Spatial vision thresholds in the near absence of attention.

It is well known that attention increases the discriminability of some types of spatial information. To ascertain more specifically which types of spatial information benefit from attention, we have measured spatial vision thresholds both in the presence and in the near absence of attention. To obtain near absence of attention, we induce subjects to focus attention elsewhere in the display by means of a suitably demanding concurrent visual task. We measure contrast and orientation thresholds for sine-wave gratings, as well uni- and bidirectional offset thresholds for vernier targets. The results suggest that attention selectively lowers some thresholds but not others: orientation thresholds are far more affected than contrast thresholds, and bidirectional vernier thresholds are far more affected than unidirectional thresholds.