Fast noninertial shifts of attention.

It was suggested that some discrimination tasks (e.g. discrimination between the letters T and L) require serial search by scrutinizing each letter (target) with a small aperture of focal attention. Here we examine the effect of intertarget distance on discrimination performance, using two targets. We find reduction in performance at short distances, in agreement with masking studies, but constant performance independent of distance outside this masking region. This constant performance is still lower than expected from masking effects and might reflect attentive process. Sequential presentation of the targets with delays up to 30-40 ms, while reducing available processing time, does not cause reduction in performance, thus supporting the suggestion that discrimination of the two targets is a serial process. The independence of performance on distance suggests fast noninertial shifts of attention.