Memory precision for salient distractors decreases with learned suppression

Attention operates as a cognitive gate that selects sensory information for entry into memory and awareness (Driver, 2001, British Journal of Psychology, 92, 53–78). Under many circumstances, the selected information is task-relevant and important to remember, but sometimes perceptually salient nontarget objects will capture attention and enter into awareness despite their irrelevance (Adams & Gaspelin, 2020, Attention, Perception, & Psychophysics, 82[4], 1586–1598). Recent studies have shown that repeated exposures with salient distractor will diminish their ability to capture attention, but the relationship between suppression and later cognitive processes such as memory and awareness remains unclear. If learned attentional suppression (indicated by reduced capture costs) occurs at the sensory level and prevents readout to other cognitive processes, one would expect memory and awareness to dimmish commensurate with improved suppression. Here, we test this hypothesis by measuring memory precision and awareness of salient nontargets over repeated exposures as capture costs decreased. Our results show that stronger learned suppression is accompanied by reductions in memory precision and confidence in having seen a color singleton at all, suggesting that such suppression operates at the sensory level to prevent further processing of the distractor object.

The Malleability of Attentional Capture

We suggest that consideration of trial-by-trial variations, individual differences, and training data will enrich the current framework in Luck et al. (2020). We consider whether attentional capture is modulated by trial-by-trial fluctuations of attentional state and experiences on the previous trial. We also consider whether individual differences may affect attentional capture while highlighting potential challenges in using the color-singleton task to measure individual differences. Finally, performance in the color-singleton task can be modified dramatically with practice but the underlying mechanisms are not entirely clear. Understanding the malleability of attentional capture may broaden the current framework and resolve outstanding questions. The version of record of this manuscript will be available in Visual Cognition (2021), https://doi.org/10.1080/13506285.2021.1915903

Changes in visual cortical processing attenuate singleton distraction during visual search

The ability to suppress distractions is essential to successful completion of goal-directed behaviors. Several behavioral studies have recently provided strong evidence that learned suppression may be particularly efficient in reducing distractor interference. Expectations about a distractor’s repeated location, color, or even presence is rapidly learned and used to attenuate interference. In this study, we use a visual search paradigm in which a color singleton, which is known to capture attention, occurs within blocks with high or low frequency. The behavioral results show reduced singleton interference during the high compared to the low frequency block (Won et al., 2019). The fMRI results provide evidence that the attenuation of distractor interference is supported by changes in singleton, target, and non-salient distractor representations within retinotopic visual cortex. These changes in visual cortex are accompanied by findings that singleton-present trials compared to non-singleton trials produce greater activation in bilateral parietal cortex, indicative of attentional capture, in low frequency, but not high frequency blocks. Together, these results suggest that the readout of saliency signals associated with an expected color singleton from visual cortex is suppressed, resulting in less competition for attentional priority in frontoparietal attentional control regions.

Enhancement and Suppression Flexibly Guide Attention

Previous research suggests that observers can suppress salient-but-irrelevant stimuli in a top-down manner. However, one question left unresolved is whether such suppression is, in fact, solely due to distractor-feature suppression or whether it instead also reflects some degree of target-feature enhancement. The present study ( N = 60) addressed this issue. On search trials (70% of trials), participants searched for a shape target when an irrelevant color singleton was either present or absent; performance was better when a color singleton was present. On interleaved probe trials (30% of trials), participants searched for a letter target. Responses were faster for the letter on a target-colored item than on a neutral-colored item, whereas responses were slower for the letter on a distractor-colored item than on a neutral-colored item. The results demonstrate that target-feature enhancement and distractor-feature suppression contribute to attentional guidance independently; enhancement and suppression flexibly guide attention as the occasion demands.

Evidence for second-order singleton suppression based on probabilistic expectations

Decades of research in attention have shown that salient distractors (e.g., a color singleton) tend to capture attention. However, in most studies, singleton distractors are just as likely to be present as absent. We therefore have little knowledge of how probabilistic expectations of the salient distractor's occurrence and features affect suppression. In three experiments, we explored this question by manipulating the frequency of a singleton distractor and the variability of its color within a search display. We found that increased expectations regarding the occurrence of the singleton distractor eliminated the singleton RT cost and reduced the number of first saccades to the singleton. In contrast, expectations regarding variability in the singleton color did not affect singleton capture. This was surprising and suggests the ability to suppress second order salience over and above that of first order features. We next inserted the probe display that included a to-be-reported letter inside each shape between search trials to measure if attention went to multiple objects. The letter in the singleton location was reported less often in the high frequency condition, suggesting proactive suppression of expected singleton. Additionally, we found that trial-to-trial repetitions of a singleton (irrespective of its color and location) facilitated performance (i.e., singleton repetition priming), but repetitions of its specific color or location did not. Together our findings demonstrate that attentional capture by a color singleton distractor is attenuated by probabilistic expectations of its occurrence, but not of its color and location.

Inhibition of Return after Color Singletons

Inhibition of return (IOR) is the faster selection of hitherto unattended than previously attended positions. Some previous studies failed to find evidence for IOR after attention capture by color singletons. Others, however, did report IOR effects after color singletons. The current study examines the role of cue relevance for obtaining IOR effects. By using a potentially more sensitive method – saccadic IOR – we tested and found IOR after relevant color singleton cues that required an attention shift (Experiment 1). In contrast, irrelevant color singletons failed to produce reliable IOR effects in Experiment 2. Also, Experiment 2 rules out an alternative explanation of our IOR findings in terms of masking. We discuss our results in light of pertaining theories of IOR.