Stimulus-driven attentional capture by subliminal onset cues

The effect of rear bicycle light configurations on drivers' perception of cyclists' presence and proximity

The optimal cycle light configuration for maximizing cyclists' conspicuity to drivers is not clear. Advances in sensor technology has led to the development of 'reactive' cycle lights that detect changes in the environment and consequently increase their flashing speed and brightness in risky situations - for example, when a rearward car is approaching - but no research has examined the effect of such lights on driver perception. The aim of the present study is to compare different cycle light configurations, including 'reactive' light technology, on drivers' ability to detect cyclists and estimate their proximity. We recruited 32 drivers to participate in two experiments, in which they viewed life-size real-world stimuli filmed from a driver's perspective in daytime and at dusk. The footage showed a cyclist on a bicycle with a rear light mounted on the seat post, in various configurations: static light, steady flashing, reactive flashing and no light. In Experiment 1, the drivers were required to detect the presence or absence of a cyclist on the road ahead as quickly as possible. In Experiment 2, they were required to estimate the distance of the cyclist from their vehicle, and to rate their confidence in their estimates. Experiment 1 revealed that drivers were quicker to detect the cyclist's presence in all rear cycle light conditions relative to the no light condition, but there were no differences in speed or accuracy across rear light conditions. Experiment 2 showed that drivers were more accurate in estimating the cyclist's proximity in the steady flashing and reactive flashing conditions, compared to static and no light conditions. Drivers were also more confident in their judgements in all rear light conditions compared to the no light condition. In conclusion, flashing rear cycle lights, regardless of reactive technology, enhanced drivers' perception of a cyclist ahead, notably in terms of their judgements of distance to that cyclist. Further investigation is needed to fully understand the impact of cycle light technology on driver perception, as well as the use of drivers' distance-to-cyclist estimates as an index of cyclists' cognitive conspicuity.

Mental imagery and visual attentional templates: A dissociation

There is a growing interest in the relationship between mental images and attentional templates as both are considered pictorial representations that involve similar neural mechanisms. Here, we investigated the role of mental imagery in the automatic implementation of attentional templates and their effect on involuntary attention. We developed a novel version of the contingent capture paradigm designed to encourage the generation of a new template on each trial and measure contingent spatial capture by a template-matching visual feature (color). Participants were required to search at four different locations for a specific object indicated at the start of each trial. Immediately prior to the search display, color cues were presented surrounding the potential target locations, one of which matched the target color (e.g., red for strawberry). Across three experiments, our task induced a robust contingent capture effect, reflected by faster responses when the target appeared in the location previously occupied by the target-matching cue. Contrary to our predictions, this effect remained consistent regardless of self-reported individual differences in visual mental imagery (Experiment 1, N = 216) or trial-by-trial variation of voluntary imagery vividness (Experiment 2, N = 121). Moreover, contingent capture was observed even among aphantasic participants, who report no imagery (Experiment 3, N = 91). The magnitude of the effect was not reduced in aphantasics compared to a control sample of non-aphantasics, although the two groups reported substantial differences in their search strategy and exhibited differences in overall speed and accuracy. Our results hence establish a dissociation between the generation and implementation of attentional templates for a visual feature (color) and subjectively experienced imagery.

Subliminal meaning-contingent attentional orienting: The role of attentional control setting based on displaywide features

People’s subjective factors can affect the spatial allocation of attention, and objects that are more in line with people’s expectations are easier to attract attention. In the current study, we wanted to know whether the meaning-contingent spatial attentional orienting could occur at the subliminal level, that is, whether conscious awareness was needed, and which attentional control settings worked. The current study employed a modified spatial cueing paradigm and the cues were made imperceptible by backward masking. The results showed that the capture effects of the left and the right positions stemmed from the meaning-contingent attentional control setting based on displaywide features, while the inhibition effect of the lower position and the capture effect of the upper position stemmed from the abrupt onset of subliminal cues and their masks. It is concluded that the attentional orienting of meaning contingency could occur at the subliminal level, which was not restricted by conscious perception. In particular, the attentional control setting based on displaywide features played an important role in spatial attentional orienting, which was manifested in the consistent capture effects on the horizontal sides. This study refined and separated the spatial attentional orienting effects, supported the contingent involuntary attentional orienting hypothesis, and expanded its scope of application.

Automatic capture of attention by flicker

Visual motion captures attention, but little is known about the automaticity of these effects. Here, we tested if deviant flicker frequencies, as one form of motion, automatically capture attention. Observers searched for a vertical target among tilted distractors. Prior to the target display, a cue array of sinusoidally modulating (flickering) annuli, each surrounding one location of the subsequent target(-plus-distractors) display was presented for variable durations. Annuli either flickered all at 1 Hz (neutral condition, no-singleton cue), or a single annulus flickered at a unique frequency of 5 Hz, 10 Hz, or 15 Hz. The location of this singleton-frequency cue was uncorrelated with target location. Thus, we could measure benefits (target at cued location) and costs (target ≠ cued location) for cues of different frequencies and durations. The results showed that deviant flicker frequencies capture attention, as we observed benefits and costs, falsifying that nonspatial filtering accounted for the cueing effect. In line with automatic capture, cueing was effective in singleton (Experiment 1) and nonsingleton search tasks (Experiment 2), and is thus not dependent on (“top-down”) singleton detection mode. Moreover, analysis of results ruled out trial-by-trial “swapping” of flicker frequencies from preceding target to subsequent distractor locations. Results also revealed increasing cueing effects with higher cue flicker frequency and longer duration. This indicates a significantly longer period of automatic capture by sinusoidal flicker than the typical inhibition of return observed around 250 ms after the onset of uninformative static or single-transient cues.

Awareness and Stimulus-Driven Spatial Attention as Independent Processes

To investigate the relation between attention and awareness, we manipulated visibility/awareness and stimulus-driven attention capture among metacontrast-masked visual stimuli. By varying the time interval between target and mask, we manipulated target visibility measured as target discrimination accuracies (ACCs; Experiments 1 and 2) and as subjective awareness ratings (Experiment 3). To modulate stimulus-driven attention capture, we presented the masked target either as a color-singleton (the target stands out by its unique color among homogeneously colored non-singletons), as a non-singleton together with a distractor singleton elsewhere (an irrelevant distractor has a unique color, whereas the target is colored like the other stimuli) or without a singleton (no stimulus stands out; only in Experiment 1). As color singletons capture attention in a stimulus-driven way, we expected target visibility/discrimination performance to be best for target singletons and worst with distractor singletons. In Experiments 1 and 2, we confirmed that the masking interval and the singleton manipulation influenced ACCs in an independent way and that attention capture by the singletons, with facilitated performance in target-singleton compared to distractor-singleton conditions, was found regardless of the interval-induced (in-)visibility of the targets. In Experiment 1, we also confirmed that attention capture was the same among participants with worse and better visibility/discrimination performance. In Experiment 2, we confirmed attention capture by color singletons with better discrimination performance for probes presented at singleton position, compared to other positions. Finally, in Experiment 3, we found that attention capture by target singletons also increased target awareness and that this capture effect on subjective awareness was independent of the effect of the masking interval, too. Together, results provide new evidence that stimulus-driven attention and awareness operate independently from one another and that stimulus-driven attention capture can precede awareness.

To look or not to look: Subliminal abruptonset cues influence constrained free-choice saccades

Subliminal cues have been shown to capture attention and modulate manual response behaviour but their impact on eye movement behaviour is not well-studied. In two experiments, we examined if subliminal cues influence constrained free-choice saccades and if this influence is under strategic control as a function of task-relevancy of the cues. On each trial, a display containing four filled circles at the centre of each quadrant was shown. A central coloured circle indicated the relevant visual field on each trial (Up or Down in Experiment 1; Left or Right in Experiment 2). Next, abrupt-onset cues were presented for 16 ms at one of the four locations. Participants were then asked to freely choose and make a saccade to one of the two target circles in the relevant visual field. The analysis of the frequency of saccades, saccade endpoint deviation and saccade latency revealed a significant influence of the relevant subliminal cues on saccadic decisions. Latency data showed reduced capture by spatiallyirrelevant cues under some conditions. These results indicate that spatial attentional control settings as defined in our study could modulate the influence of subliminal abrupt-onset cues on eye movement behaviour. We situate the findings of this study in the attention-capture debate and discuss the implications for the subliminal cueing literature.

The Nature of Unconscious Attention to Subliminal Cues

Attentional selection in humans is mostly determined by what is important to them or by the saliency of the objects around them. How our visual and attentional system manage these various sources of attentional capture is one of the most intensely debated issues in cognitive psychology. Along with the traditional dichotomy of goal-driven and stimulus-driven theories, newer frameworks such as reward learning and selection history have been proposed as well to understand how a stimulus captures attention. However, surprisingly little is known about the different forms of attentional control by information that is not consciously accessible to us. In this article, we will review several studies that have examined attentional capture by subliminal cues. We will specifically focus on spatial cuing studies that have shown through response times and eye movements that subliminal cues can affect attentional selection. A majority of these studies have argued that attentional capture by subliminal cues is entirely automatic and stimulus-driven. We will evaluate their claims of automaticity and contrast them with a few other studies that have suggested that orienting to unconscious cues proceeds in a manner that is contingent with the top-down goals of the individual. Resolving this debate has consequences for understanding the depths and the limits of unconscious processing. It has implications for general theories of attentional selection as well. In this review, we aim to provide the current status of research in this domain and point out open questions and future directions.

Perceptual learning induces active suppression of physically nonsalient shapes

Visual attention can be attracted by salient-but-irrelevant features, a phenomenon called attentional capture. Accompanying attentional capture, a top-down inhibitory mechanism is usually enacted to suppress the attentional shift. Our recent study showed that a physically nonsalient shape, which may be considered as a conjunction of basic features within the form domain, can also provoke a robust capture of attention as a consequence of perceptual learning, supporting an important role of prior experience in attentional deployment. It remains unclear, however, whether prior experience can also induce attentional suppression to conjunctions of features. Here, we examine whether and in which condition the brain would initiate an active suppression process to a physically nonsalient shape which has acquired an ability to capture attention after perceptual learning. We show that detectability of a shape after perceptual learning may be a key factor determining whether the shape would be actively suppressed or not. After extensive training as a target in visual search, a physically nonsalient shape could elicit an N2pc component when it was a distractor in a visual search task or a peripheral irrelevant stimulus in a central focused attention task, indicating a capture of attention induced by perceptual learning. Following the N2pc component, a Pd component would be elicited by the trained shape only if its detectability is relatively high. These findings suggest that an active suppression process could be applied not only to salient features but also to physically nonsalient shapes. A physically nonsalient shape could improve its salience through perceptual learning and would be actively suppressed when its learned salience reaches a certain level.

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.

The impact of temporal contingencies between cue and target onset on spatial attentional capture by subliminal onset cues

Prior research suggested that attentional capture by subliminal abrupt onset cues is stimulus driven. In these studies, reacting was faster when a searched-for target appeared at the location of a preceding abrupt onset cue compared to when the same target appeared at a location away from the cue (cueing effect), although the earlier onset of the cue was subliminal, because it appeared as one out of three horizontally aligned placeholders with a lead time that was too short to be noticed by the participants. Because the cueing effects seemed to be independent of top-down search settings for target features, the effect was attributed to stimulus-driven attentional capture. However, prior studies did not investigate if participants experienced the cues as useful temporal warning signals and, therefore, attended to the cues in a top-down way. Here, we tested to which extent search settings based on temporal contingencies between cue and target onset could be responsible for spatial cueing effects. Cueing effects were replicated, and we showed that removing temporal contingencies between cue and target onset did not diminish the cueing effects (Experiments 1 and 2). Neither presenting the cues in the majority of trials after target onset (Experiment 1) nor presenting cue and target unrelated to one another (Experiment 2) led to a significant reduction of the spatial cueing effects. Results thus support the hypothesis that the subliminal cues captured attention in a stimulus-driven way.

Dissociating the capture of attention from saccade activation by subliminal abrupt onsets

Attentional capture and effects on saccade metrics by subliminal abrupt onset cues have been studied with peripheral cues at one out of several (two to four) display locations, swiftly followed by additional onsets at the other display locations. The lead time of the cue was too short to be seen. Here, we were interested in whether such subliminal onset cues influenced saccades primarily by way of attention or by way of direct saccade activation. In separate blocks, participants made speeded pro-saccades towards a black target or anti-saccades away from the target. Prior to the targets, an abrupt onset cue was presented either at the same side as the target (valid condition) or at the opposite side (invalid condition). If cues influenced performance by way of attentional capture, we expected facilitation of target processing in valid compared to invalid conditions (cueing effect) in the pro- as well as in the anti-saccade task. If the cues activated saccades in their direction, we expected the cueing effect to drop in the anti-saccade task compared to the pro-saccade task because in the anti-saccade task the invalid cue would activate the finally required response, whereas the valid cue would activate the alternative response, leading to interference. Results were in line with the former of these possibilities suggesting that subliminal abrupt onsets influenced saccades by way of attention with no or little direct activation of saccades.

Neural processes underlying the orienting of attention without awareness

Despite long being of interest to both philosophers and scientists, the relationship between attention and perceptual awareness is not well understood, especially to what extent they are even dissociable. Previous studies have shown that stimuli of which we are unaware can orient spatial attention and affect behavior. Yet, relatively little is understood about the neural processes underlying such unconscious orienting of attention, and how they compare to conscious orienting. To directly compare the cascade of attentional processes with and without awareness of the orienting stimulus, we employed a spatial-cueing paradigm and used object-substitution masking to manipulate subjects' awareness of the cues. We recorded EEG during the task, from which we extracted hallmark event-related-potential (ERP) indices of attention. Behaviorally, there was a 61 ms validity effect (invalidly minus validly cued target RTs) on cue-aware trials. On cue-unaware trials, subjects also had a robust validity effect of 20 ms, despite being unaware of the cue. An N2pc to the cue, a hallmark ERP index of the lateralized orienting of attention, was observed for cue-aware but not cue-unaware trials, despite the latter showing a clear behavioral validity effect. Finally, the P1 sensory-ERP response to the targets was larger when validly versus invalidly cued, even when subjects were unaware of the preceding cue, demonstrating enhanced sensory processing of targets following subliminal cues. These results suggest that subliminal stimuli can orient attention and lead to subsequent enhancements to both stimulus sensory processing and behavior, but through different neural mechanisms (such as via a subcortical pathway) than stimuli we perceive.

Bridging views in cinema: a review of the art and science of view integration

Recently, there has been a surge of interest in the relationship between film and cognitive science. This is reflected in a new science of cinema that can help us both to understand this art form, and to produce new insights about cognition and perception. In this review, we begin by describing how the initial development of cinema involved close observation of audience response. This allowed filmmakers to develop an informal theory of visual cognition that helped them to isolate and creatively recombine fundamental elements of visual experience. We review research exploring naturalistic forms of visual perception and cognition that have opened the door to a productive convergence between the dynamic visual art of cinema and science of visual cognition that can enrich both. In particular, we discuss how parallel understandings of view integration in cinema and in cognitive science have been converging to support a new understanding of meaningful visual experience. WIREs Cogn Sci 2017, 8:e1436. doi: 10.1002/wcs.1436 For further resources related to this article, please visit the WIREs website.

Subliminal or not? Comparing null-hypothesis and Bayesian methods for testing subliminal priming

A difficulty for reports of subliminal priming is demonstrating that participants who actually perceived the prime are not driving the priming effects. There are two conventional methods for testing this. One is to test whether a direct measure of stimulus perception is not significantly above chance on a group level. The other is to use regression to test if an indirect measure of stimulus processing is significantly above zero when the direct measure is at chance. Here we simulated samples in which we assumed that only participants who perceived the primes were primed by it. Conventional analyses applied to these samples had a very large error rate of falsely supporting subliminal priming. Calculating a Bayes factor for the samples very seldom falsely supported subliminal priming. We conclude that conventional tests are not reliable diagnostics of subliminal priming. Instead, we recommend that experimenters calculate a Bayes factor when investigating subliminal priming.

Reversed Priming Effects May Be Driven by Misperception Rather than Subliminal Processing

A new paradigm for investigating whether a cognitive process is independent of perception was recently suggested. In the paradigm, primes are shown at an intermediate signal strength that leads to trial-to-trial and inter-individual variability in prime perception. Here, I used this paradigm and an objective measure of perception to assess the influence of prime identification responses on Stroop priming. I found that sensory states producing correct and incorrect prime identification responses were also associated with qualitatively different priming effects. Incorrect prime identification responses were associated with reversed priming effects but in contrast to previous studies, I interpret this to result from the (mis-)perception of primes rather than from a subliminal process. Furthermore, the intermediate signal strength also produced inter-individual variability in prime perception that strongly influenced priming effects: only participants who on average perceived the primes were Stroop primed. I discuss how this new paradigm, with a wide range of d′ values, is more appropriate when regression analysis on inter-individual identification performance is used to investigate perception-dependent processing. The results of this study, in line with previous results, suggest that drawing conclusions about subliminal processes based on data averaged over individuals may be unwarranted.

S-ketamine influences strategic allocation of attention but not exogenous capture of attention

We investigated whether s-ketamine differentially affects strategic allocation of attention. In Experiment 1, (1) a less visible cue was weakly masked by the onsets of competing placeholders or (2) a better visible cue was not masked because it was presented in isolation. Both types of cue appeared more often opposite of the target (75%) than at target position (25%). With this setup, we tested for strategic attention shifts to the opposite side of the cues and for exogenous attentional capture toward the cue's side in a short cue-target interval, as well as for (reverse) cueing effects in a long cue-target interval after s-ketamine and after placebo treatment in a double-blind within-participant design. We found reduced strategic attention shifts after cues presented without placeholders for the s-ketamine compared to the placebo treatment in the short interval, indicating an early effect on the strategic allocation of attention. No differences between the two treatments were found for exogenous attentional capture by less visible cues, suggesting that s-ketamine does not affect exogenous attentional capture in the presence of competing distractors. Experiment 2 confirmed that the competing onsets of the placeholders prevented the strategic cueing effect. Taken together, the results indicate that s-ketamine affects strategic attentional capture, but not exogenous attentional capture. The findings point to a more prominent role of s-ketamine during top-down controlled forms of attention that require suppression of automatic capture than during automatic capture itself.