Abstract
In a previous study on eye movements during a search task (Leonard et al., 2018), participants with longer first saccade latencies (FSLs) tended to find a contour target with fewer saccadic eye movements (SEMs) than those who had shorter FSLs. Here we asked whether these individual differences were amenable to manipulation, and whether increasing an individual’s FSL would improve search efficiency. Forty-eight undergraduates completed a search task in three blocks. The first block was a “neutral condition”, where target location was random. Counterbalanced “central” and “peripheral” bias blocks followed. In the central-bias block, 75% of targets appeared within a 4-degree radius, and the remaining 25% appeared outside a 6-degree radius. The inverse occurred in the peripheral-bias block. Generalized linear mixed modeling assessed population-level (“fixed”) effects and individual differences (“random” effects) for FSL and search efficiency (i.e., SEM count). Regarding FSLs, significant main effects were found for block and target eccentricity. FSLs in central and neutral blocks were significantly shorter than in the peripheral-bias block. A negative slope was found for target eccentricity when targets appeared within the central window, which was significantly steeper in the peripheral-bias block. Random effects tests revealed that participants with long FSLs in the neutral block were more likely to lengthen FSLs for central targets during the central-bias block, suggesting they engaged in more covert exploration before making an SEM. The association between longer FSLs and search efficiency was replicated, however increasing target eccentricity attenuated this effect. Target eccentricity also interacted with block, where long eccentricities increased SEMs in the neutral and central-bias blocks, but significantly less so in the peripheral-bias block. The lack of meaningful random effects correlations indicated that changing FSL does not improve search efficiency. We conclude that individual differences in FSL may be due to intrinsic attentional control and processing speed abilities.