Feature-based attention resolves depth ambiguity.

Perceiving the world around us requires that we resolve ambiguity. This process is often studied in the lab using ambiguous figures whose structures can be interpreted in multiple ways. One class of figures contains ambiguity in its depth relations, such that either of two surfaces could be seen as being the "front" of an object. Previous research suggests that selectively attending to a given location on such objects can bias the perception of that region as the front. This study asks whether selectively attending to a distributed feature can also bias that region toward the front. Participants viewed a structure-from-motion display of a rotating cylinder that could be perceived as rotating clockwise or counterclockwise (as imagined viewing from the top), depending on whether a set of red or green moving dots were seen as being in the front. A secondary task encouraged observers to globally attend to either red or green. Results from both Experiment 1 and 2 showed that the dots on the cylinder that shared the attended feature, and its corresponding surface, were more likely to be seen as being in the front, as measured by participants' clockwise versus counterclockwise percept reports. Feature-based attention, like location-based attention, is capable of biasing competition among potential interpretations of figures with ambiguous structure in depth.

Eye movements during emotion recognition in faces.

When distinguishing whether a face displays a certain emotion, some regions of the face may contain more useful information than others. Here we ask whether people differentially attend to distinct regions of a face when judging different emotions. Experiment 1 measured eye movements while participants discriminated between emotional (joy, anger, fear, sadness, shame, and disgust) and neutral facial expressions. Participant eye movements primarily fell in five distinct regions (eyes, upper nose, lower nose, upper lip, nasion). Distinct fixation patterns emerged for each emotion, such as a focus on the lips for joyful faces and a focus on the eyes for sad faces. These patterns were strongest for emotional faces but were still present when viewers sought evidence of emotion within neutral faces, indicating a goal-driven influence on eye-gaze patterns. Experiment 2 verified that these fixation patterns tended to reflect attention to the most diagnostic regions of the face for each emotion. Eye movements appear to follow both stimulus-driven and goal-driven perceptual strategies when decoding emotional information from a face.

Enumeration of small collections violates Weber's law.

In a phenomenon called subitizing, we can immediately generate exact counts of small collections (one to three objects), in contrast to larger collections, for which we must either create rough estimates or serially count. A parsimonious explanation for this advantage for small collections is that noisy representations of small collections are more tolerable, due to the larger relative differences between consecutive numbers (e.g., 2 vs. 3 is a 50 % increase, but 10 vs. 11 is only a 10 % increase). In contrast, the advantage could stem from the fact that small-collection enumeration is more precise, relying on a unique mechanism. Here, we present two experiments that conclusively showed that the enumeration of small collections is indeed "superprecise." Participants compared numerosity within either small or large visual collections in conditions in which the relative differences were controlled (e.g., performance for 2 vs. 3 was compared with performance for 20 vs. 30). Small-number comparison was still faster and more accurate, across both "more-fewer" judgments (Exp. 1), and "same-different" judgments (Exp. 2). We then reviewed the remaining potential mechanisms that might underlie this superprecision for small collections, including the greater diagnostic value of visual features that correlate with number and a limited capacity for visually individuating objects.

Asymmetric coding of categorical spatial relations in both language and vision.

Describing certain types of spatial relationships between a pair of objects requires that the objects are assigned different "roles" in the relation, e.g., "A is above B" is different than "B is above A." This asymmetric representation places one object in the "target" or "figure" role and the other in the "reference" or "ground" role. Here we provide evidence that this asymmetry may be present not just in spatial language, but also in perceptual representations. More specifically, we describe a model of visual spatial relationship judgment where the designation of the target object within such a spatial relationship is guided by the location of the "spotlight" of attention. To demonstrate the existence of this perceptual asymmetry, we cued attention to one object within a pair by briefly previewing it, and showed that participants were faster to verify the depicted relation when that object was the linguistic target. Experiment 1 demonstrated this effect for left-right relations, and Experiment 2 for above-below relations. These results join several other types of demonstrations in suggesting that perceptual representations of some spatial relations may be asymmetrically coded, and further suggest that the location of selective attention may serve as the mechanism that guides this asymmetry.

Tracking multiple objects is limited only by object spacing, not by speed, time, or capacity.

In dealing with a dynamic world, people have the ability to maintain selective attention on a subset of moving objects in the environment. Performance in such multiple-object tracking is limited by three primary factors-the number of objects that one can track, the speed at which one can track them, and how close together they can be. We argue that this last limit, of object spacing, is the root cause of all performance constraints in multiple-object tracking. In two experiments, we found that as long as the distribution of object spacing is held constant, tracking performance is unaffected by large changes in object speed and tracking time. These results suggest that barring object-spacing constraints, people could reliably track an unlimited number of objects as fast as they could track a single object.

Objects with reduced visibility still contribute to size averaging.

People can rapidly judge the average size of a collection of objects with considerable accuracy. In this study, we tested whether this size-averaging process relies on relatively early object representations or on later object representations that have undergone iterative processing. We asked participants to judge the average size of a set of circles and, in some conditions, presented two additional circles that were either smaller or larger than the average. The additional circles were surrounded by four-dot masks that either lingered longer than the circle array, preventing further processing with object substitution masking (OSM), or disappeared simultaneously with the circle array, allowing the circle representation to reach later visual processing stages. Surprisingly, estimation of average circle size was modulated by both visible circles and circles whose visibility was impaired by OSM. There was also no correlation across participants between the influence of the masked circles and susceptibility to OSM. These findings suggest that relatively early representations of objects can contribute to the size-averaging process despite their reduced visibility.

Number estimation relies on a set of segmented objects.

How do we estimate the number of objects in a set? Two types of visual representations might underlie this ability - an unsegmented visual image or a segmented collection of discrete objects. We manipulated whether individual objects were isolated from each other or grouped into pairs by irrelevant lines. If number estimation operates over an unsegmented image, then this manipulation should not affect estimates. But if number estimation relies on a segmented image, then grouping pairs of objects into single units should lead to lower estimates. In Experiment 1 participants underestimated the number of grouped objects, relative to disconnected objects in which the connecting lines were 'broken'. Experiment 2 presents evidence that this segmentation process occurred broadly across the entire set of objects. In Experiment 3, a staircase procedure provides a quantitative measure of the underestimation effect. Experiment 4 shows that the strength of the grouping effect was equally strong for a single thin line, and the effect can be eliminated by a small break in the line. These results provide direct evidence that number estimation relies on a segmented input.

Evidence against a speed limit in multiple-object tracking.

Everyday tasks often require us to keep track of multiple objects in dynamic scenes. Past studies show that tracking becomes more difficult as objects move faster. In the present study, we show that this trade-off may not be due to increased speed itself but may, instead, be due to the increased crowding that usually accompanies increases in speed. Here, we isolate changes in speed from variations in crowding, by projecting a tracking display either onto a small area at the center of a hemispheric projection dome or onto the entire dome. Use of the larger display increased retinal image size and object speed by a factor of 4 but did not increase interobject crowding. Results showed that tracking accuracy was equally good in the large-display condition, even when the objects traveled far into the visual periphery. Accuracy was also not reduced when we tested object speeds that limited performance in the small-display condition. These results, along with a reinterpretation of past studies, suggest that we might be able to track multiple moving objects as fast as we can a single moving object, once the effect of object crowding is eliminated.

Change blindness in the absence of a visual disruption.

Findings from studies of visual memory and change detection have revealed a surprising inability to detect large changes to scenes from one view to the next ('change blindness'). When some form of disruption is introduced between an original and modified display, observers often fail to notice the change. This disruption can take many forms (e.g. an eye movement, a flashed blank screen, a blink, a cut in a motion picture, etc) with similar results. In all cases, the changes are sufficiently large that, were they to occur instantaneously, they would consistently be detected. Prior research on change blindness was predicated on the assumption that, in the absence of a visual disruption, the signal caused by the change would draw attention, leading to detection. In two experiments, we demonstrate that change blindness can occur even in the absence of a visual disruption. In one experiment, subjects actually detected more changes with a disruption than without one. When changes are sufficiently gradual, the visible change signal does not seem to draw attention, and large changes can go undetected. The findings are discussed in the context of metacognitive beliefs about change detection and the strategic decisions those beliefs entail.