Electrophysiological correlates of high-level perception during spatial navigation

Abstract

We studied the electrophysiological basis of object recognition by recording scalp electroencephalograms while participants played a virtual-reality taxi driver game. Participants searched for passengers and stores during virtual navigation in simulated towns. We compared oscillatory brain activity in response to store views that were targets or nontargets (during store search) or neutral (during passenger search). Even though store category was solely defined by task context (rather than by sensory cues), frontal electrophysiological activity in the low frequency bands (primarily in the [4-8 Hz] band) reliably distinguished between the target, nontarget, and neutral store views. These results implicate low-frequency oscillatory brain activity in frontal regions as an important variable in the study of the cognitive processes involved in object recognition, categorization, and other forms of high-level perception.

Figure 1

The 128-channel Geodesic Sensor Net^™ used to measure the EEG and the regions of interest (ROI) on which the analyses were based. Each ROI is labeled with a 3 letter name that describes its position on the skull: R = right, L = left, S = superior, I = inferior, A = anterior, P = posterior

Figure 2

a. Top-down view of a possible town layout. Squares with s inside indicate store locations; dark squares surrounded by a lighter area indicate building and sidewalk locations. b. A passenger, store, and buildings within the virtual town. c. The store in this figure occupies approximately 0.35% of the display (arrow added for illustrative purposes).

Figure 3

Z-transformed power for neutral, non-target, and target store views. The labels on the abscissa show the mean time point of each bin (the first two time points in each panel, separated by a gray vertical line, show data from before the store presentation exceeded threshold). Because of the z-transformation, the means in each panel are constrained to start near 0 (because of different numbers of neutral, non-target, and target observations the central tendency of these means can deviate slightly from 0). The 5 columns show z-transformed power for the δ (2–4 Hz), θ (4–8 Hz), α (8–16 Hz), β (16–32 Hz), and γ (≥ 32 Hz) frequency bands. From top to bottom the panels show data from the left and right anterior inferior ({L,R}AI), anterior superior ({L,R}AS), posterior superior ({L,R}PS), and posterior inferior ({L,R}PI) regions of interest, respectively. Shaded gray areas show significant differences—except for the β frequency band, which shows a significant difference between neutral and non-target in the RAS region, light gray areas show significant differences between neutral and target store views, whereas dark gray areas denote significant differences between non-target and target store views.