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.     

Visual routines for extracting magnitude relations

Linking relations described in text with relations in visualizations is often difficult. We used eye tracking to measure the optimal way to extract such relations in graphs, college students, and young children (6- and 8-year-olds). Participants compared relational statements (“Are there more blueberries than oranges?”) with simple graphs, and two systematic patterns emerged: eye movements that followed the verbal order of the question (inspecting the “blueberry” value first) versus those that followed a left-first bias (regardless of the left value’s identity). Question-order patterns led substantially to faster responses and increased in prevalence with age, whereas the left-first pattern led to far slower responses and was the dominant strategy for younger children. We argue that the optimal way to verify a verbally expressed relation’s consistency with visualization is for the eyes to mimic the verbal ordering but that this strategy requires executive control and coordination with language.     

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.     

Rapid eye-fixation training without eyetracking

Maintenance of stable central eye fixation is crucial for a variety of behavioral, electrophysiological, and neuroimaging experiments. Naive observers in these experiments are not typically accustomed to fixating, either requiring the use of cumbersome and costly eyetracking or producing confounds in results. We devised a flicker display that produced an easily detectable visual phenomenon whenever the eyes moved. A few minutes of training using this display dramatically improved the accuracy of eye fixation while observers performed a demanding spatial attention cuing task. The same amount of training using control displays did not produce significant fixation improvements, and some observers consistently made eye movements to the peripheral attention cue, contaminating the cuing effect. Our results indicate that (1) eye fixation can be rapidly improved in naive observers by providing real-time feedback about eye movements, and (2) our simple flicker technique provides an easy and effective method for providing this feedback. S. Suzuki, satoru@northwestern.edu     

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.     

Common-fate grouping as feature selection

The visual system groups elements within the visual field that are physically separated yet similar to each other. Although grouping processes have been intensely studied for a century, the mechanisms of grouping remain elusive. We propose that a primary mechanism for grouping by common fate is attentional selection of a direction of motion. A unique prediction follows from this account: that the visual system must be limited to forming only a single common-fate group at a time, and that attempts to find a particular common-fate group among other groups, or among nongroups, should therefore be highly inefficient. We show that this is true in searches for vertically oriented groups of moving dots among horizontally oriented groups (Experiment 1) and in searches for motion-linked groups among nonlinked objects (Experiment 2). Feature selection may limit the visual system to the construction of only one common-fate group at a time, and thus the experience of simultaneous grouping may be an illusion.     

Average orientation is more accessible through object boundaries than surface features

In a glance, the visual system can provide a summary of some kinds of information about objects in a scene. We explore how summary information about orientation is extracted and find that some representations of orientation are privileged over others. Participants judged the average orientation of either a set of 6 bars or 6 circular gratings. For bars, orientation information was carried by object boundary features, while for gratings, orientation was carried by internal surface features. The results showed more accurate averaging performance for bars than for gratings, even when controlling for potential differences in encoding precision for solitary objects. We suggest that, during orientation averaging, the visual system prioritizes object boundaries over surface features. This privilege for boundary features may lead to a better representation of the spatial layout of a scene.