Can a single short-term mechanism account for priming of pop-out?

Priming of probabilistic attentional templates

Attentional priming has a dominating influence on vision, speeding visual search, releasing items from crowding, reducing masking effects, and during free-choice, primed targets are chosen over unprimed ones. Many accounts postulate that templates stored in working memory control what we attend to and mediate the priming. But what is the nature of these templates (or representations)? Analyses of real-world visual scenes suggest that tuning templates to exact color or luminance values would be impractical since those can vary greatly because of changes in environmental circumstances and perceptual interpretation. Tuning templates to a range of the most probable values would be more efficient. Recent evidence does indeed suggest that the visual system represents such probability, gradually encoding statistical variation in the environment through repeated exposure to input statistics. This is consistent with evidence from neurophysiology and theoretical neuroscience as well as computational evidence of probabilistic representations in visual perception. I argue that such probabilistic representations are the unit of attentional priming and that priming of, say, a repeated single-color value simply involves priming of a distribution with no variance. This "priming of probability" view can be modelled within a Bayesian framework where priming provides contextual priors. Priming can therefore be thought of as learning of the underlying probability density function of the target or distractor sets in a given continuous task.

Top-down imagery overrides the influence of selection history effects

The present study investigated whether color imagery could override the representations of the prevalent selection history effect termed Priming of Pop-out (PoP), which is constituted by faster responding when the target color is repeated rather than switched across trials of color singleton search. Participants imagined a color in the interval between trials of a color singleton search task that could be the same as or different to the previous target color, and they were to rate the vividness of these representations following each imagery event. It was revealed that when highly vivid imagery was reported, the PoP effect was attenuated relative to less vivid forms of it (and absent in two out of three experiments), and that color imagery eliminated the build-up of priming following consecutive target color repeats. Overall, the present findings suggest the representations of the selection history system can be overridden by top-down imagery.

Getting it right from the start: Attentional control settings without a history of target selection

Observers can adopt attentional control settings that regulate how their attention is drawn to salient stimuli in the environment. Do observers choose their attentional control settings voluntarily, or are they primed in a bottom-up manner based on the stimuli that the observer has recently attended and responded to (i.e., target-selection history)? In the present experiment, we tested these two accounts using a long-term memory attentional control settings paradigm, in which participants memorized images of 18 common visual objects, and then searched for those objects in a spatial blink task. Unbeknownst to participants, we manipulated priming by dividing the set of target objects into two subsets: nine objects appeared frequently as targets in the spatial blink task (frequently primed objects), and nine infrequently (infrequently primed objects). We assessed attentional capture by presenting these objects as distractors in the spatial blink task and measuring their effect on task accuracy. We found that both subsets of objects captured attention more than non-studied objects, and frequently primed objects did not capture attention more than infrequently primed objects. Moreover, a follow-up analysis revealed that all studied objects captured attention, even before those objects had appeared as targets in the spatial blink task. These findings suggest that priming through target-selection history plays little-to-no role in long-term memory attentional control settings. Rather, these findings align with a growing body of evidence that attentional control settings are primarily implemented through voluntary control.

Testing a priming account of the contingent-capture effect

In the contingent-capture protocol, singleton cues that have a target's searched-for feature capture attention, but cues that do not have the target's searched-for feature do not, a result labeled the contingent-capture effect. The contingent-capture effect is usually regarded as evidence for the observers' ability to establish search settings for certain nonspatial features in a top-down manner. However, in recent years it has become increasingly clear that selection history is also a powerful mediator of attentional capture. In this vein, it has been suggested that contingent-capture effects could emerge as a result of (intertrial) priming: The idea is that features that have been encountered previously in the target are primed, so that cues that have these features automatically capture attention in a subsequent encounter. Here we tested a strong version of the priming account of the contingent-capture effect. We wanted to know whether cues that had target features would capture attention when the corresponding features were not part of the instructions (i.e., when the corresponding features were task-irrelevant). The results suggested that a strong version of the priming account of contingent capture is not supported. In five experiments, we found little evidence that the contingent-capture effect could be explained by (intertrial) priming of task-irrelevant features alone. These results show that processes beyond priming through task-irrelevant features are critical for contingent-capture effects.

A meta-analysis of contingent-capture effects

The present meta-analyses investigated the widely used contingent-capture protocol. Contingent-capture theory postulates that only top-down matching stimuli capture attention. Evidence comes from the contingent-capture protocol, in which participants search for a predefined target stimulus preceded by a spatial cue. The cue is typically uninformative of the target's position but either presented at target position (valid condition) or away from the target (invalid condition). The common finding is that seemingly only top-down matching cues capture attention as shown by a selective cueing effect (faster responses in valid than invalid conditions) for cues with a feature similar to the searched-for target only, but not for cues without target-similar feature. The origin of this "contingent-capture effect" is, however, debated. One alternative explanation is that intertrial priming-the priming of attention capture by the cue in a given trial by attending to a feature-similar target in the preceding trial-mediates the contingent-capture effect. Alternatively, the rapid-disengagement account argues that all salient stimuli capture attention initially, but that the disengagement from non-matching cues is rapid. The present meta-analyses shed light on this debate by (a) identifying moderators of the size of reported contingent-capture effects (64 experiments) and (b) analyzing pure (blocked) versus mixed presentation of different targets as well as summarizing results of published intertrial priming studies (12 experiments) in the contingent-capture protocol. We found target-singleton versus non-singleton status and pure versus mixed presentation of different targets to be reliable moderators. Furthermore, results indicated the presence of publication bias. Otherwise, the contingent-capture theory was supported, but we discuss additional factors that must be taken into account for a full account of the results.

Inter-trial effects in visual pop-out search: Factorial comparison of Bayesian updating models

Many previous studies on visual search have reported inter-trial effects, that is, observers respond faster when some target property, such as a defining feature or dimension, or the response associated with the target repeats versus changes across consecutive trial episodes. However, what processes drive these inter-trial effects is still controversial. Here, we investigated this question using a combination of Bayesian modeling of belief updating and evidence accumulation modeling in perceptual decision-making. In three visual singleton ('pop-out') search experiments, we explored how the probability of the response-critical states of the search display (e.g., target presence/absence) and the repetition/switch of the target-defining dimension (color/ orientation) affect reaction time distributions. The results replicated the mean reaction time (RT) inter-trial and dimension repetition/switch effects that have been reported in previous studies. Going beyond this, to uncover the underlying mechanisms, we used the Drift-Diffusion Model (DDM) and the Linear Approach to Threshold with Ergodic Rate (LATER) model to explain the RT distributions in terms of decision bias (starting point) and information processing speed (evidence accumulation rate). We further investigated how these different aspects of the decision-making process are affected by different properties of stimulus history, giving rise to dissociable inter-trial effects. We approached this question by (i) combining each perceptual decision making model (DDM or LATER) with different updating models, each specifying a plausible rule for updating of either the starting point or the rate, based on stimulus history, and (ii) comparing every possible combination of trial-wise updating mechanism and perceptual decision model in a factorial model comparison. Consistently across experiments, we found that the (recent) history of the response-critical property influences the initial decision bias, while repetition/switch of the target-defining dimension affects the accumulation rate, likely reflecting an implicit 'top-down' modulation process. This provides strong evidence of a disassociation between response- and dimension-based inter-trial effects.

The effect of encoding duration on implicit and explicit eyewitness memory

The present study investigated the effect of encoding duration on implicit and explicit eyewitness memory. Participants (N = 227) viewed a mock crime (brief, 15-s vs. long, 30-s vs. irrelevant/control) and were then tested with both implicit and explicit memory prompts or with explicit memory prompts only. Brief-encoding participants revealed more critical details implicitly than long-encoding or control participants. Further, the number and percentage of accurate details recalled explicitly were higher for long-encoding than for brief-encoding participants. Implicit testing prior to explicit recall-as compared to completing a filler task-was detrimental to free recall performance. Interestingly, brief-encoding participants were significantly more likely to remember critical details implicitly but not explicitly than long-encoding participants. This is the first study to investigate implicit eyewitness memory for a multimodal mock crime. Findings are theoretically consistent with prior research on cognition while expanding upon the extant eyewitness memory and investigative interviewing literature.

How functional are functional viewing fields?

Hulleman & Olivers' (H&O's) proposal is a refreshing addition to the visual search literature. Although we like their proposal that fixations, not individual items should be considered a fundamental unit in visual search, we point out some unresolved problems that their account will have to solve. Additionally, we consider predictions that can be made from the account, in particular in relation to priming of visual search, finding that the account generates interesting testable predictions.

You prime what you code: The fAIM model of priming of pop-out

Our visual brain makes use of recent experience to interact with the visual world, and efficiently select relevant information. This is exemplified by speeded search when target- and distractor features repeat across trials versus when they switch, a phenomenon referred to as intertrial priming. Here, we present fAIM, a computational model that demonstrates how priming can be explained by a simple feature-weighting mechanism integrated into an established model of bottom-up vision. In fAIM, such modulations in feature gains are widespread and not just restricted to one or a few features. Consequentially, priming effects result from the overall tuning of visual features to the task at hand. Such tuning allows the model to reproduce priming for different types of stimuli, including for typical stimulus dimensions such as 'color' and for less obvious dimensions such as 'spikiness' of shapes. Moreover, the model explains some puzzling findings from the literature: it shows how priming can be found for target-distractor stimulus relations rather than for their absolute stimulus values per se, without an explicit representation of relations. Similarly, it simulates effects that have been taken to reflect a modulation of priming by an observers' goals-without any representation of goals in the model. We conclude that priming is best considered as a consequence of a general adaptation of the brain to visual input, and not as a peculiarity of visual search.

How visual working memory contents influence priming of visual attention

Recent evidence shows that when the contents of visual working memory overlap with targets and distractors in a pop-out search task, intertrial priming is inhibited (Kristjánsson, Sævarsson & Driver, Psychon Bull Rev 20(3):514-521, 2013, Experiment 2, Psychonomic Bulletin and Review). This may reflect an interesting interaction between implicit short-term memory-thought to underlie intertrial priming-and explicit visual working memory. Evidence from a non-pop-out search task suggests that it may specifically be holding distractors in visual working memory that disrupts intertrial priming (Cunningham & Egeth, Psychol Sci 27(4):476-485, 2016, Experiment 2, Psychological Science). We examined whether the inhibition of priming depends on whether feature values in visual working memory overlap with targets or distractors in the pop-out search, and we found that the inhibition of priming resulted from holding distractors in visual working memory. These results are consistent with separate mechanisms of target and distractor effects in intertrial priming, and support the notion that the impact of implicit short-term memory and explicit visual working memory can interact when each provides conflicting attentional signals.

Implicit short- and long-term memory direct our gaze in visual search

Visual attention is strongly affected by the past: both by recent experience and by long-term regularities in the environment that are encoded in and retrieved from memory. In visual search, intertrial repetition of targets causes speeded response times (short-term priming). Similarly, targets that are presented more often than others may facilitate search, even long after it is no longer present (long-term priming). In this study, we investigate whether such short-term priming and long-term priming depend on dissociable mechanisms. By recording eye movements while participants searched for one of two conjunction targets, we explored at what stages of visual search different forms of priming manifest. We found both long- and short- term priming effects. Long-term priming persisted long after the bias was present, and was again found even in participants who were unaware of a color bias. Short- and long-term priming affected the same stage of the task; both biased eye movements towards targets with the primed color, already starting with the first eye movement. Neither form of priming affected the response phase of a trial, but response repetition did. The results strongly suggest that both long- and short-term memory can implicitly modulate feedforward visual processing.