title: Exploring the impact of target eccentricity and task difficulty on covert visual spatial attention and its implications for brain computer interfacing.
abstract: OBJECTIVE
  Covert visual spatial attention is a relatively new task used in brain computer interfaces (BCIs) and little is known about the characteristics which may affect performance in BCI tasks. We investigated whether eccentricity and task difficulty affect alpha lateralization and BCI performance.
  
  
  METHODS
  We conducted a magnetoencephalography study with 14 participants who performed a covert orientation discrimination task at an easy or difficult stimulus contrast at either a near (3.5°) or far (7°) eccentricity. Task difficulty was manipulated block wise and subjects were aware of the difficulty level of each block.
  
  
  RESULTS
  Grand average analyses revealed a significantly larger hemispheric lateralization of posterior alpha power in the difficult condition than in the easy condition, while surprisingly no difference was found for eccentricity. The difference between task difficulty levels was significant in the interval between 1.85 s and 2.25 s after cue onset and originated from a stronger decrease in the contralateral hemisphere. No significant effect of eccentricity was found. Additionally, single-trial classification analysis revealed a higher classification rate in the difficult (65.9%) than in the easy task condition (61.1%). No effect of eccentricity was found in classification rate.
  
  
  CONCLUSIONS
  Our results indicate that manipulating the difficulty of a task gives rise to variations in alpha lateralization and that using a more difficult task improves covert visual spatial attention BCI performance. The variations in the alpha lateralization could be caused by different factors such as an increased mental effort or a higher visual attentional demand. Further research is necessary to discriminate between them. We did not discover any effect of eccentricity in contrast to results of previous research.
authors: Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands.
authors: Linsey
authors: L
authors: Roijendijk
authors: Jason
authors: J
authors: Farquhar
authors: Marcel
authors: M
authors: van Gerven
authors: Ole
authors: O
authors: Jensen
authors: Stan
authors: S
authors: Gielen
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology*; D062207:Brain-Computer Interfaces; D005260:Female; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods; D008297:Male; D011340:Problem Solving / Q000502:physiology*; D013037:Spatial Behavior / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*