Abstract
In a typical pop-out task, there is one target and a varying number of distractor stimuli. Now imagine a target-absent display in the context of a pop-out task: all items are identical, and it is decidedly easy to conclude that all items in the display are distractors, precisely because there is no target to select on that display. One may be tempted to say that, as far as the attention system is concerned, these two types of distractors are the same: target-present distractors and target-absent distractors. The present study proposes that this is actually not the case. Target-absent distractors can sometimes produce inter-trial effects that their close-cousins, the target-present distractors, cannot. We used a letters/numbers categorical oddball task to demonstrate this difference. The results are interpreted in the context of recent findings in cognitive neuroscience as well as cognitive modeling.
Highlights
There has been substantial interest in studying inter-trial effects in visual search experiments in which there is uncertainty as to what the target might be on the trial
The average search slope for letters amongst numbers was 3.6 ms/item. These results are consistent with the hypothesis that letters pop-out amongst numbers
Participants were more accurate on trials with letter targets (96.5%) than with number targets (94.8%), F(1,18) = 9.10, p = 0.007
Summary
There has been substantial interest in studying inter-trial effects in visual search experiments in which there is uncertainty as to what the target might be on the trial. In oddball experiments, participants must quickly decide which item is the visual oddball and make a response to it, such as saccade toward it (e.g., Becker, 2008; Caddigan and Lleras, 2010; Tseng et al, 2014), or respond to some attribute of the oddball that requires the target be scrutinized to some degree (e.g., Maljkovic and Nakayama, 1994; Ariga and Kawahara, 2004; Goolsby et al, 2005; Kristjánsson and Driver, 2008; Lamy et al, 2008; Lleras et al, 2008). Some of the initial interest in these oddball search inter-trial effects came from the following apparent contradiction: if the oddball is a pop-out (and by that we understood a stimulus with sufficient bottomup salience as to capture attention automatically onto itself), why should there be any inter-trial effects in an oddball task at all? How can an automatic pre-attentive computation, such as the detection and automatic orienting toward of a pop-out, be improved upon by simple repetition?
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