Saccade latencies during a preferential looking task and objective scoring of grating acuity in children with and without visual impairments

Abstract

Purpose: We determined the latencies of orienting responses during a preferential looking task in children with normal vision and in children with visual impairments between 6 and 12 years old, and assessed the feasibility of scoring grating detection in these populations with video-based eye tracking.

Methods: Children performed a computerized preferential looking test, while a remote eye tracker measured the children's eye movements. The stimuli consisted of a 2 × 2 grid, with three uniform grey fields and one target field consisting of a black-and-white square wave grating. The grating was presented randomly at one of the four locations. The spatial frequencies (1.05, 2.11 and 7.02 cyc/deg) were randomly interleaved, with 10 trials per spatial frequency. Three different methods were used to score the accuracy of the responses: (1) primary saccade ends on target, (1) gaze 50% of the presentation time on target, and (3) a combination of method 1 and 2 (i.e. primary saccade ends on target, and/or gaze 50% of the presentation time on target).

Results: The combined scoring method was most reliable to determine whether children could resolve the gratings. Children with visual impairments had significantly lower accuracies than children with normal vision with all three scoring methods. In addition, saccade latencies decreased with age and were significantly longer (62 ± 15 ms) in children with visual impairments.

Conclusion: The use of eye tracking to assess grating detection with a preferential looking task in clinical populations provides valuable additional information, including objective detection measures and developmental delays in saccade latencies.

Keywords: case-control study; child development; orienting response; reaction times; visual acuity.

Figure 1

Stimuli of the preferential looking task. Each trial started with a central fixation dot which was presented for a random duration between 320 and 640 ms. As soon as the fixation spot disappeared, the stimulus array appeared for a duration of 3000 ms. The children were instructed to fixate the fixation dot at the start of each trial and to look at the square wave grating target as soon as the fixation dot disappeared. The target (three different spatial frequencies) appeared randomly at one of the four positions, the other fields were grey.

Figure 2

Illustration of observed response patterns and scoring criteria. (A) Four trials of a child with normal vision (B) four trials of a child with visual impairment due to albinism and with a nystagmus. The target window is indicated with the blue dashed lines, the central fixation window is indicated with the yellow dashed lines, the gaze coordinates are plotted as red lines and the primary saccade is plotted in green.

Figure 3

Flow chart showing the total number participants, the number of children in which we could collect eye tracking data, and the number of children in which the quality of the eye tracking data was deemed sufficient for analysis for (A) children with normal vision, and (B) children with visual impairments. In case eye tracking was not possible, the main reason why the eye tracking failed is listed.

Figure 4

Boxplots of the accuracy of the responses determined with three different scoring methods: 1. Primary saccade ends on the target area (PrimSac), 2. Relative fixation time (RTF) >50%, that is, if the gaze of the participant was on target during 50% of its presentation time, and 3. Primary saccade ends on the grating) or RTF exceeds 50% (Combined). (A) grating‐detection accuracy of the children with normal vision, and (B) grating‐detection accuracy of the children with visual impairments. The colours indicate the spatial frequency of the grating.

Figure 5

Median saccade latencies for the children with normal vision as a function of age and spatial frequency for: (A) all primary saccades. (B) the goal‐directed primary saccades, and (C) the incorrect primary saccades. The lines are the results of the repeated measures anova for the three different gratings.

Figure 6

Median saccade latencies for the children with visual impairments (numbers correspond with individual participants, a circle indicates a child with CVI, Table S1) for (A) gratings of 0.63 LogMAR, (B) gratings of 1.15 LogMAR and (C) 1.45 LogMAR. The solid lines are the result of the repeated measures anova for the children with normal vision, the dashed black lines indicate the 95th percentile in children with normal vision. Latency data were pooled across correct and incorrect trials.