Investigating the Role of Left Parietal Cortex in Real-World Visual Search Tasks: A Replication Study Using Transcranial Direct Current Stimulation (tDCS)
Visual search is a cognitive process in which we locate a target object among similar distractors. This process is crucial for many everyday tasks, such as security X-ray screening, where the goal is to identify dangerous objects hidden in a cluttered background. However, existing theories of visual search are mainly based on lab-based studies, which do not always transfer to real-world scenarios.
The right parietal cortex is known to play a crucial role in visual search tasks, but the role of the left parietal cortex in disembedding targets from their background is less well-established. To address this gap, a pilot study was conducted to investigate the effects of non-invasive brain stimulation over the left posterior parietal cortex (PPC) on novice performance in X-ray screening tasks. The findings suggested that anodal left PPC stimulation improved novice performance, in line with previous brain imaging studies.
However, the efficacy of transcranial direct current stimulation (tDCS), the brain stimulation technique used in the study, is under question, with many failed replications. To re-test the hypothesis, a within-subjects study was conducted, comparing the effects of left-side parietal stimulation, right-side parietal stimulation, and low-intensity sham stimulation on novice performance in X-ray screening tasks. The pre-registered analysis did not detect any significant differences between the different stimulation conditions on performance. Exploratory analyses also showed no effects on other indices of performance or a disembedding control task.
The results of this study raise concerns about the current lack of optimal control conditions and highlight the need for replication in the field. Alternative stimulation techniques or multi-technique approaches may be needed to establish the causal link between the left parietal cortex and disembedding performance. Furthermore, low-intensity sham stimulation was found to be ineffective for blinding participants in a within-subjects design, highlighting the need for more robust control conditions.
In conclusion, further research is needed to better understand the role of the left parietal cortex in real-world visual search tasks and to determine the efficacy of tDCS in improving performance. This knowledge can have important implications for the development of effective training and rehabilitation programs for individuals with visual search impairments.
Reference Paper
Wagner, J. et al. (2020) “Effects of transcranial direct current stimulation over the posterior parietal cortex on novice x-ray screening performance,”
Cortex, 132, pp. 1–14.
Available at: https://doi.org/10.1016/j.cortex.2020.08.002.