The Development of the Human Visual System In Utero: An Experimental Approach

The overarching aim of this research is to investigate fetal visual perception. Recently it has been determined that the human fetus lives in an environment that is not dark. This project seeks to understand how human fetuses respond to aspects of visual and auditory stimuli presented in utero. The current research will use 2D ultrasound to visualize the fetal lens and record eye movements in response to light and auditory stimuli presented in utero. Aims Aim 1: Do fetuses preferentially orientate to light stimuli in their peripheral visual field? Aim 2: To examine whether fetuses can perform anticipatory gaze. Specifically, can fetuses use an auditory cue to anticipate the appearance of a light stimulus? Aim 3: To examine fetal sensitivity to spatio-temporal cues that correlate with adult interpretations of agentive motion. Aim 4: To examine fetal eye movements in response to a moving visual stimulus. Participants Participants will be healthy volunteers with singleton pregnancies between 33 -36 weeks gestation. Materials Image Acquisition Ultrasound scans will be performed at Waikato Hospital using a Philips Epiq7 Elite Ultrasound System using a 5C1, or 9C2 transducer, keeping TIb<0.3. Individual scans will be recorded in entirety and saved to an external hard drive for offline analysis. Experienced and qualified sonographers will undertake the scanning. Images will be captured in the transverse and parasagittal plane of the fetal face. Stimuli Light Stimulus The light source will consist of one red 4mm LED emitting at 650nm (for part one, two and three) and will consist of two red 2mm LEDs emitting at 650 nm (part four). The light source will be calibrated to specific optical powers dependant on the maternal tissue thickness. This will ensure that consistent levels of light are delivered to the fetus irrespective of variation in maternal tissue thickness. It is estimated that when accounting for dispersion, the light stimuli will broaden to a diameter of 22mm (Del Giudice, 2011). The light stimulus will be presented within the predicted range of the fetal visual system. Presenting this light stimulus to the fetus is completely safe. The level of luminance is lower than what a fetus could be exposed to on a sunny day and poses no risk of damage to the fetal visual system (Del Giudice, 2011). Auditory Stimulus The auditory cue stimulus will be a 500 Hz tone. The intensity of the tone recorded at the maternal abdomen will be 70 dB. The auditory stimulus will be delivered to the fetus by a speaker positioned within 1 meter of the maternal abdomen. Auditory stimulus will be produced using MATLAB. (2018). Tone intensity and frequency are safe and within the range of the fetal auditory system (Graven, 2000) proposed tone frequency and intensity is consistent with experimental studies examining auditory processing in utero (Dunn et al., 2015) Method Study participation consists of attending one 2D ultrasound scan. Time: 60 minutes (approximately). The total time of the sonography scan is approximately 25-30 minutes. The session time of 60 minutes allows the participants to locate the study room, ask questions and familiarise themselves with the researchers and study equipment and debriefing. Study Location: Women’s Health Clinic. Level 1 Elizabeth Rothwell Building, Waikato Hospital. Mothers will lie in a comfortable position as in any normal 2D ultrasound scan. If the fetus is not in a position that will allow an adequate image of the face region or delivery of the visual stimuli, the mother will be asked to take a short walk and/or take a drink of water in order to stimulate movement within the fetus. The following measurements will be taken at the beginning of the scan: fetal biometric measurements including fetal heart rate (FHR), biometric measurements including bi-parietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL) and single deepest pocket (SDP) of amniotic fluid. The measurements will be considered normal for the purposes of this study if: - FHR = 120-180bpm - AC >= 10th percentile - EFW >= 10th percentile - SDP >= 2cm - The fetal eyes are morphologically normal Once these measurements are completed the researchers will move on to presenting the stimuli to the fetus for the separate experiments. • Part One: Anticipatory Gaze 1.) Familiarisation Trails: Present auditory and light stimuli pairing (6x) 12 seconds per trial, 72 seconds total. 2.) Test trails: sound and light present (3x) and sound and no light stimuli (x3) 12 seconds per trial, 72 seconds total. Total time = 144 second (2.4 minutes) • Part 2: Peripheral vs Nasal Responding 1.) Present light stimuli (dot) to the fetal peripheral visual field for 60 secs 2.) Rest period (no stimulus present) for 180 second (3 minutes) 3.) Present light stimuli (dot) to the fetal nasal visual field for 60 secs 4.) Order Counterbalanced Total Time = 300 seconds (5 minutes) • Part 3: Detecting and inducing eye movements 1.) Present light stimuli (dot) to the fetal peripheral visual field for 60 seconds 2.) Light absent (no light stimulus present) for 60 seconds (1 minute) 3.) Order Counterbalanced Total time =120 seconds (2 minutes) • Part 4: Motion Cues 1.) Present agentive motion light stimuli to the fetus 120 seconds (2 minutes) 2.) Present independent motion light stimuli to the fetus 120 seconds (2 minutes) 3.) Order counterbalanced Total time = 300 seconds (5 minutes) Following birth, patient and baby notes will be accessed to gain health information regarding mother and baby. This information will be entered into analysis to account for any potential causes of movement in the fetus during the study. References del Giudice, M. (2011). Alone in the dark? Modeling the conditions for visual experience in human fetuses. Developmental Psychobiology, 53(2), 214–219. https://doi.org/10.1002/dev.20506 Dunn, K., Reissland, N., & Reid, V. M. (2015). The functional foetal brain: A systematic preview of methodological factors in reporting foetal visual and auditory capacity. Developmental Cognitive Neuroscience, 13, 43–52. https://doi.org/10.1016/j.dcn.2015.04.002 Graven, S. N. (2000). Sound and the Developing Infant in the NICU: Conclusions and Recommendations for Care. Journal of Perinatology, 20(S1). https://doi.org/10.1038/sj.jp.7200444