The Wolfpack Effect: Perception of Animacy Irresistibly Influences Interactive Behavior
 
 
Here are some demonstrations of the various conditions discussed in the following paper:
Gao, T., McCarthy, G., & Scholl, B. J. (2010). The wolfpack effect: Perception of animacy irresistibly influences interactive behavior. Psychological Science, 21(12), 1845-1853.
These demonstrations are provided as Quicktime movies, which can be downloaded or viewed directly in most web-browsers. (To download a free Quicktime player, go here.) These movies are a bit large and choppy, but they should be sufficient to illustrate the basic conditions. As highly compressed versions of the original stimuli, these movies may not preserve the precise spatial and temporal characteristics of the originals.  
 
 
The Wolfpack Effect
Imagine a pack of predators stalking their prey. Such events appear to be richly animate, but why? An obvious cue is objective pursuit: the predators continually move towards their target. But not always: in some circumstances (e.g. when chasing a much larger animal), they may have to circle around their prey, in which case they may frequently be moving orthogonal to it (or even temporarily retreating), but still facing it. In other words, there may sometimes be a dissociation in such circumstances between the direction a predator is facing and the direction in which it is moving. Inspired by such natural phenomena, we predicted that the coordinated orientations of a group of moving shapes would automatically yield a percept of animacy when the shapes continually pointed towards a single target shape -- even if their actual motions were random.  
 
Animation S1.1: Basic Demonstration of the Wolfpack Effect (4.5 MB)
Each dart moves randomly on the display, but is always oriented towards the disc (which is being moved about by a human controller).  
 
Animation S1.2: Basic Demonstration of the 'Perpendicular' Control for the Wolfpack Effect (4.5 MB)
The trajectories of the darts and the disc are identical, but now the darts are consistently oriented orthogonal to the disc. This greatly weakens or destroys the effect.  
 
'Search-For-Chasing' Experiment
Observers had to detect whether one dart (the wolf) chased -- i.e. was consistently displaced towards -- another disc (the sheep). The darts' orientations and the behavior of the green square were thus task-irrelevant. The animations provided here depict only 'Chase-Present' trials. (On Chase-Absent trials, the wolf was still present and moved in the same manner, but was 'chasing' an invisible sheep.) We provide each animation in two versions. One approximates the displays seen by the observers, in which all darts were featurally identical. In the other 'Cheat' version, the wolf is drawn in red, and the sheep is drawn in green. This may help to orient readers to conditions in which it is otherwise difficult to detect the chasing, but note that observers only ever saw monochromatic darts. As reported in the paper, the Wolfpack condition was the only condition that impaired the ability to discriminate Chase-Present from Chase-Absent trials.

Animation S2.1: Wolfpack condition (Search-For-Chasing Experiment) (1.2 MB)
Animation S2.2: Wolfpack condition (Search-For-Chasing Experiment) [CHEAT] (1.2 MB)

Each dart is always oriented towards the green square.  
 
Animation S2.3: Perpendicular condition (Search-For-Chasing Experiment) (1.2 MB)
Animation S2.4: Perpendicular condition (Search-For-Chasing Experiment) [CHEAT] (1.2 MB)

Each dart is always oriented orthogonal to the green square.  
 
Animation S2.5: Match condition (Search-For-Chasing Experiment) (848 KB)
Animation S2.6: Match condition (Search-For-Chasing Experiment) [CHEAT] (976 KB)

Each dart is always oriented in the direction in which it is moving.  
 
Animation S2.7: Disc condition (Search-For-Chasing Experiment) (620 KB)
Animation S2.8: Disc condition (Search-For-Chasing Experiment) [CHEAT] (756 KB)

To serve as a baseline, each dart was replaced with an orientation-less disc.  
 
'Don't-Get-Caught' Experiment
Participants controlled the movement of the green disk (the sheep) using the mouse to avoid being touched by the 'wolf' -- a disc that consistently moved toward the sheep -- while all other discs and darts moved randomly and were task-irrelevant. This task cannot be readily illustrated in premade animations, since it was inherently interactive. Here, instead, we depict 'played back' trials in which a sample participant completed the task. We again provide each animation in two versions. One approximates the displays seen by the observers, in which all darts were featurally identical. In the other 'Cheat' version, the wolf is drawn in red, and the sheep is drawn in green. This may help to orient readers to the subtler conditions, but note that our observers only ever saw monochromatic darts. As reported in the paper, the Wolfpack condition impaired participants' ability to detect and avoid the wolf relative to the Perpendicular condition.

Animation S3.1: Wolfpack condition (Don't-Get-Caught Experiment) (852 KB)
Animation S3.2: Wolfpack condition (Don't-Get-Caught Experiment) [CHEAT] (852 KB)
Each dart is always oriented towards the user-controlled green disc.  
 
Animation S3.3: Perpendicular condition (Don't-Get-Caught Experiment) (1.3 MB)
Animation S3.4: Perpendicular condition (Don't-Get-Caught Experiment) [CHEAT] (1.3 MB)
Each dart is always oriented orthogonal to the user-controlled green disc.  
 
'Leave-Me-Alone' Experiment
Participants moved a green disc about the display attempting to avoid contact with any of the white objects. Each quadrant contained 3 white objects. In two Wolfpack quadrants, each object was always oriented towards the user-controlled green disc. In two Perpendicular quadrants, each object was always oriented orthogonal to the user-controlled disc. This task cannot be readily illustrated in premade animations, since it was inherently interactive. Here, instead, we depict 'played back' trials in which a sample participant completed the task. As described in the paper, observers spent less time with the disc in the Wolfpack quadrants than in the Perpendicular quadrants.

Animation S4.1: Darts (Leave-Me-Alone Experiment) (5.1 MB)
Orientation was depicted via the direction in which each dart was pointed.  
 
Animation S4.2: Eyes (Leave-Me-Alone Experiment) (5.1 MB)
Orientation was depicted by the placement of two small circles on each otherwise-orientationless disc, which appeared to be eyes 'looking' in a particular direction.  
 
Animation S4.3: Flashing Control (Leave-Me-Alone Experiment) (3.8 MB)
In a control experiment to show that these effects were not due to attention capture, two quadrants contain discs, and two other quadrants contain flashing discs. Observers spent no more time in either type of quadrant.  
 
Hybrid 'Don't-Get-Caught'/'Leave-Me-Alone' Experiment
In this hybrid of the Don't-Get-Caught and Leave-Me-Alone tasks, participants controlled the movement of the green disc using the mouse to avoid touching any of (1) the white darts, (2) the display border, or (3) the red 'wolf' disc that consistently moved toward the user-controlled green disc. Unlike the initial Don't-Get-Caught task, here participants did not struggle to determine the wolf's identity, since it was always displayed in a unique color. Unlike the initial Leave-Me-Alone task, one of the objects in the display (viz. the wolf) had a motion trajectory that was correlated to the movement of the user-controlled disc. This task cannot be readily illustrated in premade animations, since it was inherently interactive. Here, instead, we depict 'played back' trials in which a sample participant completed the task. As reported in the paper, performance was impaired in the Wolfpack-to-Sheep condition relative to both the Perpendicular-to-Sheep condition and the Wolfpack-to-Wolf condition -- and these effects were considerably larger than in the previous experiments. This demonstrates that the Wolfpack effect is a social effect: it matters in such situations whether the wolfpack is facing you instead of a third party.

Animation S5.1: Wolfpack-to-Sheep condition (Hybrid Experiment) (1.1 MB)
Each dart is always oriented towards the user-controlled green disc.  
 
Animation S5.2: Perpendicular-to-Sheep condition (Hybrid Experiment) (1.2 MB)
Each dart is always oriented orthogonal to the user-controlled green disc.  
 
Animation S5.3: Wolfpack-to-Wolf condition (Hybrid Experiment) (1.2 MB)
Each dart is always oriented towards the red 'wolf' disc.