Simultaneous Recording Reveals Attentional Modulation of Chromatic Visual Evoked Potentials

Abstract

Prior research has shown that the chromatic pattern-onset VEP is robust to attentional manipulations when test and distracter stimuli are either superimposed or spatially separated. These results suggest that the chromatic VEP response is occurring early (V1) and may not be sensitive to feedback from attentional mechanisms. We report here studies of chromatic and achromatic VEP responses recorded in the presence of attentional modulation using stimulus parameters designed to reduce variability and favor detection of small attentional effects. VEPs were recorded to attended and unattended stimuli simultaneously in separate hemifields using a frequency-tagged averaging technique and task relevant distracters. Additionally, stimuli were perceptually equated and presented close to the fovea. Under these conditions, small but significant attentional modulations of the chromatic waveform amplitudes are revealed. In addition, we explore effects of attentional modulation across both chromatic LM and S, and the achromatic visual pathways. These results showed adaptation effects that were independent of distracter pathway. A Further exploration is required however, since the results from a control experiment to rule out a fixation bias towards the attended stimuli failed to eliminate shifts in fixation as the cause for the observed attentional effects.