At First Sight: Fetal Eye Movements Reveal a Preference for Face-Like Configurations From 26 Weeks of Gestation

Abstract

Previous research indicates that both adults and newborns show enhanced electrophysiological and behavioral responses to schematic face-like configurations (FCs-three dots composing a downward-pointing triangle), as compared to the inverted configurations (ICs). Even fetuses, when exposed to light stimuli projected through the uterine wall, preferentially orient their heads toward FCs rather than ICs. However, when this effect emerges along the third trimester of pregnancy and in relation to the maturation of which brain structures is still unknown. Here, to provide a sensitive measure of fetal preference for FCs along the whole third trimester, fetal lens movements in response to FCs and ICs was monitored with 2D-ultrasound. In a series of three experiments, fetuses were recruited at 26, 31, and 37 weeks of gestational age and were presented with both flashing and continuous light stimuli. Our results showed that significantly more lens movements were observed in response to continuous as compared to flashing light stimuli. Furthermore, lens movements linearly increased within the third trimester and, regardless of the time-point, significantly more lens movements were observed in response to FCs versus ICs. We also found a significant correlation in the first time-point, wherein the greater the FCs versus ICs differential response the larger the thalamic nuclei dimension. These findings suggest that FC preference is already present at the beginning of the third trimester, as soon as thalamocortical projections are established.

Keywords: 2D ultrasound; face‐like configuration preference; fetal eye‐movements; fetuses.

FIGURE 1

Conceptual illustration of the experimental setting and procedures for Experiments 1–2. (A: Top) Graphical representation of the experimental setting with the pregnant women concurrently subjected to the sonographic exam and to the fetal visual stimulation. An experimenter, blinded to the purpose of the study, manually displaced the visual stimulator in a horizontal direction across the maternal abdomen (5 left‐to‐right and 5 right‐to‐left experimental trials). Bottom: experimental visual stimuli delivered to the fetus through the maternal abdomen, depicting either a downward pointing (i.e., FCs) or an upward pointing triangle (i.e., ICs). (B) Experimental procedures for Experiment 1a (N = 17; g.a.: 37 weeks), employing continuous visual stimuli. (C) Experimental procedures for Experiment 1b (N = 8; g.a.: 37 weeks), with two stimulation modalities (continuous and flashing light). (D) Experimental procedure for Experiment 2, where responses of the fetuses in three time‐points of the third trimester were compared (N = 9; g.a.: 26; N = 8; g.a.: 31; and N = 9; g.a.: 37 weeks).

FIGURE 2

Results Experiment 1a. Main effect of stimulus orientation: percentage of lens movements in response to FCs and ICs (see Supporting Information for further detail on statistical analyses). Notice the significantly greater number of movements in response to FCs. Error bars represent standard error of the mean (SEM). ***p < 0.005.

FIGURE 3

Results Experiment 1b. (A [left panel]) Main effect of stimulus orientation: percentage of lens movements in response to FC and IC stimuli. Notice that movements in response to FCs are significantly greater than those in response to ICs. (B [central panel]) Main effect of stimulation condition: percentage of lens movements with continuous versus flashing light. A significantly greater number of movements is observed in response to continuous as opposed to flashing light (C [right panel]). Interaction: percentage of lens movements for FCs and ICs stimuli, with continuous versus flashing light stimulations. As depicted in the graph, no significant interaction between the two factors was found. Error bars represent the standard error of the mean (SEM). *p < 0.05; **p < 0.01.

FIGURE 4

Results Experiment 2. (A) Main effect of gestational age: percentage of lens movements observed at each time‐point. (B) Main effect of stimulus orientation: percentage of lens movements for FCs and ICs. Notice the presence of a significant difference between the two conditions. (C) Nonsignificant interaction: Percentage of lens movements for FCs and ICs stimuli at each time‐point. Results show significant difference between FCs and ICs at all time‐points. Error bars represent the standard error of the mean (SEM). **p < 0.01. (D) Total lens movements by fetal age correlation: Significant positive correlation between the percentage of total lens movements and fetuses’ g.a. in days.

FIGURE 5

Relation of face‐like preference effect with the thalamic dimension. (A) Adjusted means of the Face‐like preference Index in each time point. (B) Face‐like preference Index by Thalamic nuclei correlation: Significant positive correlation between the Face‐like preference Index (delta between movements in response to face‐like and inverted configurations) and thalamic nuclei growth (mm) in 26‐week‐old fetuses.