The selection of behaviorally relevant information from cluttered visual scenes (often
referred to as "attention") is mediated by a cortical large-scale network consisting
of areas in occipital, temporal, parietal, and frontal cortex that is organized into
a functional hierarchy of feedforward and feedback pathways. In the human brain, little
is known about the temporal dynamics of attentional processing from studies at the
mesoscopic level of electrocorticography (ECoG), that combines millisecond temporal
resolution with precise anatomical localization of recording sites. We analyzed high-frequency
broadband responses (HFB) responses from 626 electrodes implanted in 8 epilepsy patients
who performed a spatial attention task. Electrode locations were reconstructed using
a probabilistic atlas of the human visual system. HFB responses showed high spatial
selectivity and tuning, constituting ECoG response fields (RFs), within and outside
the topographic visual system. In accordance with monkey physiology studies, both
RF widths and onset latencies increased systematically across the visual processing
hierarchy. We used the spatial specificity of HFB responses to quantitatively study
spatial attention effects and their temporal dynamics to probe a hierarchical top-down
model suggesting that feedback signals back propagate the visual processing hierarchy.
Consistent with such a model, the strengths of attentional modulation were found to
be greater and modulation latencies to be shorter in posterior parietal cortex, middle
temporal cortex and ventral extrastriate cortex compared with early visual cortex.
However, inconsistent with such a model, attention effects were weaker and more delayed
in anterior parietal and frontal cortex.