Oculomotor capture by colour singletons depends on intertrial priming

Temporal integration of feature probability distributions

Humans are surprisingly good at learning the statistical characteristics of their visual environment. Recent studies have revealed that not only can the visual system learn repeated features of visual search distractors, but also their actual probability distributions. Search times were determined by the frequency of distractor features over consecutive search trials. The search displays applied in these studies involved many exemplars of distractors on each trial and while there is clear evidence that feature distributions can be learned from large distractor sets, it is less clear if distributions are well learned for single targets presented on each trial. Here, we investigated potential learning of probability distributions of single targets during visual search. Over blocks of trials, observers searched for an oddly colored target that was drawn from either a Gaussian or a uniform distribution. Search times for the different target colors were clearly influenced by the probability of that feature within trial blocks. The same search targets, coming from the extremes of the two distributions were found significantly slower during the blocks where the targets were drawn from a Gaussian distribution than from a uniform distribution indicating that observers were sensitive to the target probability determined by the distribution shape. In Experiment 2, we replicated the effect using binned distributions and revealed the limitations of encoding complex target distributions. Our results demonstrate detailed internal representations of target feature distributions and that the visual system integrates probability distributions of target colors over surprisingly long trial sequences.

Effects of Mindset and Dietary Restraint on Attention Bias for Food and Food Intake

Evidence for attention bias (AB) for food in restrained eaters is inconsistent. A person's mindset related to food - that is, whether someone focuses on the hedonic or health aspects of food - might be an overlooked influence on AB for food, possibly explaining the inconsistency in the literature. Fluctuations between a hedonic versus a health mindset might be strongest in restrained eaters, who have a conflicted relationship with food. We investigated the effect of mindset and dietary restraint on AB for food and food intake. We hypothesized that AB for food, as reflected in eye-movement measures and manual response latencies, as well as food intake, would be larger in the hedonic than in the health mindset, most strongly in participants scoring high on dietary restraint. Moreover, we expected a positive correlation between AB for food and food intake, especially in the hedonic mindset. We used short video clips to induce either a health or hedonic mindset. Subsequently, participants (n = 122) performed a modified additional singleton task with pictures of high-caloric food vs neutral pictures as irrelevant distractors. Next, food intake was measured in a bogus taste test. We found no evidence for an AB towards food, nor any moderation by either mindset or dietary restraint. Food intake tended to be higher for participants scoring higher on dietary restraint, but effects were not moderated by mindset. Response-latency based AB for food tended to correlate positively with food intake in the hedonic mindset. Taken together, our hypotheses regarding AB for food were largely not confirmed. We provide suggestions on how to improve upon the specific implementations of our AB task and mindset manipulation, to strengthen future research in this field.

Priming effects in inefficient visual search: Real, but transient

In visual search tasks, responses to targets on one trial can influence responses on the next trial. Most typically, target repetition speeds response while switching to a different target slows response. Such "priming" effects have sometimes been given very significant roles in theories of search (e.g., Theeuwes, Philosophical Transactions of the Royal Society B: Biological Sciences, 368, 1628, 2013). Most work on priming has involved "singleton" or "popout" tasks. In non-popout priming tasks, observers must often perform a task-switching operation because the guiding template for one target (e.g., a red vertical target in a conjunction task) is incompatible with efficient search for the other target (green horizontal, in this example). We examined priming in inefficient search where the priming feature (Color: Experiments 1-3, Shape: Experiments 4-5) was irrelevant to the task of finding a T among Ls. We wished to determine if finding a red T on one trial helped observers to be more efficient if the next T was also red. In all experiments, we found additive priming effects. The reaction time (RT) for the second trial was shorter if the color of the T was repeated. However, there was no interaction with set size. The slope of the RT × Set Size function was not shallower for runs of the same target color, compared to trials where the target color switched. We propose that priming might produce transient guidance of the earliest deployments of attention on the next trial or it might speed decisions about a selected target. Priming does not appear to guide attention over the entire search.

Covert attention is attracted to prior target locations: Evidence from the probe paradigm

There is growing evidence that visual attention can be guided by selection history. One example of this is intertrial location priming, whereby attention is attracted to the target location from the previous trial. Most previous demonstrations of location priming have relied on manual response time effects whereby search is speeded when the target location repeats from the previous trial. However, these latency-based effects have recently been challenged as being due to response facilitation that occurs after the target has been found, rather than an attentional bias toward the previous target location. To resolve this, the current study used a probe paradigm to assess whether covert attention is biased to the previous-trial target location. On search trials, participants searched for a specific target shape amongst distractor shapes and made a speeded response to the location of a dot inside the target. On probe trials, letters briefly appeared at each search location and after a delay, participants were asked to report as many letters as possible. Probe report accuracy was used to assess the likelihood that a given location was attended. Three experiments indicated that probe report accuracy was greatly improved for letters at the previous-trial target location compared with baseline levels. Importantly, this occurred even when strong attentional guidance to the target was encouraged and even when a nontarget stimulus appeared at the primed location. Altogether, the results suggest that covert attention is strongly attracted to the previous target location during visual search.

Inhibition continues to guide search under concurrent visual working memory load

It is well known that attention can be automatically attracted to salient items. However, recent studies show that it is possible to avoid distraction by a salient item (with a known feature), leading to facilitated search. This article tests a proposed mechanism for distractor inhibition: that a mental representation of the distractor feature held in visual working memory (VWM) allows attention to be guided away from the distractor. We tested this explanation by examining color-based inhibition in visual search for a shape target with and without VWM load. In Experiment 1 the presence of a distractor facilitated visual search under low and high VWM loads, as reflected in faster response times when the distractor was present (compared to absent), and in fewer eye movements to the salient distractor than the non-target items. However, the eye movement inhibition effect was noticeably weakened in the load conditions. Experiment 2 explored further, to distinguish between inhibition of the distractor color and activation of the (irrelevant) target color. Intermittently presenting single-color search trials that contained only either a target, distractor or a neutral-colored singleton revealed that the distractor color attracted attention less than the neutral color with and without VWM load. The target color, however, only attracted attention more than neutral colors under no load, whereas a VWM load completely eliminated this effect. This suggests that although VWM plays a role in guiding attention to the (irrelevant) target color, distractor-feature inhibition can operate independently.

Does feature intertrial priming guide attention? The jury is still out

Our search performance is strongly influenced by our past experience. In the lab, this influence has been demonstrated by investigating a variety of phenomena, including intertrial priming, statistical learning, and reward history, and collectively referred to as selection history. The resulting findings have led researchers to claim that selection history guides attention, thereby challenging the prevailing dichotomy, according to which top-down and bottom-up factors alone determine attentional priority. Here, we re-examine this claim with regard to one selection-history phenomenon, feature intertrial priming (aka priming of pop-out). We evaluate the evidence that specifically pertains to the role of feature intertrial priming in attentional guidance, rather than in later selective processes occurring after the target is found. We distinguish between the main experimental rationales, while considering the extent to which feature intertrial priming, as studied through different protocols, shares characteristics of top-down attention. We show that there is strong evidence that feature intertrial priming guides attention when the experimental protocol departs from the canonical paradigm and encourages observers to maintain the critical feature in visual working memory or to form expectations about the upcoming target. By contrast, the current evidence regarding the standard feature intertrial priming phenomenon is inconclusive. We propose directions for future research and suggest that applying the methodology used here in order to re-evaluate of the role of other selection history phenomena in attentional guidance should clarify the mechanisms underlying the strong impact of past experience on visual search performance.

Template-to-distractor distinctiveness regulates visual search efficiency

All models of attention include the concept of an attentional template (or a target or search template). The template is conceptualized as target information held in memory that is used for prioritizing sensory processing and determining if an object matches the target. It is frequently assumed that the template contains a veridical copy of the target. However, we review recent evidence showing that the template encodes a version of the target that is adapted to the current context (e.g. distractors, task, etc.); information held within the template may include only a subset of target features, real world knowledge, pre-existing perceptual biases, or even be a distorted version of the veridical target. We argue that the template contents are customized in order to maximize the ability to prioritize information that distinguishes targets from distractors. We refer to this as template-to-distractor distinctiveness and hypothesize that it contributes to visual search efficiency by exaggerating target-to-distractor dissimilarity.

Oculomotor Inhibition of Salient Distractors: Voluntary Inhibition Cannot Override Selection History

Several studies have demonstrated that salient distractors can be proactively inhibited to prevent attentional capture. Traditional theories frame attentional guidance effects such as this in terms of explicit goals. However, several researchers have recently argued that that unconscious factors-such as the features of attended and ignored items on previous trials (called selection history)-play a stronger role in guiding attention and can overpower explicit goals. The current study assessed whether voluntary inhibition can overpower selection history. We directly compared both forms of top-down control by measuring the control of eye movements, which offer an unambiguous measure of which location has won the competition for attention. We repeatedly found that selection history overpowered any effects of voluntary goals, such that observers were unable to avoid fixating a salient distractor of a known color if the target had been presented in that color on the previous trial. Moreover, a salient distractor of a particular color captured gaze even when the observer had voluntarily chosen this color to be the distractor color just moments before. Taken together, these experiments suggest that the ability to inhibit a salient color singleton is primarily a result of recent experience and not a result of explicit goals.

Distinguishing among potential mechanisms of singleton suppression

Previous research has revealed that people can suppress salient stimuli that might otherwise capture visual attention. The present study tests between 3 possible mechanisms of visual suppression. According to first-order feature suppression models, items are suppressed on the basis of simple feature values. According to second-order feature suppression models, items are suppressed on the basis of local discontinuities within a given feature dimension. According to global-salience suppression models, items are suppressed on the basis of their dimension-independent salience levels. The current study distinguished among these models by varying the predictability of the singleton color value. If items are suppressed by virtue of salience alone, then it should not matter whether the singleton color is predictable. However, evidence from probe processing and eye movements indicated that suppression is possible only when the color values are predictable. Moreover, the ability to suppress salient items developed gradually as participants gained experience with the feature that defined the salient distractor. These results are consistent with first-order feature suppression models, and are inconsistent with the other models of suppression. In other words, people primarily suppress salient distractors on the basis of their simple features and not on the basis of salience per se. (PsycINFO Database Record

Top-down knowledge modulates onset capture in a feedforward manner

How do we select behaviourally important information from cluttered visual environments? Previous research has shown that both top-down, goal-driven factors and bottom-up, stimulus-driven factors determine which stimuli are selected. However, it is still debated when top-down processes modulate visual selection. According to a feedforward account, top-down processes modulate visual processing even before the appearance of any stimuli, whereas others claim that top-down processes modulate visual selection only at a late stage, via feedback processing. In line with such a dual stage account, some studies found that eye movements to an irrelevant onset distractor are not modulated by its similarity to the target stimulus, especially when eye movements are launched early (within 150-ms post stimulus onset). However, in these studies the target transiently changed colour due to a colour after-effect that occurred during premasking, and the time course analyses were incomplete. The present study tested the feedforward account against the dual stage account in two eye tracking experiments, with and without colour after-effects (Exp. 1), as well when the target colour varied randomly and observers were informed of the target colour with a word cue (Exp. 2). The results showed that top-down processes modulated the earliest eye movements to the onset distractors (<150-ms latencies), without incurring any costs for selection of target matching distractors. These results unambiguously support a feedforward account of top-down modulation.

Oculomotor capture by irrelevant onsets with and without color contrast

It is widely known that irrelevant onsets (i.e., items appearing in previously empty locations) can automatically capture attention and attract our gaze. Some studies have shown that onset capture is stronger when the onset distractor matches the target feature, indicating that onset capture can be modulated by feature-based (top-down) tuning to the target. However, it is less clear whether and to what extent the perceptual saliency of the distractor can further modulate this effect. This study examined the effects of target similarity, competition between target and distractor, and bottom-up color contrast on the ability of onset distractor to capture the gaze, by varying the color (contrast) and stimulus-onset asynchrony of the onset distractor. The results clearly show that competition and feature-based attention modulate capture by the irrelevant onset to a large extent, whereas bottom-up color contrasts do not modulate onset capture. These results indicate the need to revise current accounts of gaze control.

Novelty and saliency in attentional capture by unannounced motion singletons

The present study examined attentional capture by an unannounced motion singleton in a visual search task. The results showed that a motion singleton only captured attention on its first unannounced occurrence when the observers had not encountered moving items before in the experiment, whereas it failed to capture when observers were familiar with moving items. This indicates that motion can capture attention independently of top-down attentional control settings, but only when motion as a feature is unexpected and new. An additional experiment tested whether salient items can capture attention when all stimuli possess new and unexpected features, and novelty information cannot guide attention. The results showed that attention was shifted to the location of the salient item when all items were new and unexpected, reinforcing the view that salient items receive attentional priority. The implications of these results for current theories of attention are discussed.