Global motion perception in 2-year-old children: a method for psychophysical assessment and relationships with clinical measures of visual function

Abstract

Purpose: We developed and validated a technique for measuring global motion perception in 2-year-old children, and assessed the relationship between global motion perception and other measures of visual function.

Methods: Random dot kinematogram (RDK) stimuli were used to measure motion coherence thresholds in 366 children at risk of neurodevelopmental problems at 24 ± 1 months of age. RDKs of variable coherence were presented and eye movements were analyzed offline to grade the direction of the optokinetic reflex (OKR) for each trial. Motion coherence thresholds were calculated by fitting psychometric functions to the resulting datasets. Test-retest reliability was assessed in 15 children, and motion coherence thresholds were measured in a group of 10 adults using OKR and behavioral responses. Standard age-appropriate optometric tests also were performed.

Results: Motion coherence thresholds were measured successfully in 336 (91.8%) children using the OKR technique, but only 31 (8.5%) using behavioral responses. The mean threshold was 41.7 ± 13.5% for 2-year-old children and 3.3 ± 1.2% for adults. Within-assessor reliability and test-retest reliability were high in children. Children's motion coherence thresholds were significantly correlated with stereoacuity (LANG I & II test, ρ = 0.29, P < 0.001; Frisby, ρ = 0.17, P = 0.022), but not with binocular visual acuity (ρ = 0.11, P = 0.07). In adults OKR and behavioral motion coherence thresholds were highly correlated (intraclass correlation = 0.81, P = 0.001).

Conclusions: Global motion perception can be measured in 2-year-old children using the OKR. This technique is reliable and data from adults suggest that motion coherence thresholds based on the OKR are related to motion perception. Global motion perception was related to stereoacuity in children.

Keywords: dorsal stream; motion coherence threshold; optokinetic nystagmus; random-dot-kinematogram; vision.

Figure 1

The RDK stimulus. (A) A schematic of the RDK stimulus depicting 50% coherence. Open circles represent signal dots and filled circles represent noise dots. The arrows illustrate the motion direction of each dot. Half of the dots are signal dots (all moving to the right) and the other half are noise dots (moving in random directions). (B) A single frame of the RDK stimulus used in the study.

Figure 2

Percentage of successful measurements for each of the clinical vision tests and global motion measurements for 2-year-old children.

Figure 3

Bland-Altman plot of test–retest reliability for 2-year-old children who completed motion coherence threshold measurements on two separate days. T1, threshold from the first test; T2, threshold from the second test.

Figure 4

The distribution of OKR motion coherence thresholds for 336 2-year-old children.

Figure 5

Examples of psychometric functions for 2-year-old children with associated 95% CIs for proportions. The vertical axis expresses the proportion of trials for which OKR was observed to be in the same direction as the stimulus. (A–C) Three examples of children whose thresholds fell above the 75th percentile (high thresholds). (D–F) Three examples of children whose thresholds were between the 40th and 60th percentile (moderate thresholds). (G–H) Three examples of children whose thresholds fell below the 25th percentile (low thresholds).

Figure 6

A summary of mean motion coherence thresholds from previous studies of global motion perception in infants and children which used RDKs with dynamic signal and noise dots. (A) Results from studies of children aged 1 to 5 months. (B) Results from studies of children aged 3 to 7 years. (C) Results from studies of that also included adult participants. The color of the markers denotes the technique used to measure the motion coherence threshold; blue = OKR, red = preferential looking (PL), and green = behavioral responses. The shape of the markers in combination with the color of the marker denotes the study; = Wattam-Bell, = Bantan and Bertenthal, = Mason et al., = Ellemberg et al., = Gunn et al., = Parrish et al., = Hadad et al., and = Narasimhan and Giaschi. The (a–f) labels are to be used in conjunction with Table A1 provided in the Appendix and identify different stimulus parameters used within individual studies. The black horizontal lines represent the average thresholds found in our study for 2-year-old children (OKR) and adults (OKR and behavioral).