Attending to depth: electrophysiological evidence for a viewer-centered asymmetry

It has been proposed that the configuration of visuospatial attention in depth is viewer-centered such that an attentional gradient is concentrated between an observer and attended depth, trailing off steeply beyond. To investigate this asymmetry, event-related potentials were recorded while participants attended to far or near depths in a pictorial scene. The attention-sensitive visual components, PI (100-160 ms) and NI (160-220 ms), were assessed for amplitude differences. Amplitude enhancement of the PI component was present when participants attended far but not near depths. Reaction time facilitation also followed this pattern. Results are consistent with a viewer-centered asymmetry because such a configuration predicts the gradient of attention to distribute differentially to far depths but to remain constant for near depths.