Individual differences in object-based attention effects in discrimination and detection tasks

Abstract

It has been long suggested that attention can be allocated to both space and objects. Previously, Roggeveen et al. (VSS 2008) used a target discrimination task (Moore, Yantis, & Vaughan, 1998) to investigate individual differences in object-based attention (OBA) for both vertical and horizontal objects. Interestingly, although we found evidence of space based attention in both orientations, we found OBA only for horizontal objects. One limitation of Roggeveen's study is that only discrimination tasks were tested, while most OBA research has focused on detection. Here we directly compare results for 60 observers tested in tasks involving both target discrimination and target detection (Egly, Driver, & Rafal, 1994). In general, RTs were much shorter for the detection task. For target discrimination we found the same pattern of results as described before: OBA for horizontal objects and opposite effects for vertical ones. For target detection, OBA was more pronounced for horizontal objects, but the trend was in the same direction for vertical objects. These results underline orientation effects may exist in multiple tasks, and that OBA is generally stronger for horizontal objects. Previous research has suggested that performance in a variety of visual tasks is better on the horizontal than the vertical meridian (e.g., Carrasco Talgar, Cameron, 2001). Such attentional preferences could explain why OBA in the current study was generally more pronounced for horizontal objects. Finally, given our large sample size, we were able to use bootstrapping to estimate effect sizes for individual subjects. We found high degrees of variability among subjects across both tasks and orientations. Whereas more than 80% of observers exhibited significant space-based attention effects, fewer than 10% of the observers in each task and orientation showed significant OBA. Taken as a whole, these results suggest that OBA might not be as robust and ubiquitous as previously assumed.

This work was supported by grants from the Canada Research Chair Program to A.B.S. and P.J.B., the Alexander von Humboldt Foundation to K.S.P., and the Alexander Graham Bell Canada Graduate Scholarship to E.R.