2015-08-10

What Accounts for Developmental Shifts in Optic Flow Sensitivity?

Background

  • What is Optic Flow?
  • How Does Optic Flow Sensitivity Develop?

What is Optic Flow?

  • Structured pattern of visual motion generated by observer movement
  • Radial, rotational, translational/laminar patterns

How Does Optic Flow Sensitivity Develop?

  • Sensitivity at birth
  • Infants more sensitive to fast, translational flow
  • Adults more sensitive to slow, radial flow

Natural Scene Statistics of Optic Flow

This Study Asks

  • What are the statistics of infants' optic flow experiences in more natural contexts?
  • Do the statistics help explain development in sensitivity?
  • Do cultural differences (home geometries, carrying practices, etc.) carry much weight?
  • Are fast, translational flows common?

Approach

  • Simulating changes in optic flow due to changes in body size & posture, geometry
  • Empirical measurement of flow experienced in natural contexts

Theoretical Framework

  • What changes in development or culture might influence optic flow?
  • Posture: Walking vs. Crawling
    • Distance to ground surface
    • Head pitch relative to ground
  • Geometry: Typical distance to surfaces, objects
\(\begin{pmatrix}\dot{x} \\ \dot{y}\end{pmatrix}=\frac{1}{z} \begin{pmatrix}-f & 0 & x\\ 0 & -f & y \end{pmatrix} \begin{pmatrix}{v_x{}}\\ {v_y{}} \\{v_z{}}\end{pmatrix}+ \frac{1}{f} \begin{pmatrix} xy & -(f^2+x^2) & fy\\ f^2+y^2 & -xy & -fy \end{pmatrix} \begin{pmatrix} \omega_{x}\\ \omega_{y}\\ \omega_{z} \end{pmatrix}\)

Parameters For Simulation

Parameter Crawling Infant Walking Infant
Eye height 0.30 m 0.60 m
Locomotor speed 0.33 m/s 0.61 m/s
Head tilt 20 deg 9 deg


Kretch, Franchak, & Adolph (2014), http://dx.doi.org/10.1111/cdev.12206

Parameters for Simulation

Geometric Feature Distance
Side wall +/- 2 m
Side wall height 2.5 m
Distance of ground plane 32 m
Field of view width 60 deg
Field of view height 45 deg

Simulating Flow Fields

Flow Direction Distributions by Geometry & Posture

Flow Speeds By Geometry and Posture

\(\chi^2(20)\): ground: 920.8292078, room: 1476.1183605, side-wall: 958.7145051, and two-walls: 1110.3179808.

Mean Simulated Flow Speeds By Posture and Geometry

Type of Locomotion Ground Plane Room Side Wall Two Walls
Crawling 14.41 14.42 14.43 14.62
Walking 9.38 8.56 7.39 9.18

Empirical Measurements of Optic Flow

  • First-person videos from head-mounted cameras
  • 20 infants, 41 days to 13.2 mos
  • Chennai, India & Bloomington, Indiana
  • Data: http://databrary.org/volume/81

Cultural Differences in Segment Durations

Segment Durations

Normalized Durations as \(p\)(total-time)

Natural Scene Statistics for Optic Flow

  • Selected 10 5 s segments/participant, both moving and stationary
  • Estimated frame by frame flow fields
  • Details in Raudies & Gilmore 2014

Speed Distributions

Comparing Shapes of (Trimmed) Speed Distributions

  • Fit \(\gamma\) distribution to trimmed (0,100) speed histograms

\(f(x;k,\theta) = \alpha\frac{x^{k-1}e^{-\frac{x}{\theta}}}{\theta^k\Gamma(k)}\)

\(\alpha\), amplitude; \(\kappa\), shape; and \(\theta\), scale parameters.

Illustrative Speed Histograms - 6 weeks

Illustrative Speed Histograms – 34 weeks

Illustrative Speed Histograms – 58 weeks

Fitted \(\kappa\) Parameters

Fitted \(\alpha\) Parameters

Fitted \(\theta\) Parameters

Summary: Empirical Flow Speed Effects

  • Fast speeds (> 100 deg/s) common
  • Moving ≠ Stationary
  • Broad distribution: \(\kappa\), \(\alpha\)(moving) > \(\kappa\), \(\alpha\)(stationary)
  • U.S. ~ India

Empirical Pattern Distributions

  • Correlation with 'canonical' flow patterns
  • radial
  • rotational
  • translational

Pattern Correlation Results

Pattern Correlation Results by Country

Moving Laminar ≠ Stationary Laminar in 13/22 infants.

Conclusions: Simulation

  • Posture influences optic flow speeds & patterns
    • Crawling: faster speeds, more translational flow
    • Proximity to ground and pitch of head
    • Geometry matters relatively little

Conclusions: Empirical Data

  • Time stationary >> time in motion
  • Time stationary declines with age (India)
  • Fast speeds, broad speed distributions
  • Individual differences in moving vs. stationary speed distributions
  • Laminar flow >> radial or rotational flow, especially when stationary
  • Replicates and extends Raudies & Gilmore '12, '14

Questions to Ponder

  • How might optic flow experiences shape perception?
    • Differences between self vs. other-produced motion?
    • Influence of independently moving objects/people?
  • How do optic flow experiences shape brain responses?

Children's responses to time-varying flow

Adults' reponses to time-varying flow

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