Whether dots moving in two directions appear coherent or transparent depends on directional biases induced by surrounding motion

Abstract

When two random-dot patterns moving in different directions are superimposed, motion appears coherent or transparent depending on the directional difference. In addition, when a pattern is surrounded by another pattern that is moving, the perceived motion of the central stimulus is biased away from the direction of the surrounding motion. That phenomenon is known as induced motion. How is the perception of motion coherence and transparency modulated by surrounding motion? It was found that two random-dot horizontal motions surrounded by another stimulus in downward motion appeared to move in two oblique directions: left-up and right-up. Consequently, when motion transparency occurs, each of the two motions interacts independently with the induced motion direction. Furthermore, for a central stimulus consisting of two physical motions in left-up and right-up directions, the presence of the surrounding stimulus in a vertical motion modulated the perceptual solution of motion coherence/transparency such that if interactions with an induced motion signal narrow the apparent directional difference between the two central motions, then motion coherence is preferred over motion transparency. Therefore, whether a moving stimulus is perceived as coherent or transparent is determined based on the internal representation of motion directions, which can be altered by spatial interactions between adjacent regions.

Directional Limits on Motion Transparency Assessed Through Colour-Motion Binding

“…To determine the extent to which discrimination in transparent motion is worse than for nontransparent motion, we ran a control experiment where the motions were not superimposed but instead occupied adjacent spatial regions, and colour-motion coherence was fixed at 100%. Note that, although they were no longer transparent, the two motions in the centre-surround annular display should still be prone to the same interactions underlying direction repulsion, as many studies using this type of stimulus arrangement have shown (e.g., Chen et al., 2014; Kim & Wilson, 1997; Takemura et al., 2011; Wiese & Wenderoth, 2010). Data from five participants as well as the group average in the control experiment are plotted in Figure 5.…”

“…The representation of such multiple velocity fields at the same region of space is a challenging computational feat, both for the visual system as well as for models that attempt to simulate it (Braddick, Wishart, & Curran, 2002; Garcia & Grossman, 2009; McDonald, Clifford, Solomon, Chen, & Solomon, 2014; Qian, Andersen, & Adelson, 1994; Snowden, Treue, Erickson, & Andersen, 1991; Snowden & Verstraten, 1999). As such, the constraints by which the perception of transparency collapses and the separate moving surfaces are instead misperceived as a single or ‘coherent’ pattern comprise an important focus of research (Suzuki & Watanabe, 2009; Takemura, Tajima, & Murakami, 2011; Williams & Sekuler, 1984).…”

Structure in motion: visual motion perception as online hierarchical inference

“…Solid blue: predicted biphasic function for smaller opening angles. (h)–(l) Extended experiment from [39] which surrounds the two central RDKs with additional RDKs in an annulus. The hierarchical inference model replicates human perception in various conditions.…”

“…The hierarchical inference model replicates human perception in various conditions. (h) A surround with dots moving vertically both up- and downwards (“bi-directional surround” in [39], indicated by orange arrows in the top-left sketch’s annulus) causes no repulsion in the perceived directions of horizontally moving RDKs in the center (darker orange arrows in the top-left sketch’s center). Our model replicates this perception as shown in the histogram of 200 trial repetitions.…”

Determinants of the direction illusion: Motion speed and dichoptic presentation interact to reveal systematic individual differences in sign

“…Braddick et al (2002), using a similar stimulus, found that the largest illusion magnitude was produced by a 458 inducer, while angles of 11.258 and 22.58 resulted in a small direction attraction effect. However, overlaid dot patterns presented with a small directional separation are perceived as a single surface moving in the vector average of the two directions, rather than as overlaid patterns moving in different directions (e.g., Felisberti & Zanker, 2005;Greenwood & Edwards, 2007;Mather & Moulden, 1980;Smith, Curran, & Braddick, 1999;Takemura, Tajima, & Murakami, 2011). Hence attraction measured at such small inducing angles may more accurately reflect a strategy of motion vector averaging, rather than direction attraction per se.…”