We formulate a model for object-centered motion processing that explains non-retinotopic motion percepts observed psychophysically

Clarke, Aaron Michael

Herzog, Michael

Ogmen, Haluk

Infoscience - École polytechnique fédérale de Lausanne

A Model for Non-Retinotopic Processing Aaron Clarke1, Haluk Öğmen2 & Michael H. Herzog1     1. Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland   2. Electrical &Computer Engineering, Cullen College of Engineering, University of Houston, USA Introduction:  A reflector on a moving bicycle wheel appears to follow a circular path even though its physical trajectory is actually cycloidal. The cycloidal trajectory is perceived only when the bicycle is invisible. Hence, the brain interprets motion not in a purely retinotopic manner but according to a non-retinotopic reference frame that takes into account neighboring motion patterns. http://lpsy.epfl.ch   This work was supported by the Swiss National Science Foundation (SNF).                Corresponding author: aaron.clarke@epfl.ch Ternus-Pikler Display:  • How can non-retinotopic motion perception be studied experimentally? • The Ternus-Pikler display directly pits retinotopic and non-retinotopic processes against each other and thus provides a useful probe for testing retinotopic versus non-retinotopic processing. A. With an ISI of 210 ms, the three black disks appear to move back and forth as a group.  The central disk’s white dot appears to rotate. B. Removing the outer disks yields the percept of two stationary disks whose dots move up-down and left-right. C. With an ISI of 0 ms, the outer-most disk appears to jump from one side of the display to the other, while the central two disks appear stationary. The dot motions are again perceived to move up-down and left-right.  Model:  • How can non-retinotopic motion perception be modeled? • Pooresmaeili, Cicchini, Morrone and Burr, (2012) proposed a one-stage model based on spatio-temporal filtering. However, the model has some methodological problems and lacks generalizability (Clarke, Repnow, Öğmen and Herzog, in press). A. Group motion B. No motion C. Element motion Percept Percept Percept Stimulus Stimulus Stimulus Time 120 ms ISI 210 ms 120 ms 120 ms 120 ms ISI 210 ms ISI 210 ms Space Time Time 120 ms ISI 210 ms 120 ms 120 ms 120 ms ISI 210 ms ISI 210 ms 120 ms ISI 0 ms 120 ms 120 ms 120 ms ISI 0 ms ISI 0 ms Space Space Frame 2 edges Extract One Group Convolve Threshold Potential correspondences … Frame 1 Frame 2 Frame 1 Frame 2 Determine unique matches using Dawson (1991) The model also nicely handles other conditions established by Ternus (1926).  Black disks mark time 1 positions, while white transparent disks mark time 2 positions.  Arrows denote correspondence matches.  All correspondence matches are consistent with human percepts, except for the top-left sub-plot.  References:  • Clarke, A. M., Repnow, M., Öğmen, H. & Herzog, M. H. (in press). Does Spatio-Temporal Filtering Account for Non-Retinotopic Motion Perception? Comment on Pooresmaeili, Cicchini, Morrone, and Burr (2012). Journal of Vision. • Pooresmaeili, A., Cicchini, G. M., Morrone, M. C., & Burr, D. (2012). “Non-retinotopic processing” in ternus motion displays modeled by spatiotemporal filters. Journal of Vision, 12(1), 1-15. Frame 1 Grouped Edges Results: ISI = 0 ms ISI = 210 ms Extract motion vectors Extract motion vectors Subtract local disk motions Subtract local disk motions 𝑃 𝑡𝑖 , 𝑡𝑗 ∈ 𝐶|𝑟, 𝜃1, 𝜃2𝑃 𝑡𝑖 , 𝑡𝑗 ∈ 𝐶 |𝑟, 𝜃1, 𝜃2=𝑃 𝑟, 𝜃1, 𝜃2| 𝑡𝑖 , 𝑡𝑗 ∈ 𝐶 𝑃 𝑡𝑖 , 𝑡𝑗 ∈ 𝐶𝑃 𝑟, 𝜃1, 𝜃2| 𝑡𝑖 , 𝑡𝑗 ∈ 𝐶 𝑃 𝑡𝑖 , 𝑡𝑗 ∈ 𝐶  r q1 q2 q3 ti tj 𝐶 = 𝛿 ∙ 𝜔𝑁𝑁 ∙ 𝑁𝑁 + 𝜔𝑅𝑉 ∙ 𝑅𝑉 + 𝜔𝐸𝐼 ∙ 𝐸𝐼  Nearest Neighbour Relative Velocity Element Integrity 𝜔𝑁𝑁 𝐼𝑆𝐼 =  erf( (ISI−41.47)) ∙  0.12 ) ∙ 0.5+0.5 Connectivity matrix Generalization: Time 1 Time 2 Retinotopic space Reference frame Non-retinotopic manifold Next, the temporal correspondence problem is solved: • Here, we propose a two-stage model that first establishes a motion-based dynamic reference frame and then estimates motion signals within this reference frame. • In the Ternus-Pikler display, non-retinotopic motion percepts are explained  by establishing a reference frame based on the motions of the disks and then determining the dot motions within this reference frame.  Edge filtering and grouping:  • First, edges are extracted by standard procedures. • Next, the edges are grouped based on proximity and good continuation. The model does a good job at reproducing the human percepts. At the 0 ms ISI, the model produces up-down and left-right dot percepts (see arrows).  At the 210 ms ISI the model produces a circular dot motion percept. 

A Model for Non-Retinotopic Processing

http://infoscience.epfl.ch/record/199402/files/ClarkeECVP2013v10.pdf

A Model for Non-Retinotopic Processing

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