DO PERIPHERAL NON-INFORMATIVE CUES INDUCE EARLY FACILITATION OF TARGET DETECTION

It has been reported that simple reaction time (RT) to a peripheral vi sual target is faster if the target is presented within about 200 msec from the onset of a non-informative cue flashed at the same location, as compared with RT to a target presented at an uncued location. This period of facilitation is followed by a period of inhibition during w hich RT is longer if cue and target are shown at the same location or at different locations within the same hemifield, as opposed to contra lateral cues and targets. Early facilitation has been explained by an automatic covert orienting towards the cue, while the following inhibi tion has been regarded as a consequence of such covert orienting. In a series of four experiments, we have investigated the dependency of th ese effects on the temporal and spatial relationships between cue and target. Normal, right-handed subjects responded to a target displayed for 16 msec simultaneously with, or following at stimulus-onset asynch ronies (SOAs) of 60, 130, 300 or 900 msec, the onset of a non-informat ive cue. Both cues and targets could appear at random in one of four l ocations (Expts 1-3) or in one of two locations (Expt 4) disposed symm etrically across the fixation point along the horizontal meridian. Dur ation of the cue varied between experiments. In Expt 1 it was 16 msec. In Expt 2 the cue remained on view throughout the period of the SOA a nd terminated 300 msec after target onset. In the remaining two experi ments cue duration was 130 msec. In the first experiment, at all cue-t arget SOAs RTs to targets flashed either at the same location or in th e same hemifield as the cue were significantly slower than RTs to cont ralateral cue-target combinations (RT inhibition). In the other experi ments, there was no RT inhibition with targets in cued locations if th e cue remained on during target presentation and outlasted target offs et. Since at no SOA was RT to targets in cued locations shorter than R T to targets contralateral to cues, there was no direct evidence for f acilitation. However, the facilitatory influence of these cues could b e inferred from the fact that they countered and masked inhibition. RT to uncued targets ipsilateral to cues was consistently inhibited in a ll experimental conditions. These results show that at each cue-target SOA the consequences of a peripheral non-informative cue depend on wh ether or not the cue remains visible during target processing. Further , our findings suggest that facilitation of RT to targets in cued posi tions, if any, does not precede and cause inhibition, but co-occurs wi th it.