shown at the same time than when they were separated by 200 ms. The common explanation for this effect was that subjects can view both of the objects at once because they are in the same spatial location, but these results show that the objects need not be in the same location (recall that object one is in the fovea but object two is in the periphery of the visual field). One possible way to explain this data is that subjects could divide their attention between the objects, enabling them both to be in the same “attentional gate.” This is a testable hypothesis–if attention is divided, evidence of details in either object would perhaps be less lucid.
Their results throw a curveball into the literature, as the effect must now be considered as a feedback result from upstream processing instead of purely an attentional deficiency. An interesting paper with some avenues for further research.
Williams MA, Visser TA, Cunnington R, Mattingley JB. 2008 Attenuation of neural responses in primary visual cortex during the attentional blink. Journal of Neuroscience 28:9890-9840. doi:10.1523/JNEUROSCI.3057-08.