Adriane E. Seiffert

Position displacement, not velocity, is the cue to motion detection of second-order stimuli.

Motion detection can be achieved either with mechanisms sensitive to a targets velocity, or sensitive to change in a targets position. Using a procedure to dissociate these two provided by Nakayama and Tyler (Vis Res 1981;21:427-433), we explored detection of first-order (luminance-based) and various second-order (texture-based and stereo-based) motion. In the first experiment, observers viewed annular gratings oscillating in rotational motion at various rates. For each oscillation temporal frequency, we determined the minimum displacement of the pattern for which observers could reliably see motion. For first-order motion, these motion detection thresholds decreased with increasing temporal frequency, and thus were determined by a minimum velocity. In contrast, motion detection thresholds for second-order motion remained roughly constant across temporal frequency, and thus were determined by a minimum displacement. In Experiment 2, luminance-based gratings of different contrasts were tested to show that the velocity-dependence was not an artifact of pattern visibility. In the remaining experiments, results similar to Experiment 1 were obtained with a central presentation of a linear grating, instead of an annular grating (Experiment 3), and with a motion discrimination (phase discrimination) rather than motion detection task (Experiment 4). We conclude that, within the ranges tested here, second-order motion is more readily detected with a mechanism which tracks the change of position of features over time.

Eye movements during multiple object tracking: Where do participants look?

Similar to the eye movements you might make when viewing a sports game, this experiment investigated where participants tend to look while keeping track of multiple objects. While eye movements were recorded, participants tracked either 1 or 3 of 8 red dots that moved randomly within a square box on a black background. Results indicated that participants fixated closer to targets more often than to distractors. However, on 3-target trials, fixation was closer to the center of the triangle formed by the targets more often than to any individual targets. This center-looking strategy seemed to reflect that people were grouping the targets into a single object rather than simultaneously minimizing all target eccentricities. Here we find that observers deliberately focus their eyes on a location that is different from the objects they are attending, perhaps as a consequence of representing those objects as a group.

Attentional Costs in Multiple-Object Tracking.

Attentional demands of multiple-object tracking were demonstrated using a dual-task paradigm. Participants were asked to make speeded responses based on the pitch of a tone, while at the same time tracking four of eight identical dots. Tracking difficulty was manipulated either concurrent with or after the tone task. If increasing tracking difficulty increases attentional demands, its effect should be larger when it occurs concurrent with the tone. In Experiment 1, tracking difficulty was manipulated by having all dots briefly attract one another on some trials, causing a transient increase in dot proximity and speed. Results showed that increasing proximity and speed had a significantly larger effect when it occurred at the same time as the tone task. Experiments 2 and 3 showed that manipulating either proximity or speed independently was sufficient to produce this pattern of results. Experiment 4 manipulated object contrast, which affected tracking performance equally whether it occurred concurrent with or after the tone task. Overall, results support the view that the moment-to-moment tracking of multiple objects demands attention. Understanding what factors increase the attentional demands of tracking may help to explain why tracking is sometimes successful and at other times fails.

Conflicting motion information impairs multiple object tracking

People can keep track of target objects as they move among identical distractors using only spatiotemporal information. We investigated whether or not participants use motion information during the moment-to-moment tracking of objects by adding motion to the texture of moving objects. The texture either remained static or moved relative to the objects direction of motion, either in the same direction, the opposite direction, or orthogonal to each objects trajectory. Results showed that, compared to the static texture condition, tracking performance was worse when the texture moved in the opposite direction of the object and better when the texture moved in the same direction as the object. Our results support the conclusion that motion information is used during the moment-to-moment tracking of objects. Motion information may either affect a representation of position or be used to periodically predict the future location of targets.

Inefficient visual search for second-order motion

Visual search rate was used to assess attentional resources required for detection of opposing motions defined either by luminance or by modulations of texture contrast, flicker, or size. Though luminance-based targets were detected quickly, search through second-order motion was slow. Control experiments ruled out stimuli visibility, complexity, eccentricity sensitivity, and attributes of the carrier as possible accounts. Results suggest separate processing of the two types of stimuli: Luminance-based motion is detected by spatiotemporal filters, whereas second-order motion is likely processed by a capacity-limited, later stage. Rate-reducing effects of increased contrast and speed mirrored previous research suggesting that effortful feature tracking may be the mechanism.

Tracking planets and moons: mechanisms of object tracking revealed with a new paradigm

People can attend to and track multiple moving objects over time. Cognitive theories of this ability emphasize location information and differ on the importance of motion information. Results from several experiments have shown that increasing object speed impairs performance, although speed was confounded with other properties such as proximity of objects to one another. Here, we introduce a new paradigm to study multiple object tracking in which object speed and object proximity were manipulated independently. Like the motion of a planet and moon, each target–distractor pair rotated about both a common local point as well as the center of the screen. Tracking performance was strongly affected by object speed even when proximity was controlled. Additional results suggest that two different mechanisms are used in object tracking—one sensitive to speed and proximity and the other sensitive to the number of distractors. These observations support models of object tracking that include information about object motion and reject models that use location alone.

Taking credit for success: The phenomenology of control in a goal-directed task

We studied how people determine when they are in control of objects. In a computer task, participants moved a virtual boat towards a goal using a joystick to investigate how subjective control is shaped by (1) correspondence between motor actions and the visual consequences of those actions, and (2) attainment of higher-level goals. In Experiment 1, random discrepancies from joystick input (noise) decreased judgments of control (JoCs), but discrepancies that brought the boat closer to the goal and increased success (the autopilot) increased JoCs. In Experiment 2, participants raced to the goal against a computer-controlled rival boat while varying levels of noise interfered with each boat. Participants reached the goal more often and rated their own control higher when the computer rival had good control. Subjective control over moving objects depends partly on consistency between motor actions and their effects, but is also modulated by perceived success and competition.

Updating Objects in Visual Short-Term Memory Is Feature Selective

The purpose of this study was to examine whether the process of updating information in visual short-term memory (VSTM) is object based. We investigated whether modifying the memory of one feature of an object would automatically promote refreshing the memory of all of its other features. The results showed that the facilitative effect of updating was specific to the updated feature of an object and did not spread to its nonupdated features. This feature-selective effect suggests that updating VSTM is not object based (Experiment 1), even though storage was object based (Experiment 2). Control experiments ruled out strategy-based (Experiment 3) and stimulus-related (Experiments 4–6) accounts. Feature-selective updating may indicate that the mechanism used to modify the contents of memory may have a different basis than that used to encode or store information in memory.

Biologically-Inspired Human-Swarm Interaction Metrics

Human-swarm interaction is an emerging field encompassing questions related to biology, robotics, computer science, human-computer interaction, and psychology. Swarms are large groups of individual entities that enact group behaviors; biological examples include fish, birds and insects. Swarms overwhelm humans’ abilities to monitor and interact with each entity. Human-robot and human-computer interaction metrics are inappropriate to describe human-swarm interactions alone due to the interaction challenges posed by swarms. It is unknown precisely how humans respond to interacting with swarms. The theory is that biological swarm metrics may be appropriate for analyzing human-swarm interaction. Nine human-swarm interaction metric categories derived from the biological and robotic swarm literature are presented, including example metrics from each category. This paper opens the discussion regarding what types of existing swarm metrics may be applicable and what categories of metrics will be important for human-swarm interaction assessment.

Motion aftereffects specific to surface depth order: beyond binocular disparity.

Despite evidence for concurrent processing of motion and stereopsis from psychophysics and neurophysiology, the detailed relationship between depth and motion processing is not yet clear. Using the contingent aftereffect paradigm, we investigated how the order of surfaces presented across depth influenced motion perception. After having observers adapt to two superimposed populations of dots moving in opposite directions at different binocular disparities, we assessed how much of the motion aftereffect (MAE) was specific to absolute disparity and how much was specific to the depth order of the surfaces. The test contained two planes of moving dots at several different pairs of disparities and asked observers to report the MAE direction at one of the planes (the target). In addition to the disparity-contingent MAE (Verstraten, Verlinde, Fredericksen, & van de Grind, 1994), we found MAEs dependent on surface order. When the target surface was in front of another surface, observers more often reported the MAE in the direction opposite to the front adapting surface than the back. This effect was observed despite differences in absolute and relative disparity between the adapted and test surfaces. The results suggest that some motion information is represented in terms of surface depth order.