Neural correlates of radial frequency trajectory perception in the human brain

Abstract

Radial frequency (RF) motion trajectories are visual stimuli that consist of a difference of Gaussians moving along a closed trajectory defined by a sinusoidal variation of the radius relative to a circular path. In the current study, multivoxel fMRI analyses demonstrated that spatial patterns of activity in visual regions V2, V3, and MT can predict RF motion trajectory shape regardless of whether an observer can behaviorally identify the shape or not. This result suggests that processing in these regions is concerned with local properties of the trajectories and not directly linked with a conscious percept of global trajectory shape. Whole-brain analyses show that RF motion trajectories also evoke premotor and posterior parietal cortical activity that may be a neural correlate of shape recognizability. Further, comparisons with activity evoked by static versions of the RF shapes reveal cue-invariant processing in regions of the posterior parietal and occipitotemporal cortices. Interestingly, the RF motion trajectories evoke patterns of dorsal visual stream cortical activity typical of visually guided movement preparation or action observation, suggesting that these stimuli may be processed as potential motor actions rather than as purely visual experiences.

The effect of spatiotemporal displacement on the integration of shape information

“…Rainville, Yourganov, and Wilson (2005) found BOLD responses in lateral-occipital complex (LOC) increased with increasing deviation from circular (i.e., amplitude) for static patterns and suggested this was an indication of the integration of shape information in this region. Furthermore, Gorbet et al (2014) found significantly more activation in LOC for low-frequency RF patterns (which demonstrate global integration) than for high frequency patterns (which demonstrate local processing). This result was found for both static and motion RF patterns, which they suggested indicates a common area of processing (Gorbet et al, 2014).…”

“…Furthermore, Gorbet et al (2014) found significantly more activation in LOC for low-frequency RF patterns (which demonstrate global integration) than for high frequency patterns (which demonstrate local processing). This result was found for both static and motion RF patterns, which they suggested indicates a common area of processing (Gorbet et al, 2014).…”

“…There are, however, some differences in the processing of static RF patterns and motion RF patterns. Behavioral results from Gorbet et al (2014) found that observers were unable to discriminate between high frequency motion RFs (RF9 and RF10), but were able to do so for the same frequency static patterns. Additionally, Wilson and Fung (2016) investigated the effect of discontinuities on motion RF patterns.…”

“…Thus, Or et al (2011 suggested these stimuli were processed in motion regions of the brain. Gorbet, Wilkinson, and Wilson (2012) and Gorbet, Wilkinson, and Wilson (2014), using fMRI, suggested their data supported the view that these patterns are processed in motion regions of the brain, however, they were unable to rule out the possibility that motion RFs were actually being processed as form information due to temporal integration of motion streaks.…”

“…The similarity in performance for the motion RF, moving slit, and moving pattern conditions, suggests a common mechanism involved in the processing of these stimuli. Therefore, we considered a possibility suggested by Gorbet et al (2014), in which ''motion streaks'' (Geisler, 1999) produce form information that is combined using the same mechanisms as those that underpin processing of contour-defined patterns. However, Wilkinson et al (2016) provide evidence against this explanation, as they found no effect on observer thresholds when they changed the duration of presentation (i.e., the average speed of motion) or contrast of the dot used for their motion RF stimulus, both of which were designed to change the length of motion streaks.…”