Abstract
Attentional modulation of Visual Evoked Potential (VEP) responses to black and white checkerboard patterns is readily observed, as reported in prior literature. However, results from more recent studies have shown that chromatic VEP responses, known to reflect largely early cortical processing, are robust to attentional modulation. Nonetheless, it is possible that the failure to observe attentional modulation for responses to chromatic stimuli in these studies may have resulted from saturation of the VEP response or insufficiently demanding attentional tasks. In the present study, we report full contrast response functions to chromatic and achromatic onset stimuli. In addition, we employed several levels of difficulty of a demanding distracting task, multiple object tracking (MOT), to ensure sufficient attentional modulation. The behavioral results reaffirm that the different levels of the MOT task are increasingly demanding. The VEP results support prior conclusions that chromatic onset VEP responses show little modulation with attentional shifts. We also replicated prior research that demonstrated strong attentional modulation of responses to standard achromatic (black and white) reversing checkerboard stimuli. However, surprisingly, we also failed to observe a modulation of responses to the achromatic onset grating stimuli, mirroring the results of the chromatic condition. Our findings demonstrate that 1) onset VEP responses to chromatic stimuli are insensitive to attentional shifts even for highly demanding tasks and 2) insensitivity holds over a large contrast range and 3) resistance to attentional modulation effects may not be restricted to the chromatic pathways. Further experiments are underway to clarify the discrepancy between the achromatic onset and reversal results.