Feature Tracking Motion Research Articles

The Role of Feature Tracking in the Furrow Illusion.

In the furrow illusion (Anstis, 2012), the perceived path of a moving target follows the veridical path orientation when viewed foveally, but follows the orientation of the texture when viewed peripherally. These radically different motion percepts depending on whether the stimulus is viewed foveally or peripherally has led Anstis to conclude that the furrow illusion reveals “profound differences in the way that the periphery and fovea process visual motion.” In the current study, we rather argue that the different percepts can be explained by reduced position acuity with eccentricity and therefore do not imply different ways of processing motion per se. If feature tracking, which is position-based, is involved in the perception of the veridical motion direction, then impairing the feature tracking motion system should strengthen the illusion. To reduce contribution of the feature tracking motion system, we used a crowding paradigm consisting in presenting many nearby targets. We found that under crowding conditions, the furrow illusion was stronger. We conclude that feature tracking was involved in the perception of the veridical motion direction, which is compatible with the hypothesis that the different motion percepts at fixation and in the periphery are due to a reduced position acuity with eccentricity affecting feature tracking, not to different ways of processing motion per se.

The temporal efficiency function of the energy-based and feature tracking motion systems

The temporal efficiency function of the energy-based and feature tracking motion systems

No dedicated second-order motion system

The existence of a second-order motion system distinct from both the first-order and feature tracking motion systems remains controversial even though many consider it well established. In the present study, the texture contribution to motion was measured within and beyond the spatial acuity of attention by presenting the stimuli in the near periphery where the spatial resolution of attention is low. The logic was that when moving elements are too close one to another for attention to individually select them (i.e., crowding), it is not possible to track them. To test the existence of a dedicated second-order motion system, the texture contribution to motion was measured when neutralizing both the feature tracking motion system and the contribution of the first-order motion system due to preprocessing nonlinearities introducing residual distortion products. When the contribution of distortion products was not neutralized, texture substantially contributed to motion for spatial frequencies within and beyond the spatial acuity of attention. When neutralizing the contribution of distortion products, texture substantially contributed to motion for spatial frequencies within the spatial acuity of attention, but not for spatial frequencies beyond the spatial acuity of attention. We conclude that there is no dedicated second-order motion system; the texture contribution to motion is mediated solely by the first-order (due to residual distortion products) and feature tracking (at frequencies within spatiotemporal acuity of attention) motion systems.

Feature tracking and aging

There are conflicting results regarding the effect of aging on second-order motion processing (i.e., motion defined by attributes other than luminance, such as contrast). Two studies (Habak and Faubert, 2000; Tang and Zhou, 2009) found that second-order motion processing was more vulnerable to aging than first-order motion processing. Conversely, Billino et al. (2011) recently found that aging affected first- and second-order motion processing by similar proportions. These three studies used contrast-defined motion as a second-order stimulus, but there can be at least two potential issues when using such a stimulus to evaluate age-related sensitivity losses. First, it has been shown that the motion system processing contrast-defined motion varies depending on the stimulus parameters. Thus, although all these three studies assumed that their contrast-defined motion was processed by a low-level second-order motion system, this was not necessarily the case. The second potential issue is that contrast-defined motion consists in a contrast modulation of a texture rich in high spatial frequencies and aging mainly affects contrast sensitivity at high spatial frequencies. Consequently, some age-related sensitivity loss to second-order motion could be due to a lower sensitivity to the texture rather than to motion processing per se. To avoid these two potential issues, we used a second-order motion stimulus void of high spatial frequencies and which has been shown to be processed by a high-level feature tracking motion system, namely fractal rotation (Lagacé-Nadon et al., 2009). We found an age-related deficit on second-order motion processing at all temporal frequencies including the ones for which no age-related effect on first-order motion processing was observed. We conclude that aging affects the ability to track features. Previous age-related results on second-order and global motion processing are discussed in light of these findings.

No second-order motion system sensitive to high temporal frequencies

The existence of a second-order motion pathway, distinct from both the first-order luminance pathway and the high-level feature tracking motion system, remains controversial. Two key arguments support its existence: second-order motion is perceived at temporal frequencies too high to be tracked and sensitivity is independent of the relative phase between superimposed luminance- and contrast-modulated gratings. The later argument is typically used to reject the hypothesis that the contrast-modulation contribution to motion is due to early nonlinearities introducing luminance artifacts. But this argument is only valid if the nonlinearities are homogenous across luminance motion detectors; it does exclude the possibility that compressive nonlinearities precede some luminance motion detectors and expansive nonlinearities precede others. In the current study, to neutralize the impact of such opposing nonlinearities, we superimpose a luminance-modulated grating with a high contrast contrast-modulated grating so that some luminance artifacts would sum with the luminance-modulated grating and others would subtract resulting in no net gain. The gratings were drifting in the same direction at a temporal frequency too high to be tracked (15Hz) and their relative phase was systematically varied. Observers were asked to null the net perceived motion by adjusting the contrast of another luminance-modulated grating drifting in the opposite direction. The contrast-modulation contribution to motion was estimated as the contrast difference between the two opposing luminance gratings when no net motion was perceived. Results showed no effect of phase and the contrast-modulation significantly contributed to motion when the contrast of the superimposed grating was low, but not when it was high (i.e. no net motion was perceived when both luminance gratings had the same contrast). We conclude that our sensitivity to contrast-modulated motion at temporal frequencies too high to be tracked is due to early opposing nonlinearities differing across luminance motion detectors, not to a second-order motion pathway. Meeting abstract presented at VSS 2012

The neural correlate of a higher-order feature-tracking motion system revealed by fMRI

The neural correlate of a higher-order feature-tracking motion system revealed by fMRI