Challenging the distribution shift: Statically-induced direction illusion implicates differential processing of object-relative and non-object-relative motion

Abstract

The direction illusion is the phenomenal exaggeration of the angle between the drift directions, typically, of two superimposed sets of random dots. The direction illusion is commonly attributed to mutual inhibition between direction-selective cell populations (distribution-shift model). A second explanation attributes the direction illusion to the differential processing of relative and non-relative motion components (differential processing model). Our first experiment demonstrates that, as predicted by the differential processing model, a static line can invoke a misperception of direction in a single set of dots--a phenomenon we refer to as the statically-induced direction illusion. In a second experiment, we find that the orientation of a static line can also influence the size of the conventional direction illusion. A third experiment eliminates the possibility that these results can be explained by the presence of motion streaks. While the results of these experiments are in agreement with the predictions made by the differential processing model, they pose serious problems for the distribution-shift account of shifts in perceived direction.

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

“…When transparent motion RDKs were presented with a static line orthogonal to the motion stimulus' nonobject-relative component velocity, the DI was negated. Conversely, a substantial illusion was found when there was no line or when the line was parallel to the nonobject-relative motion component (Farrell-Whelan et al, 2012a).…”

“…Further support for the differential processing model was recently provided by Farrell-Whelan et al (2012a), who found that a static line could produce a shift in the perceived direction of a single set of dots: a ''staticallyinduced direction illusion'' reminiscent of the ''slalom effect'' (Cesàro & Agostini, 1998;Ito & Yang, 2013). A static line with endpoints that are obscured provides no positional reference cues for moving objects along the axis of its orientation (Farrell-Whelan et al, 2012a).…”

“…The population of neurons tuned to the direction bisecting the two presented directions is inhibited the most, since that population is equally responsive to both directions. At more acute angular separations, mutual inhibition between populations of neurons tuned to the two directions causes a lateral shift in the neuronal response distributions, such that the peaks of the distributions sit above directions with a wider angular separation than those physically present, resulting in an enlarged perceived direction difference (Farrell-Whelan et al, 2012a). Since neurons exhibiting inhibitory interactions have been found at many levels of the visual processing hierarchy, the distribution-shift model leaves open the question of the neural locus of the DI; varying accounts have suggested primary visual cortex (V1) (Hiris & Blake, 1996) or middle temporal area (MT) Kim & Wilson, 1997).…”

“…A static line with endpoints that are obscured provides no positional reference cues for moving objects along the axis of its orientation (Farrell-Whelan et al, 2012a). Correspondingly, the static line acts as a reference object for motion stimuli moving orthogonal to the line, but not parallel to it.…”

“…Marshak and Sekuler's (1979) original study utilized superimposed random dot kinematograms (RDKs); two sets of RDKs presented in tandem appear to be moving transparently over each other when the angular difference in their movement directions is sufficiently large, allowing the direction of a single set of dots to be perceptually extracted (Braddick et al, 2002). The transparent arrangement has been employed in the majority of DI studies that followed the original work of Marshak and Sekuler (e.g., Benton & Curran, 2003;Braddick et al, 2002;Chen, Matthews, & Qian, 2001;Dakin & Mareschal, 2000;Farrell-Whelan, Wenderoth, & Brooks, 2012a, 2012bGrunewald, 2004;Hiris & Blake, 1996;Rauber & Treue, 1999;Wiese & Wenderoth, 2007). In addition to transparent motion, the DI has been investigated using spatially segregated stimuli presenting target and inducer in a concentric center-surround configuration, with the central target set inside a surrounding annulus.…”