Abstract
What are the neuronal correlates of enhanced target stimulus saliency among distractors acquired while learning visual search tasks? We have addressed this question in three different experiments, each time using demanding visual search tasks that employ feature conjunction stimuli. In each experiment participants performed several training sessions. Brain activity, as measured by functional MRI scanning, was compared before and after training. In Experiment 1 participants learned to detect a red-green bisected disk among green-red bisected disk distractors by performing covert search (Frank et al., Hum Brain Mapp, 2014, 35, 1201-1211). In Experiment 2 we used the same red-green stimuli and, in addition, differently oriented T and L stimuli whereby a L-target had to be detected among T-distractors. As in Experiment 1 participants completed training sessions using covert search but, in contrast to Experiment 1, performed an attentionally demanding orthogonal task at fixation during scanning. In Experiment 3 participants viewed a radial array of moving dots and learned to detect a target dot with a “V”-shaped motion trajectory among distractors with an inverted “V”-shaped motion trajectory, again using covert search. In each of these experiments we found that the BOLD response in correct trials to the target at the respective retinotopic projection zone in visual cortex was enhanced relative to responses to the simultaneously presented distractors. Compared to pre-training, this effect was more pronounced after training and observed during covert search for the target (Experiments 1 and 3). This target-specific enhancement also persisted when attention was distracted by the fixation task (Experiment 2). We conclude that a retinotopic up-regulation of early visual cortical processing is associated with an enhanced target saliency while learning visual search tasks.
Meeting abstract presented at VSS 2015