UC Santa Cruz

Polystable phenomena have been extensively studied to understand the constructive nature of perception (e.g., the Necker cube, duck-rabbit, binocular rivalry). A new polystable phenomenon, illusory apparent motion (IAM), with unique properties was recently discovered (Davidenko et al., 2017). IAM is generated in randomly refreshing pixel arrays. As a result, IAM, unlike other polystable phenomena, affords potentially counterless interpretations of the pixel motion and observers may not automatically experience an initial interpretation, instead having to rely on self-generated initial percepts. These unique properties of IAM raise a plethora of questions.

In light of IAM’s unique properties, the four experiments presented here explore questions about the nature of subjective control of IAM. Experiments 1 and 2 ask whether observers can mentally control their perception of IAM (a feature common in other polystable phenomena). Experiment 1 explores this question using a motion priming and persistence task, based on the methods of Davidenko et al. (2017). Participants were presented with a series of priming frames that transitioned to frames of pure noise and reported with a single button press when the initial motion pattern appeared to change. Experiment 1 found that observers were able to mentally control IAM, evidenced by extended motion persistence when they were instructed to ‘hold’ and shortened motion persistence when they were instructed to ‘change.’ Experiment 2 explores the same question, but in a methodological context more in line with past subjective controls studies (Kohlers et al., 2008). For this task, participants were not assisted with motion primes, instead self-generating initial motion patterns, and reported their percepts dynamically throughout the trial. Experiment 2 found that participants were able to control their perception of IAM in this new, possibly more demanding, experimental context. Together, the results of Experiments 1 and 2 demonstrate that participants can subjectively control their perceptions of IAM.

Experiment 3 explored questions about the potentially countless interpretations of IAM: how many interpretations of IAM can observers perceive and subjectively control? Experiment 3 tested 14 different motion types, half of which were motion types not yet explored in IAM studies (i.e., containing expansion, contraction, and shearing motion patterns). For each trial, participants were informed about one of the 14 motion types of instruction and, for one block, reported when they happened to perceive the instructed motion. In another block, participants were instructed to try and ‘hold’ the instructed motion. Experiment 3 found that observers were able to perceive many and control a few interpretations of IAM, supporting previous assumptions that observers likely experience more interpretations of IAM than other polystable phenomena.

The last study, Experiment 4, explored whether it was possible to quantify some of the low- and high-level factors that can influence participants’ perception of IAM (e.g., subjective control, motion biases, motion coherence). To test this, participants were presented with two priming frames, followed by two test frames. The test frames were manipulated to present participants with (1) a nulling (prime-inconsistent) motion below and above their perceptual threshold, (2) with a facilitating (prime-consistent) motion below and above their perceptual threshold, and (3) with 0% motion. After each trial, participants reported the direction of motion that they perceived on the final two frames. Experiment 4 demonstrates that it’s possible to quantify a number of factors, including: the strength of the rebound bias, subjective control, motion nulling, and motion facilitation.

Taken together, Experiments 1-4 lay the initial groundwork for exploring subjective control of IAM. Together they demonstrate subjective control in a variety of task conditions, suggest which motion types participants can control, and quantify the strength of subjective control.