Abstract
The capacity to integrate multiple sources of information is a prerequisite for complex cognitive ability, such as finding a target uniquely identifiable by the conjunction of two or more features. Recent studies identified greater frontal-parietal synchrony during conjunctive than non-conjunctive (feature) search. Whether this difference also reflects greater information integration, rather than just differences in cognitive strategy (e.g., top-down versus bottom-up control of attention), or task difficulty is uncertain. Here, we examine the first possibility by parametrically varying the number of integrated sources from one to three and measuring phase-locking values (PLV) of frontal-parietal EEG electrode signals, as indicators of synchrony. Linear regressions, under hierarchical false-discovery rate control, indicated significant positive slopes for number of sources on PLV in the 30–38 Hz, 175–250 ms post-stimulus frequency-time band for pairs in the sagittal plane (i.e., F3-P3, Fz-Pz, F4-P4), after equating conditions for behavioural performance (to exclude effects due to task difficulty). No such effects were observed for pairs in the transverse plane (i.e., F3-F4, C3-C4, P3-P4). These results provide support for the idea that anterior-posterior phase-locking in the lower gamma-band mediates integration of visual information. They also provide a potential window into cognitive development, seen as developing the capacity to integrate more sources of information.
Highlights
The capacity to integrate multiple sources of information is a prerequisite for complex cognitive behaviour
The slopes from linear regressions of arity onto phase-locking values (PLV) were computed from the mean PLVs for each frequency-time band and electrode pair combination, and their significances were corrected for multiple comparisons using the hierarchical false discovery rate method [20]
The false discovery rate (FDR) method first proposed in [28] is widely used for controlling false positives in neuroimaging, we found FDR to be too conservative for the analysis of PLV in EEG data
Summary
The capacity to integrate multiple sources of information is a prerequisite for complex cognitive behaviour. Subsequent work on humans using scalp electroencephalography (EEG) reported greater anteriorposterior synchrony for the conjunctive than feature condition in the same lower frequency band [15], using EEG phase-locking values (PLV) as measures of synchrony [16] These studies [14,15], were primarily designed to assess the differences in top-down and bottom-up control of attention–the single feature condition in these studies corresponds to the so-called popout condition (i.e., where all non-targets have the same features not shared with the target), which is generally faster and more efficient than when non-targets are distinct from each other (i.e., the distractor-distractor similarity effect) [17,18]. In light of our earlier result [15], we hypothesize a significant increase in synchrony (PLV) between frontal and parietal EEG electrodes as a function of the number of feature dimensions that uniquely identify the target in a 22–34 Hz frequency band around 160–480 ms into the search task (i.e., after the presentation of the search display)
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