New insights and a computational model for understanding induced motion revealed through novel variants of the Flying Bluebottle Illusion

Abstract

The Flying Bluebottle Illusion is a compelling example of how the perceived trajectory of moving objects can be greatly influenced by other motion sources in the visual scene. In this article, we present a series of simplified variants of the Flying Bluebottle Illusion in which the true motion of a target is a circular orbit around a central point. However, when a similar but offset orbiting motion trajectory is added to a set of surrounding inducers, the perceived trajectory of the target is drastically altered in both extent and direction. In other words, the perceived orbiting motion of the target is "pulled" and distorted by the orbiting motion of the inducers. For simplicity's sake, we refer to the illusory effect revealed by these dueling orbits as the Dueling Orbit Illusion. These simplified variants lend themselves to empirical study with resultant effects that can be readily modeled. Here, we present a series of case examples for how the parameters of the stimuli may be varied to yield predictable effects, describe a straightforward computational model for quantifying the magnitude of the contextual influence, and discuss how the model may be leveraged to gain insight into the phenomenon of induced motion across a range of within and between observer domains.

Keywords: induced motion; motion contrast; motion perception; relative motion; visual illusion.

Figure 1.

Comparison of the veridical (left, see Movie 1) and approximate perceived (right) motion trajectory of the central target for Movies 2–6. See Figure 2 for more details on predicting the perceived trajectory of the target under different viewing conditions.

Figure 2.

(a) A computational model showing how the perceived path of the target (green) is approximated by averaging the relative trajectory (magenta) and the eye-centered target path (black). (b) A detailed example for Movie 6, under conditions of stable peripheral fixation (green fixation spot in Movie 6). An equal weighting (k = .5) of the eye-centered and relative trajectories predicts the triangular perceived target path. (c) The eye-centered target path (black), relative path (magenta), and equally-weighted average (green, k = .5) for Movies 2–5. Pursuit of the target biases the perceived path in favor of the eye-centered path (.5 < k < 1), whereas pursuit of an inducer biases the perceived path in favor of the relative path (0 < k < .5). Note that the actual path of the speed, direction, and phase of the inducers and target differs across movies, but this is accounted for in the relative trajectory trace.