Illusory line motion is not caused by object-differentiating mechanisms or endogenous attention

Asymmetrical Pseudo-Extinction Phenomenon in the Illusory Line Motion

Illusory Line Motion (i.e., a static line, presented after a lateral cue, is perceived as movement in the opposite direction to the cue) has been used to study a phenomenon of perceptual asymmetry. We have demonstrated the presence of an illusion of leftward movement, even in the presence of bilateral symmetrical cues. We have classified this phenomenon as one of pseudo-extinction. The paradigm of the four experiments performed was always the same: a white line, briefly presented alone or preceded by one or two lateral cues (150 ms), was judged by a group of young participants to be moving either to one side or the other. The asymmetrical effect in the bilateral cue condition was observed with horizontal lines (Experiment 1 and 4), and not with vertical or oblique (Experiment 2 and 3). These results suggest that the effect is linked to the asymmetry of the horizontal spatial planum and the mechanisms of spatial attention. Experiment 4 verified whether the Illusory Line Motion involves the collicular pathway by using blue stimuli for the cues, which activate less the Superior Colliculus (SC), with negative results. We interpreted the asymmetrical pseudo-extinction phenomenon in terms of a right-space exogenous attention advantage.

Comparisons of flashILM, transformational apparent motion, and polarized gamma motion indicate these are three independent and separable illusions

Illusory line motion (ILM) refers to perceived motion in a bar when it is presented all at once. Explanations for ILM include low-level visual accounts, visual attention, and object tracking. These explanations tend to arise from studies using different protocols to induce ILM, based on the assumption that the same illusion is being generated. Using real motion in the same and in the opposite direction as the ILM quantifies the illusions from all protocols as the area between response curves for the left- and right-side inducers. This common measure enables testing of the assumption that two display configurations result in the same illusion. If there is a common underlying cause, an individual who shows a strong illusion in one situation should show a strong illusion in the other, but illusions that arise through different systems should not correlate. This approach has differentiated ILM induced by a flash (_flashILM) from ILM induced by matching the bar to an attribute of the inducing stimuli (transformational apparent motion, TAM). The former is thought to reflect attention, while the latter is thought to reflect object processing. Low-level visual explanations are often offered based on ILM that occurs when the bar is adjacent to only a single inducer (polarized gamma motion, PGM) rather than between two stimuli (_flashILM and TAM). The present study replicates the independence of _flashILM and TAM and shows that neither is related to PGM, suggesting that all three explanations for ILM are warranted and that the debates in the literature are conflating at least three different illusions.

Does Allocation of Attention Influence Relative Velocity and Strength of Illusory Line Motion?

In illusory line motion, presentation of a cue is followed by presentation of a nearby stationary line, and the line is perceived to “unfold,” “expand,” or “extend” away from the cue. Effects of the allocation of attention regarding where the cue or the line would be presented were measured in three experiments, and ratings of relative velocity and relative strength of illusory motion were collected. Findings included (a) relative velocity and relative strength decreased with increases in SOA from 50 to 450 ms, (b) relative velocity and relative strength were not influenced by whether illusory motion moved from one end of the line to the other or from both ends toward the middle of the line, (c) increased uncertainty regarding where the line would appear did not influence relative velocity or relative strength, and (d) valid pre-cues regarding the location of a cue resulted in faster relative velocity than did invalid pre-cues, but pre-cue validity did not influence relative strength. Implications of these findings for the relationship of such illusory motion and attention (e.g., divided attention, shifts in attended location) are considered.

Flash-induced forward and reverse illusory line motion in offset bars

Illusory line motion (ILM) refers to perception of motion in a bar that onsets or offsets all at once. When the bar onsets or offsets between two boxes after one of the boxes flashes, the bar appears to shoot out of the flashed box (_flashILM). If the bar offsets during the flash, it appears to contract into the flashed box (reverse ILM; rILM). Onset bars do not show rILM. Moreover, rILM and _flashILM are not correlated, indicating they are two different illusions. To date, rILM has only been studied using a 50-ms flash where the bar offsets 16.7 ms after flash onset. It is not clear if rILM is due to the 16.7-ms flash-bar-removal stimulus onset asynchrony (SOA) or due to the flash offsetting after the bar. The current studies explore these parameters to better understand the conditions that lead to rILM. The results suggest that _flashILM is sensitive to the temporal interval between flash onset and bar offset, while rILM appears to arise when the flash offsets after the bar has been removed regardless of the temporal interval between flash onset and bar removal. These results are consistent with _flashILM reflecting visual exogenous attention while rILM may reflect the low-level spreading of subthreshold activation radiating from the flashed box. The findings are incorporated into the recent work that suggests that the literature concerning ILM is possibly conflating a number of different illusions of line motion, including polarized gamma motion (PGM), transformational apparent motion (TAM), and exogenous attention induced motion (_flashILM).

Illusory line motion in onset and offset bars

Illusory line motion (ILM) refers to the perception of motion in a bar that is presented all at once next to an inducing stimulus. The experimental methods for producing and quantifying ILM are varied, and the resulting explanations are likewise at odds. The current study examined the explanations for ILM away from the inducing stimulus (bright or dark flash) using bars that either suddenly appear (onset bars) or suddenly disappear (offset bars). Real motion is used to cancel ILM, providing three measures to quantify ILM: the consistency of responding to only ILM in the absence of real motion; the distance between the points of subjective equality between ILM and the real motion; and the area between the curves relating perception of motion to the real and illusory conditions. ILM quantities for onset and offset bars are strongly correlated when the bar change occurs after the flash. However, onset bars presented during the flash do not show any evidence of ILM, whereas offset bars removed during the flash result in reverse ILM (rILM). Moreover, rILM and ILM are not correlated, suggesting they reflect two separate illusions. These results are consistent over the various measures of ILM.