The role of unique color changes and singletons in attention capture

Interference of Illusory Contour Perception by a Distractor

The visual system is capable of recognizing objects when object information is widely separated in space, as revealed by the Kanizsa-type illusory contours (ICs). Attentional involvement in perception of ICs is an important topic, and the present study examined whether and how the processing of ICs is interfered with by a distractor. Discrimination between thin and short deformations of an illusory circle was investigated in the absence or presence of a central dynamic patch, with difficulty of discrimination varied in three levels (easy, medium, and hard). Reaction time (RT) was significantly shorter in the absence compared to the presence of the distractor in the easy and medium conditions. Correct rate (CR) was significantly higher in the absence compared to the presence of the distractor in the easy condition, and the magnitude of the difference between CRs of distracted and non-distracted responses significantly reduced as task difficulty increased. These results suggested that perception of ICs is more likely to be vulnerable to distraction when more attentional resources remain available. The present finding supports that attention is engaged in perception of ICs and that distraction of IC processing is associated with perceptual load.

Stimulus-driven updating of long-term context memories in visual search

Visual search for a target is faster when the spatial layout of nontarget items is repeatedly encountered, illustrating that learned contextual invariances can improve attentional selection (contextual cueing). This type of contextual learning is usually relatively efficient, but relocating the target to an unexpected location (within otherwise unchanged layouts) typically abolishes contextual cueing. Here, we explored whether bottom-up attentional guidance can mediate the efficient contextual adaptation after the change. Two experiments presented an initial learning phase, followed by a subsequent relocation phase that introduced target location changes. This location change was accompanied by transient attention-guiding signals that either up-modulated the changed target location (Experiment 1), or which provided an inhibitory tag to down-modulate the initial target location (Experiment 2). The results from these two experiments showed reliable contextual cueing both before and after the target location change. By contrast, an additional control experiment (Experiment 3) that did not present any attention-guiding signals together with the changed target showed no reliable cueing in the relocation phase, thus replicating previous findings. This pattern of results suggests that attentional guidance (by transient stimulus-driven facilitatory and inhibitory signals) enhances the flexibility of long-term contextual learning.

Attentional dwelling and capture by color singletons

Can salient stimuli-such as color singletons and abrupt onsets-involuntarily capture spatial attention? We previously reported evidence that abrupt onsets can capture attention, but the effects of this capture can become latent under easy visual search. The present experiments examined whether a similar pattern of latent capture occurs for task-irrelevant color singletons. Participants searched for a perfect circle among oval distractors. We manipulated search difficulty by varying the width of the oval distractors, making them more or less target-like (i.e., more or less circular). With search displays of homogeneous distractors, cue validity effects increased linearly with search difficulty, indicating capture by color singletons (Experiments 1 and 2). With heterogeneous distractors, however, discouraging the use of singleton-detection mode to find the target circle, cue validity effects from color singletons were negligible at all difficulty levels (Experiment 3). Using these exact same heterogeneous search displays, meanwhile, abrupt onsets produced very large cue validity effects (Experiment 4). We conclude that whereas abrupt onsets can capture attention based purely on salience, static color singletons capture attention only when made task-relevant by promoting singleton-detection mode (i.e., contingent capture). The data further support an attentional dwelling account of capture costs and reinforce the recommendation that, to ensure sensitivity to detect the presence (or absence) of attention capture, capture experiments should employ a difficult visual search.

Predictive visual search: Role of environmental regularities in the learning of context cues

Repeatedly searching through invariant spatial arrangements in visual search displays leads to the buildup of memory about these displays (contextual-cueing effect). In the present study, we investigate (1) whether contextual cueing is influenced by global statistical properties of the task and, if so, (2) whether these properties increase the overall strength (asymptotic level) or the temporal development (speed) of learning. Experiment 1a served as baseline against which we tested the effects of increased or decreased proportions of repeated relative to nonrepeated displays (Experiments 1b and 1c, respectively), thus manipulating the global statistical properties of search environments. Importantly, probability variations were achieved by manipulating the number of nonrepeated (baseline) displays so as to equate the total number of repeated displays across experiments. In Experiment 1d, repeated and nonrepeated displays were presented in longer streaks of trials, thus establishing a stable environment of sequences of repeated displays. Our results showed that the buildup of contextual cueing was expedited in the statistically rich Experiments 1b and 1d, relative to the baseline Experiment 1a. Further, contextual cueing was entirely absent when repeated displays occurred in the minority of trials (Experiment 1c). Together, these findings suggest that contextual cueing is modulated by observers' assumptions about the reliability of search environments.

What pops out for you pops out for fish: Four common visual features

Visual search is the ability to detect a target of interest against a background of distracting objects. For many animals, performing this task fast and accurately is crucial for survival. Typically, visual-search performance is measured by the time it takes the observer to detect a target against a backdrop of distractors. The efficiency of a visual search depends fundamentally on the features of the target, the distractors, and the interaction between them. Substantial efforts have been devoted to investigating the influence of different visual features on visual-search performance in humans. In particular, it has been demonstrated that color, size, orientation, and motion are efficient visual features to guide attention in humans. However, little is known about which features are efficient and which are not in other vertebrates. Given earlier observations that moving targets elicit pop-out and parallel search in the archerfish during visual-search tasks, here we investigate and confirm that all four of these visual features also facilitate efficient search in the archerfish in a manner comparable to humans. In conjunction with results reported for other species, these finding suggest universality in the way visual search is carried out by animals despite very different brain anatomies and living environments.

The Effect of Ratio of Changing to Static Stimuli on the Attentional Capture

Studies have shown that appearing or disappearing objects attract more attention than static objects. This study examined the modulation of attention attracted by transient signals by systematically manipulating the ratio of changing (appearing/disappearing) to static stimuli. The results revealed that the effect of transient stimuli in attracting attention was diminished by simultaneously appearing (disappearing) peripheral stimuli and that the position where nothing was presented (the remaining stimulus) attracted attention when the number of appearing (disappearing) peripheral stimuli was increased. These findings suggest that the sudden change does not always capture attention, and whether changed things are attended or unchanged things are attended is determined depending on the proportion of things that change and do not change.

Change perception and change interference within and across feature dimensions

The ability to perceive a change in a visual object is reduced when that change is presented in competition with other changes which are task-irrelevant. We performed two experiments which investigate the basis of this change interference effect. We tested whether change interference occurs as a consequence of some form of attentional capture, or whether the interference occurs at a stage prior to attentional selection of the task-relevant change. A modified probe-detection task was used to explore this issue. Observers were required to report the presence/absence of a specified change-type (colour, shape) in the probe, in a context in which - on certain trials - irrelevant changes occur in non-probe items. There were two key variables in these experiments: the attentional state of the observer, and the dimensional congruence of changes in the probe and non-probe items. Change interference was strongest when the irrelevant changes were the same as those on the report dimension. However the interference pattern persisted even when observers did not know the report dimension at the time the changes occurred. These results seem to rule out attention as a factor. Our results fit best with an interpretation in which change interference produces feature-specific sensory noise which degrades the signal quality of the target change.

Out with the new, in with the old: Exogenous orienting to locations with physically constant stimulation

Dominant methods of investigating exogenous orienting presume that attention is captured most effectively at locations containing new events. This is evidenced by the ubiquitous use of transient stimuli as cues in the literature on exogenous orienting. In the present study, we showed that attention can be oriented exogenously toward a location containing a completely unchanging stimulus by modifying Posner's landmark exogenous spatial-cueing paradigm. Observers searched a six-element array of placeholder stimuli for an onset target. The target was preceded by a decrement in luminance to five of the six placeholders, such that one location remained physically constant. This "nonset" stimulus (so named to distinguish it from a traditional onsetting transient) acted as an exogenous cue, eliciting patterns of facilitation and inhibition at the nonset location and demonstrating that exogenous orienting is not always evident at the location of a visual transient. This method eliminates the decades-long confounding of orienting to a location with the processing of new events at that location, permitting alternative considerations of the nature of attentional selection.