Can Hand Position Enhance Target Detection in a Complex, Real-World Visual Search Task?

Previous research has shown that holding, or placing one’s hands near, an object can alter visual processing of that object in a variety of ways, including enhancing the detection of change, reducing the effect of distraction, and boosting sensitivity to low-spatial frequency information. These studies have mostly used abstract laboratory cuing and search paradigms to demonstrate a near-hands advantage. In the current study we explored whether enhanced visual analysis in the space near one’s hands confers an advantage when applied to a real-world visual search task. We asked participants to search for knives in X-ray images of luggage (a TSA baggage screening task). Stimuli were presented on a tablet computer. In one experiment participants performed the task by pressing response boxes at the edge of the screen, which forced them to grip the display within their hands. Alternatively, they responded with button press on a mouse held within their lap. There was no effect of hand placement on speed or accuracy. In a second experiment, participants were asked to use their finger to trace along the image of the bag to ensure that all potential target locations were inspected. In addition to any effect of hand proximity to the target, it was anticipated that this strategy would encourage a more systematic search strategy, potentially improving accuracy. Participants inspected bags substantially longer when using this strategy (1,238 ms longer for target present trials, 2,590 ms for target absent trials). Interestingly, this additional time spent viewing the image did not result in improved accuracy. While basic research suggests that hand proximity can influence visual processing, these benefits may not scale-up to more complex search situations.