Neural Correlates of Illusory Line Motion

Abstract

Illusory line motion (ILM) refers to a motion illusion in which a flash at one end of a bar prior to the bar's instantaneous presentation or removal results in the percept of motion. While some theories attribute the origin of ILM to attention or early perceptual mechanisms, others have proposed that ILM results from impletion mechanisms that reinterpret the static bar as one in motion. The current functional magnetic resonance imaging study examined participants while they made decisions about the direction of motion in which a bar appeared to be removed. Preceding the instantaneous removal of the bar with a flash at one end resulted in a motion percept away from the flash. If this flash and the bar's removal overlapped in time, it appeared that the bar was removed towards the flash (reverse ILM). Independent of the motion type, brain responses indicated activations in areas associated with motion (MT+), endogenous and exogenous attention (intraparietal sulcus, frontal eye fields, and ventral frontal cortex), and response selection (ACC). ILM was associated with lower percept scores and higher activations in ACC relative to real motion, but no differences in shape-selective areas emerged. This pattern of brain activation is consistent with the attentional gradient model or bottom-up accounts of ILM in preference to impletion.

Illusory line motion in onset and offset bars

“…Consistent with the attentional aspects of the explanation for ILM are the findings that the neural networks associated with visual attention are activated by these two boxes, flash, and bar type displays (Hamm et al, 2014;Tanabe & Yanagida, 2002). Moreover, ILM has been shown to be weaker in people diagnosed with schizophrenia (Crawford et al, 2010), a disorder long known to be associated with deficits in visual attention (Kraepelin, 1919).…”

“…This is called polarized gamma motion (Kanizsa, 1979), although in similar displays von Grünau and Faubert (1994) referred to this as motion induction. Although the presented object may be of any shape (Kanizsa, 1979), for convenience and to coincide with the current study and recent literature (Christie & Barresi, 2002;Christie & Klein, 2005;Crawford et al, 2010;Crawford, Kean, Klein, & Hamm, 2006;Downing & Treisman, 1997;Hamm et al, 2014;Hamm & Klein, 2002;Hikosaka, Miyauchi, & Shimojo, 1993a, 1993b, 1993cvon Grünau & Faubert, 1994), the object that undergoes illusory motion is referred to as the bar, because this object is generally rectangular with the motion directed along the long axis. The existing object that induces the illusory motion in the bar is referred to as the box, because the inducing object is typically a solid square.…”

“…When a preexisting bar is removed from between two boxes following the flash, the illusory motion of the disappearing bar is also away from the flashed box (Crawford et al, 2010;Hamm et al, 2014). This is unlike polarized gamma motion where the motion is towards the single box when an existing bar is removed in the absence of a flash (Kanizsa, 1979); there may be separate underlying causes behind polarized gamma motion and illusory line motion away from a flash.…”

“…If the bar is removed after the flash is over the motion is away from the flash (Crawford et al, 2010;Hamm et al, 2014); however, if the bar is removed during the flash then the motion is towards the flash (Hamm et al, 2014); this is reverse ILM (rILM). While some have suggested that attention may result in prolonging existing visual signals (Schmidt & Klein, 1997), which would bring rILM under an attentional explanation, it does not explain why offset bars produce rILM during the flash but ILM after the flash.…”

“…It appears, therefore, that in the literature ILM may refer to as many as four separate illusions of motion: 1) gamma motion (Kanizsa, 1979) that could reflect a gradient of activity radiating from the centre of mass of an object; 2) polarized gamma motion, which could reflect shifts of the centre of mass (Zanker, 1997), contrast counter-change (Hock & Nichols, 2010), and/or increased activity that spreads out from a visual stimulus (Jancke et al, 2004) resulting in faster detection of nearby onset stimuli and prolonged perception of offset stimuli; 3) motion away from a box when the bar matches a physical attribute (colour, luminance, size) of the box (Corballis et al, 2002;Faubert & von Grünau, 1995;Hock & Nichols, 2010), referred to as attribute priming, which may reflect contrast counter-change; and 4) motion away from a flashed box towards a nonflashed box, which may reflect an attentional gradient of prior entry benefits centred on the flash (Hamm et al, 2014;Hikosaka et al, 1993aHikosaka et al, , 1993bHikosaka et al, , 1993c. As a collection, these may describe how the visual system interprets incoming visual information to maximize the detection of actually moving stimuli.…”