Neural Correlates of Learning During a Visual Search Task

Abstract

Performance on visual search tasks can be improved with training; however, the neural mechanisms underlying such improvement are not clear. For example, although response times (RTs) typically shorten with training, it is unclear which components of the stimulus-response processing chain are facilitated and lead to the faster behavioral output. In principle, enhanced search abilities could result from improvements in various distinct cognitive stages along the stimulus-response processing chain, including: (1) faster attentional shifts to the target, (2) faster or better discrimination of the target, (3) faster motor-response preparation, and (4) faster response execution. To explore the loci of cognitive and neural plasticity resulting from visual-search training, we measured EEG as individuals performed a multi-day visual-search training protocol. Over the course of five days, we assessed changes in RTs and in various stimulus-processing-related ERP components: the N2pc (attentional shifting to target), the SPCN (manipulation and/or retention of information in visual short-term memory relevant for target discrimination processes), and the LRP (preparation for motor response). Participants were presented with circular arrays of colored ellipses and reported the orientation of a color-popout target as quickly and accurately as possible. Across the training period, RTs decreased by ~70ms. ERP analyses indicated that neither the amplitude nor latency of the N2pc component changed, suggesting that the training-related RT improvement did not derive from accelerated attentional shifting. In contrast, the onset latency of the LRP shifted earlier, suggesting improvement on the processing between the attentional shift and the motor-response initiation. Relatedly, the SPCN decreased substantially in amplitude with training, consistent with a facilitated target-discrimination process. Lastly the time between the LRP onset and the RT decreased, suggesting additional training effects on motor-execution speed. The present results thus help delineate several key phases of the stimulus-response processing chain that underlie visual-search RT improvement with training.