Measuring the Attentional Speed-up in the Motion Induction Effect

Abstract

Motion induction is the illusory motion within an elongated stimulus, such as a bar or a line, when it is preceded by a priming stimulus next to one of its ends. Motion is away from this primer. The presentation of two priming spots at both ends of a stimulus bar results in motion away from both spots with a collision in the center of the bar. With a sufficiently long delay between the spots, motion will be seen only as away from the second spot. Similarly, in a bar with a luminance gradient an illusory motion is perceived as away from the high-luminance end, presumably due to the known dependence of neural processing speed on luminance. In the present study, these two illusory motions were made to oppose each other. The particular luminance gradient which would just cancel the motion induction effect when motion is seen optimally as away from the second spot (cancellation gradient) was determined, resulting again in a collision near the center of the bar. Furthermore, the luminance dependence of the reaction time to stimulus detection was measured in a separate experiment. Thus for each observer, the processing time difference associated with the cancellation gradient was established. This delta t then gives the amount of time by which processing is speeded up in motion induction due to the priming spot. In a simple model of motion processing it can also be identified as the built-in delay delta t of a typical Reichardt-type motion detector. With the present conditions, it varied between 14 and 19 msec for different observers for a bar length of 5.3 deg. In this way, we show not only that the priming effect in motion induction can be understood as a speed-up of neural processing, but also provide a way of measuring the times involved. In additional experiments, we examined the effect of bar length and luminance profile. These results allow us to estimate the gradients of the attentional fields.

Illusory line motion in onset and offset bars

“…Moreover, if a bar appears that is bright at one end and progressively dims along its length, motion occurs from the bright to the dim end (von Grünau, Racette, & Kwas, 1996); this occurs despite the fact that the entire bar presentation creates only a contrast increase. Furthermore, the motion is in the direction from the larger increase towards the smaller, so it is towards a tendency to decrease.…”

“…The fitting of a function to the percept scores in order to extract ILM PSE opens the door for many additional experimenter degrees of freedom, such as what function to fit (log linear as currently employed or Weibull as in von Grünau, Racette et al, 1996), how to fit it (least squares, maximum likelihood), and the criterion for deciding if a function provides a good fit. All of these decisions open up additional questions of appropriateness of the choice, which can complicate interpretation, become a source of distraction, and reduce the simplicity of comparison between studies.…”

“…Sometimes a subjective rating scale was used, where participants were asked to rate the strength of their motion perception (Christie, 2014;Christie & Klein, 2005). Luminance gratings (von Grünau, Racette, et al, 1996) have been used to produce presumed perceptual asymmetries resulting in motion in the opposite direction until a point of subjective equality is found, quantifying the illusion in terms of the luminance grating. Similarly, the bar has been presented in sections, towards or away from the flashed box, to quantify the illusion in terms of the amount of real motion required to reach the point of subjective equality (Bavelier et al, 2002;Crawford et al, 2010;Steinman, Steinman, & Lehmkuhle, 1995).…”

Does attention cause illusory line motion?

“…It has further been asserted that the orienting of attentional mechanisms toward the location of the luminance increase is the cause of the perceived motion within the line (Hikosaka et al, 1993b;von Grünau, Racette, & Kwas, 1996). Studies of temporal order judgments have shown that the orienting of attention produces an acceleration of arrival times in the vicinity of the attended locus (Schneider & Bavelier, 2003;Shore, Spence, & Klein, 2001;Stelmach & Herdman, 1991).…”

Catching the voltage gradient—asymmetric boost of cortical spread generates motion signals across visual cortex: a brief review with special thanks to Amiram Grinvald

“…Hence, it was hypothesized that the sensation of motion evoked by the subsequently flashed line could result from sequential suprathreshold activation mimicking real motion drawing away from the local cue. [17][18][19][20] Figure 2(c) shows cortical responses (in V1 of an anaesthetized cat) evoked by the spot when it was flashed alone. 20 Consistent with spreading along horizontal connections, postsynaptic subthreshold activity propagated at a speed of ∼0.1 m∕s (Refs.…”