2016-05-26 14:20:35

## Changes in early optic flow experiences across development and culture

### Florian Raudies, HP Research

Supported by NSF BCE-1147440, NSF BCS-1238599, NICHD U01-HD-076595

## Background

• What is optic flow?
• How does sensitivity to optic flow develop?
• How do infants' natural experiences with optic flow develop?
• Do the statistics of infants' natural experiences align with changes in sensitivity?

## Developmental/Cultural Factors

• Posture: Walking vs. Crawling
• Distance to ground surface
• Head pitch relative to ground
• Geometry: Typical distance to surfaces, objects; number of people, objects
• Moving through space: self vs. object motion

## Approach

• Simulating changes in optic flow due to changes in body size & posture, geometry
• Measuring flow experienced in natural contexts by head-mounted cameras

## Optic Flow Equation

$$\begin{pmatrix}\dot{x} \\ \dot{y}\end{pmatrix}=\frac{1}{z} \begin{pmatrix}-f & 0 & x\\ 0 & -f & y \end{pmatrix} \begin{pmatrix}{v_x{}}\\ {v_y{}} \\{v_z{}}\end{pmatrix}+ \frac{1}{f} \begin{pmatrix} xy & -(f^2+x^2) & fy\\ f^2+y^2 & -xy & -fy \end{pmatrix} \begin{pmatrix} \omega_{x}\\ \omega_{y}\\ \omega_{z} \end{pmatrix}$$

## 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

## 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

## Simulated Flow Speeds (m/s)

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

## Sample characteristics

Country Females Males Age (wks) Coded video Hrs
India 17 13 3-63 3.1 (0.5-6.0)
U.S. 15 19 4-62 4.6 (0.2-7.6)

Data & excerpts: http://databrary.org/volume/81

## Workflow

• Extract optic flow from video, (code repo)
• Human coders: is infant moving or stationary?
• How do flow speeds and patterns vary by
• Age
• Geography/Culture
• Moving/stationary status