3 Project 2 – Spatial cue-priming effects on accuracy in signal detection tasks
3.3 Summary of Project 2
In Project 2, spatial cue-priming was transferred to a signal detection task. This task is more indicative of attentional processes at early levels of processing than the letter discrimination task in Project 1. Attentional effects in similar signal detection tasks have been taken as evidence for early selection. Primes and cues were similar to Project 1 with squares cueing the left side and diamonds cueing the right side of fixation. On each trial participants had to indicate whether a small white dot had been presented or not. The dot could be presented on top of a black square either to the left or to the right of fixation and its detection
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was made difficult by the presence of two random line masks which were presented immediately after target offset, one at each side. The relevant side on each trial was predicted with 100% validity by a cue symbol which was again preceded by a masked prime symbol. It has been argued that cueing effects on accuracy in detection tasks reflect early selection, because they cannot easily be explained at later decisional stages of processing. We used rather long cue-target SOAs because results of preliminary experiments suggested that priming effects might be larger with long cue-target SOAs, a finding that is consistent with findings from Luck and colleagues (1996) who suggested that cueing effects based on allocation of attentional resources require longer cue-target SOAs than cueing effects based on other processes such as reduction of spatial uncertainty. In Experiment 4, we found priming effects on detection accuracy which increased with prime-cue SOA. Due to the fact that there was confoundation of prime-cue SOA and cue-target SOA (prime-target SOA was held constant at 400 ms) priming effects also decreased with increasing cue-target SOA.
Therefore, we cannot be certain whether the effect of SOA on priming effects was caused by varying prime-cue SOA, varying cue-target SOA or both. Nevertheless, variation of priming effects with SOA was similar as in Project 1. In Experiment 6 we attempted to disentangle the effects of prime-cue SOA and cue-target SOA while at the same time improving masking of primes. To this end we varied cue-target SOA while keeping prime-cue SOA constant. In addition we increased masking by using star shaped mask stimuli instead of square and diamond stimuli and by presenting the primes randomly at one of two possible locations.
However, in Experiment 6 there were no priming effects on target recognition performance.
As we made several changes from Experiment 4 to Experiment 6, there are several explanations for this absence. We speculated that, apart from the changes in prime and cue stimuli which had successfully reduced prime visibility, the introduction of long cue-target SOAs might have reduced participants’ attention to cues. To test this hypothesis we
Project 2 – Spatial cue-priming effects on accuracy in signal detection tasks
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conducted a third experiment. In Experiment 7 we used the same prime and cue stimuli as in Experiment 6 combined with the same SOAs as in Experiment 4. Here, again, priming effects were absent which suggests that some attribute of primes and cues is critical for cue-priming effects on signal detection. Compared to the simple square and diamond stimuli in Experiment 4, the more complex combined square/diamond-and-star stimuli in Experiments 6 and 7 led to decreased visibility of primes, a smaller amount of attention devoted to the critical prime’s location and decreased perceptual similarity between symbols presented at the same location.
From previous cue-priming experiments (Mattler, 2006) as well as Project 1 it seems that perceptual similarity leads to larger priming effects. With this in mind, we conducted Experiment 5, applying the same logic as in Experiment 3 (Project 1) to spatial cue-priming signal detection. In Project 2 we used the same symbols as primes and cues in Experiment 4 whereas in Experiments 6 and 7 there were no trials on which prime and cue were the same symbol configuration as the location of the relevant symbol always differed. Thus, it might be that priming effects in signal detection tasks can be explained solely on basis of perceptual priming of cue processing. If this is the case, priming effects on signal detection should only be present when prime and cue are the same symbol but not when they are only associated to the same side and perceptually dissimilar. This pattern is exactly what we found in Experiment 5 which suggests that prime processing does not extend beyond perceptual stages in a signal detection task, when attention operates at early stages of target processing.
In summary, priming effects on signal detection can be found but seem to be entirely explainable as resulting from perceptual priming of cue processing. This shows that access for masked stimuli to attentional processes at early stages of processing is limited compared to the access to attentional processes relevant in the letter discrimination task in Project 1. In
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addition to an increase in accuracy in signal detection tasks, evidence for early selection by spatial attention has been provided by experiments that studied physiological markers of attentional selection. This approach was applied to spatial cue-priming in Project 3.
Project 3 - Spatial cue-priming effects on physiological measures of target processsing
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