Crosstalk between on-line and off-line processing of visual features.

Three dual-task experiments were conducted to investigate the relation between immediate, "on-line" judgments about visual features and delayed, "off-line" judgments. One hypothesis ("selective interference") predicted that dual-task performance would be challenged specifically within a visual dimension, as both tasks compete for the same resources. Another hypothesis ("cost of switching") made the opposite prediction. In Experiment 1, participants performed either color or shape discriminations in the on-line and off-line visual tasks, with systematic variation of feature similarity between the on-line and off-line features. In Experiment 2, participants performed either color or shape discriminations in the off-line task and color discriminations in the on-line task, with no overlap between the on-line and off-line features. In Experiment 3, participants performed color discriminations in both the on-line and off-line tasks, with partially overlapping stimulus sets. Altogether, the data from the three experiments provided evidence in favor of the hypothesis of cost of switching. Stimulus-stimulus compatibility effects between features in the off-line task and those in the on-line task further underscored the perceptual nature of the crosstalk.