Abrupt Onsets Cannot Be Ignored

Article excerpt

Participants identified target letters at cued locations in the presence of occasional abrupt onsets of new distractor letters. The onsets distracted the participants and impaired their letter identification performance despite confirmation that they were using the information provided by the cue. This result contrasts with earlier results found by other researchers that revealed an ability of participants to ignore abrupt onsets in some cases. Our results, however, were obtained under conditions that prevented anticipatory eye movements to the target. In a subsequent experiment when participants were permitted to look at the target in advance, the distracting effect of the onsets was eliminated, suggesting that participants may have looked at the target in the earlier studies. We conclude that abrupt onsets cannot be ignored unless the target element receives a substantial advantage via fixation.

Researchers interested in stimulus-driven attentional capture have found that the appearance of an abrupt onset is one of the few stimuli that seem to capture attention even in the absence of a top-down expectation. For example, Irwin, Colcombe, Kramer, and Hahn (2000) found that participants were 51 msec slower to identify target letters when an irrelevant onset appeared in the display, suggesting that abrupt onsets diverted attentional resources from the letter identification task. Nevertheless, even abrupt onset appearance does not satisfy the "resistance to suppression" criterion of stimulus-driven capture. That criterion is satisfied only when an observer is unable to suppress the effects of a particular stimulus under any circumstance. Two laboratories (Theeuwes, 1991; Yantis & Jonides, 1990) have shown that it is possible for participants to successfully ignore abrupt onsets under some circumstances. To date, only motion onsets appear unable to be suppressed (Christ & Abrams, 2005).

It is worth noting that the few studies mentioned that have explored the ability to ignore abrupt onsets did so under conditions in which participants were free to move their eyes around the display.1 As a result, because participants were provided with mostly valid cues to the target's location, it is possible that on some or most of the trials in the experiments, participants chose to fixate the target in advance. If participants fixated the target, they could benefit from the greater resolution at the fovea, and they would also be able to focus attention very narrowly on the target region. Under such conditions, the ability to ignore the appearance of an abrupt onset in the periphery would not seem so surprising. In the present study, we reexamined the ability of participants to ignore abrupt onsets while their eye positions were monitored. To anticipate the results: We found that participants are not capable of ignoring abrupt onsets when forced to maintain fixation at the center of the display.

EXPERIMENT 1

In our first experiment, we asked the participants to identify letters that appeared in a prespecified location while, on some trials, a new letter appeared in a nontarget location. During the experiment, the participants' eye positions were monitored to ensure that they remained fixated at the center of the display prior to presentation of the target. If indeed participants can ignore abrupt onsets when the target location is known, then we should obtain the same results here that were obtained by earlier researchers (Theeuwes, 1991; Yantis & Jonides, 1990) who examined this issue, but without eye position monitoring.

Method

Participants. Eleven experimentally naive undergraduate students served as participants in a single 40-min session in exchange for course credit. All had normal or corrected-to-normal vision.

Apparatus and Procedure. The participants were seated 34 in. (86.4 cm) from a CRT display in a dim, sound-attenuated room. Each trial began with a preview display that consisted of a small centrally located pointer and three figure-eight placeholders. …

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