The neural correlates of feature-based selective attention when viewing spatially and temporally overlapping images

Abstract

We used dense-array EEG to study the neural correlates of selective attention to specific features of objects that spatially overlapped an unattended image. Participants viewed superimposed images (horizontal and vertical bars differing in color) and attended to one image to identify bar width changes in specific locations. Images were frequency tagged so attention directed to unique parts of the stimuli could be tracked. Steady-state visual evoked potentials were used to quantify attention-related neural activity. As expected, selectively attending to specific parts of the attended image enhanced brain activity related to the attended element, and left unchanged activity elicited by spatially overlapping unattended stimuli. Under specific conditions, however, we found increased activity to unattended stimuli. The specificity of the selective attention effects presented herein, however, may be limited under certain complex stimulus conditions.

Figure 1

The two images (horizontal and vertical bars) used in these experiments are shown as spatially distinct, but they perfectly overlapped during testing. For the 7-bar study, both images were presented as they are shown here. For the 3-bar study, only the three middle bars of each image were presented to the participants (i.e. the middle bars and the peripheral bars). For the 5-bar study, only the five middle bars of each image were presented to the participants (i.e. the middle bars, the peripheral bars, and the outside bars that were immediately adjacent to the peripheral bars).

Figure 2

Head surface map of grand average FFT power to the steady-state stimuli (averaged over all frequencies and all conditions for all participants).

Figure 3

An example of power spectra averaged over the 67 EEG channels that captured the peak ssVEP power averaged over all participants for the 5-bar experiment. In this example, the green vertical middle bar, peripheral bars, and outside bars flickered at 7.69 Hz, 7.14 Hz, and 6.67 Hz, respectively. The red horizontal bars flickered at 8.33Hz. Participants attended to the green vertical bars, and were asked to identify width changes in the green middle and peripheral bars (A, the attend-all condition) or green middle bar only (B, the attend-mid condition).

Figure 4

Mean power (plus standard error) of the ssVEP for all three studies.

Figure 5

Bivariate scatter plot of change in middle bar d-prime values (narrow minus the broad attention conditions) as a function of the change in middle bar ssVEP power (narrow minus the broad attention conditions) in the 5-bar study.