Download "Combined contributions of feedforward and feedback inputs to bottom-up attention"

In order to deal with a large amount of information carried by visual inputs entering
the brain at any given point in time, the brain swiftly uses the same inputs to
enhance processing in one part of visual field at the expense of the others. These
processes, collectively called bottom-up attentional selection, are assumed to solely rely
on feedforward processing of the external inputs, as it is implied by the nomenclature.
Nevertheless, evidence from recent experimental and modeling studies points to the role
of feedback in bottom-up attention. Here, we review behavioral and neural evidence that
feedback inputs are important for the formation of signals that could guide attentional
selection based on exogenous inputs. Moreover, we review results from a modeling study
elucidating mechanisms underlying the emergence of these signals in successive layers
of neural populations and how they depend on feedback from higher visual areas. We
use these results to interpret and discuss more recent findings that can further unravel
feedforward and feedback neural mechanisms underlying bottom-up attention. We argue
that while it is descriptively useful to separate feedforward and feedback processes
underlying bottom-up attention, these processes cannot be mechanistically separated into
two successive stages as they occur at almost the same time and affect neural activity
within the same brain areas using similar neural mechanisms. Therefore, understanding
the interaction and integration of feedforward and feedback inputs is crucial for better
understanding of bottom-up attention.